The manual of photography

The Manual of Photography


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The Manual of
Photography
Tenth Edition

Edited by
Elizabeth Allen
Sophie Triantaphillidou

AMSTERDAM  BOSTON  HEIDELBERG  LONDON  NEW YORK  OXFORD
PARIS  SAN DIEGO  SAN FRANCISCO  SINGAPORE  SYDNEY  TOKYO
Focal Press is an imprint of Elsevier


Focal Press is an imprint of Elsevier
The Boulevard, Langford Lane, Kidlington, Oxford, OX5 1GB, UK
30 Corporate Drive, Suite 400, Burlington, MA 01803, USA
The Ilford Manual of Photography
First published 1890
Fifth edition 1958
Reprinted eight times
The Manual of Photography
Sixth edition 1970
Reprinted 1971, 1972, 1973, 1975
Seventh edition 1978

Reprinted 1978, 1981, 1983, 1987
Eighth edition 1988
Reprinted 1990, 1991, 1993, 1995 (twice), 1997, 1998
Ninth edition, 2000
Tenth edition, 2011
Copyright Ó 2011 Elizabeth Allen & Sophie Triantaphillidou. Published by Elsevier Ltd. All rights reserved.
The rights of Elizabeth Allen & Sophie Triantaphillidou to be identified as the authors of this work has been asserted in accordance with the
Copyright, Designs and Patents Act 1988
No part of this publication may be reproduced or transmitted in any form or by any means, electronic or mechanical, including
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herein).
Notices
Knowledge and best practice in this field are constantly changing. As new research and experience broaden our understanding, changes
in research methods, professional practices, or medical treatment may become necessary.
Practitioners and researchers must always rely on their own experience and knowledge in evaluating and using any information, methods,
compounds, or experiments described herein. In using such information or methods they should be mindful of their own safety and
the safety of others, including parties for whom they have a professional responsibility.
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Library of Congress Control Number: 2010933573
ISBN: 978-0-240-52037-7
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10 11 12 11 10 9 8 7 6 5 4 3 2 1


Contents
Preface .................................................................... xv
Editors’ Acknowledgements ............................... xvii
Author Biographies ............................................ xviii
1. Introduction to the imaging process ........... 1
Introduction ............................................................ 1
The imaging process............................................... 2
Image control.......................................................... 3
Control of image shape ..................................... 3
Depth of field...................................................... 5
Tone and contrast............................................... 5
Colour.................................................................. 6
The origins of photography .................................. 6
Camera obscura .................................................. 6
Early experiments ............................................... 6
Towards the development process e the
Daguerreotype..................................................... 7
The negativeepositive process .......................... 7
Modern materials ............................................... 7
Photographic imaging today................................. 8
Characteristics of photographic materials ....... 8
Capturing colour ................................................ 9
Digital imaging ..................................................... 10
Early digital images .......................................... 10
The CMOS sensor............................................. 11
Colour digital capture...................................... 11
Other digital devices ........................................ 12

Digital image representation............................... 12
Spatial resolution ............................................. 14
Bit depth............................................................ 14
Colour representation ...................................... 15
File size and file formats ................................. 15
Imaging chains...................................................... 15
Evaluating image quality ..................................... 17
Bibliography.......................................................... 18

2. Light theory .................................................. 19
Introduction .......................................................... 19

A brief history of light theory ............................. 19
Waveeparticle duality.......................................... 20
The nature of light................................................ 20
Radiometry and photometry............................... 21
Radiometric definitions ................................... 21
Photometric definitions................................... 21
Optics..................................................................... 21
Wave theory .......................................................... 22
Simple harmonic motion ................................ 23
Principle of superposition ............................... 25
Plane waves ....................................................... 27
Light intensity ................................................... 27
Refraction and dispersion................................ 27
Polarization....................................................... 28
Interference........................................................ 30
Diffraction ......................................................... 32
Diffraction of a circular aperture
and a single slit................................................. 32

Rayleigh criterion.............................................. 34
The electromagnetic spectrum ............................ 35
Black-body radiation............................................ 37
Wien’s Displacement Law ............................... 38
Planck’s Law...................................................... 38
The photoelectric effect........................................ 39
The photon............................................................ 40
Bohr model of the atom...................................... 40
The emission of electromagnetic
radiation in atoms................................................ 41
Bibliography.......................................................... 42

3. Photographic light sources ......................... 43
Introduction .......................................................... 43
Characteristics of light sources............................ 43
Spectral quality ................................................. 43
Spectral power distribution curve .................. 43
Colour temperature.......................................... 44
Colour rendering .............................................. 45
Percentage content of primary hues............... 45
Measurement and control of colour
temperature ....................................................... 45
v


Contents
The mired scale................................................. 46
Light output .......................................................... 46
Units................................................................... 46
Illumination laws ............................................. 46

Reflectors and luminaires ................................ 47
Constancy of output ........................................ 48
Efficiency ........................................................... 48
Daylight ................................................................. 48
Tungsten filament lamps ..................................... 49
Tungstenehalogen lamps.................................... 49
Fluorescent lamps................................................. 50
Metal-halide lamps............................................... 50
Pulsed xenon lamps ............................................. 50
Expendable flashbulbs ......................................... 50
Electronic flash...................................................... 52
Flash circuitry.................................................... 52
Flash output and power .................................. 52
Flash duration and exposure........................... 53
Portable units.................................................... 53
Studio flash ....................................................... 53
Automatic flash exposure ................................ 54
Integral flash units............................................ 54
Red-eye avoidance ............................................ 55
Other sources ........................................................ 55
Light-emitting diodes....................................... 55
Diode lasers....................................................... 57
Bibliography.......................................................... 57

4. The human visual system ........................... 59
Introduction .......................................................... 59
The physical structure of the human eye........... 59
Tunics................................................................. 60
Cornea ............................................................... 60
Conjunctiva ....................................................... 60

Iris and pupil .................................................... 60
Crystalline lens ................................................. 61
Ciliary body ...................................................... 61
Vitreous cavity and vitreous humour............. 61
Retina and choroid........................................... 61
Optic nerve........................................................ 62
Structure of the retina ...................................... 62
Rods and cones................................................. 64
‘Non-imaging’ cell layers ................................. 66
Receptive fields ................................................. 67
Dark adaptation.................................................... 68
Elementary colour vision..................................... 69
YoungeHelmholtz theory of colour
vision ................................................................. 69
Opponent theory of colour vision ................. 69
Colour anomalous vision.................................... 69
Movement and Focusing ..................................... 70
Focusing and correction of eyesight............... 70
Movement ......................................................... 71
The visual pathway............................................... 72
Visual cortex...................................................... 72
vi

Binocular vision.................................................... 72
Performance of the eye ........................................ 73
Luminance discrimination .............................. 73
Contrast sensitivity function ........................... 74
Visual acuity ...................................................... 74
Animal vision........................................................ 74
Bibliography.......................................................... 76

5. Introduction to colour science ................... 77
Introduction .......................................................... 77
The physics of colour........................................... 77
Colour terminology ............................................. 77
The colour of objects ........................................... 78
Spectral absorptance, reflectance and
transmittance .................................................... 79
CIE standard illuminating and viewing
geometries ............................................................. 80
CIE standard illuminants and sources ............... 81
Models of colour vision....................................... 82
The basics of colorimetry .................................... 84
Colour matching functions and the CIE
standard observers............................................ 86
Calculating tristimulus values from
spectral data ...................................................... 87
Chromaticity diagrams .................................... 88
CIE uniform colour spaces and colour
differences ......................................................... 91
Metamerism and types of metameric
matches.............................................................. 92
The appearance of colours .................................. 94
Visual adaptation and related
mechanisms ...................................................... 94
Other colour appearance phenomena ........... 96
An introduction to CATs and CAMs .................. 97
A generalized CAT ............................................ 97
Colour appearance models (CAMs)............... 98
Colour reproduction ............................................ 98

Objectives of colour reproduction ................. 99
Instruments used in colour measurement.......100
Viewing conditions.............................................101
Bibliography........................................................102

6. Photographic and geometrical optics...... 103
Introduction ........................................................103
Photographic optics ...........................................103
Optical materials ............................................103
Reflection.........................................................104
Refraction ........................................................104
Transmission ...................................................104
Dispersion .......................................................105
Polarization.....................................................105
Geometrical optics .............................................106
Simple lens......................................................106
Cardinal planes...............................................106
Focal length.....................................................107


Contents
Image magnification ......................................108
Mirrors .............................................................109
Optical calculations............................................109
Parameters .......................................................109
Equations.........................................................109
Focusing movements .....................................110
Depth of field and depth of focus................111
The photometry of image formation ...............111
Stops and pupils.............................................111

Aperture ...........................................................112
Image luminance and illumination .............112
Image illuminance..........................................113
Exposure compensation for close-up
photography....................................................114
Lens flare .........................................................114
T-numbers .......................................................115
Anti-reflection coatings ..................................115
Types of coating..............................................116
Bibliography........................................................117

7. Images and image formation ................... 119
Introduction ........................................................119
Sinusoidal waves ................................................120
Modulation .....................................................121
Images and sine waves...................................121
Imaging sinusoidal patterns..........................123
Fourier theory of image formation ..................124
Linear, spatially invariant systems................124
Spread functions.............................................125
The point spread function (PSF) ..................126
The line spread function (LSF) .....................126
The edge spread function (ESF)....................126
The imaging equation (from input
to output)........................................................127
The imaging equation in one dimension....128
The modulation transfer function (MTF)....128
Special Fourier transform pairs.........................130
The rectangular function................................130
The Dirac delta function................................130

Properties of d(x)............................................131
Importance of d(x) .........................................132
The Gaussian function ...................................132
The modulation transfer function
revisited ...............................................................132
Cascading of MTFs .........................................133
Convolution revisited ........................................133
A geometric interpretation of
convolution.....................................................133
The convolution theorem..............................133
Discrete transforms and sampling....................134
Undersampling a cosine wave ......................134
The Dirac comb (the sampling function) ...134
The process of sampling ................................135
The MTF for a CCD imaging array...............137
Bibliography........................................................138

8. Sensitometry ............................................... 139
Introduction ........................................................139
The subject ..........................................................139
Exposure ..............................................................139
Density and other relevant measures...............140
Transmittance..................................................140
Opacity ............................................................140
Density.............................................................140
Effect of light scatter in a negative ...................140
Callier coefficient............................................141
Density in practice..............................................142
The Characteristic (H and D) curve .................143
Main regions of the negative characteristic

curve.................................................................143
Variation of the characteristic curve with
the material .....................................................144
Gammaetime curve.......................................145
Variation of gamma with wavelength..........145
Placing the subject on the characteristic
curve.....................................................................146
Effect of variation of exposure of the
negative............................................................146
Average gradient and G......................................146
Contrast index.....................................................147
Effect of variation in development on the
negative................................................................147
Exposure latitude................................................147
The response curve of a photographic
paper ....................................................................148
Maximum black..............................................148
Exposure range of a paper.............................149
Variation of the print characteristic
curve with the type of emulsion...................149
Variation of the print characteristic
curve with development ................................149
Requirements in a print.....................................150
Paper contrast .................................................150
Reciprocity law failure .......................................151
Practical effects of reciprocity failure ...........151
Intermittency effect.........................................152
Sensitometers ......................................................152
Densitometers .....................................................152
Microdensitometers........................................153

Colour densitometers ....................................153
Bibliography........................................................154

9. Image sensors ............................................. 155
Introduction ........................................................155
Materials and detection of light .......................155
Conductors, insulators and
semiconductors...............................................156
Doping.............................................................157
Photoemission and photoabsorption..........158
Diodes..............................................................159
Transistors .......................................................159
vii


Contents
CCD and CMOS sensors ...............................159
MOS capacitor ................................................159
Photodiodes ....................................................160
Pixels ................................................................160
CCD and CMOS image readout.......................160
CCD readout ...................................................161
CMOS readout ................................................164
Amplification and analogue-to-digital
conversion ...........................................................164
Scanning methods..............................................166
Imaging performance.........................................167
Performance trade-offs...................................167
Microlens arrays..............................................169
Sensitivity ........................................................169

Exposure control.............................................170
Sensor imperfections......................................171
Generating colour...........................................171
Bibliography........................................................173

10. Camera lenses ............................................ 175
Lens aberrations .................................................175
Introduction....................................................175
Axial chromatic aberration............................175
Lateral chromatic aberration.........................176
Spherical aberration .......................................177
Coma ...............................................................178
Curvature of field ...........................................178
Astigmatism ....................................................178
Curvilinear distortion ....................................178
Lens aperture and performance....................180
Photographic lenses ...........................................180
Photographic lens types ....................................181
Simple lenses ..................................................181
Compound lenses ..........................................181
Development of the photographic
lens...................................................................182
Simple lenses and achromats .......................182
The Petzval lens..............................................182
Symmetrical doublets ....................................182
Anastigmats.....................................................183
Triplets.............................................................184
Double-Gauss lenses......................................184
Modern camera lenses .......................................184
Wide-angle lenses...............................................185

Symmetrical-derivative lenses.......................185
Retrofocus lenses ............................................186
Fish-eye lenses ................................................186
Long-focus lenses ...............................................186
Long-focus designs .........................................186
Telephoto lenses.............................................186
Catadioptric lenses (‘mirror lenses’) ............187
Zoom and varifocal lenses ................................188
Zoom lenses....................................................188
Zoom lenses for compact and digital
cameras............................................................190
viii

Macro lenses .......................................................191
Optical attachments...........................................191
Afocal converter lenses ..................................191
Close-up (supplementary) lenses.................192
Other attachments..........................................192
Teleconverters .................................................193
Optical filters ......................................................194
Absorption filters............................................194
UV and IR filters.............................................195
Neutral-density filters ....................................196
Polarizing filters .............................................196
Bibliography .......................................................197

11. Photographic camera systems .................. 199
Introduction........................................................199
Image format ......................................................199
Camera types ......................................................199

Simple cameras...............................................199
Compact cameras ...........................................200
Rangefinder cameras ......................................202
Twin-lens reflex (TLR) cameras ....................202
Single-lens reflex (SLR) cameras...................202
Technical cameras ..........................................203
Special-purpose cameras ...................................204
Cameras for self-developing materials ........204
Aerial cameras.................................................204
Underwater cameras ......................................204
Ultrawide-angle cameras ...............................204
Panoramic cameras ........................................205
Automatic cameras.............................................206
Analogue systems ...........................................206
Digital control ................................................206
Camera features..................................................207
Shutter systems...............................................207
Flash synchronization....................................209
The iris diaphragm .........................................211
Viewfinder systems.........................................213
Focusing systems ............................................214
Autofocus systems..........................................217
Exposure metering systems ...............................219
Automatic exposure .......................................219
Programmed exposure modes ......................219
Segmented photocell systems.......................221
Battery power......................................................222
Camera shake and image stabilization............223
Camera movements ...........................................224
Bibliography .......................................................225

12. Exposure and image control .................... 227
Camera exposure................................................227
Exposure relationships and logarithms ...........228
Relative aperture.............................................229
Shutter speed ..................................................229
Subject luminance ratio.....................................229
Dynamic range of sensors .................................230


Contents
Optimum exposure and the transfer
function ...............................................................231
Exposure meters .................................................232
Hand-held exposure meters ..........................232
Acceptance angle ............................................234
Exposure values ..............................................235
Exposure factors .............................................235
Reciprocity law failure .......................................236
Types of light measurement..............................237
Incident light measurement ..........................237
Reflected light measurement.........................237
In-camera metering modes ...............................237
Spot metering .................................................237
Partial area metering......................................237
Centre-weighted average metering ...............237
Matrix or multi-zone metering .....................238
Electronic flash exposure...................................238
Guide numbers...............................................238
Reflected light measurement techniques .........239

Measurement of total scene
luminance .......................................................239
Measuring a middle grey surface
(key tone)........................................................239
Measurement of luminance of the
darkest shadow...............................................240
Measurement of luminance of the
lightest highlight ............................................240
Averaging values.............................................240
Exposure techniques and digital
cameras................................................................240
Using the image histogram ...........................240
‘Exposing to the right’....................................241
The zone system .................................................241
The zones ........................................................241
The zone system and digital cameras ..........242
High-dynamic-range (HDR) imaging ..............242
Bibliography .......................................................243

13. Image formation and the photographic
process ........................................................ 245
Introduction........................................................245
Silver halides.......................................................245
Latent image formation.....................................247
Spectral sensitivity of photographic
materials ..............................................................248
Response of photographic materials
to short-wave radiation .................................248
Response of photographic materials
to visible radiation.........................................249

Spectral sensitization .........................................249
Orthochromatic materials .............................249
Panchromatic materials .................................249
Extended sensitivity materials.......................250
Infrared materials ...........................................250

Other uses of dye sensitization ....................250
Structure of photographic materials ................251
Production of light-sensitive materials
and sensors .....................................................251
The support.....................................................252
Coating the photographic emulsion............252
Sizes and formats of photographic
materials ..............................................................253
Speed of photographic materials .....................253
Speed systems and standards........................254
Characteristics of photographic
materials ..............................................................255
Graininess and granularity............................255
Contrast ...........................................................255
Sharpness and acutance.................................256
Chemistry of the photographic process...........256
Developers and development .......................256
Composition of a developing solution .......256
Developing agents..........................................257
Preservatives....................................................257
Alkalis ..............................................................258
Restrainers (anti-foggants) ............................258
Miscellaneous additions to developers........258
Superadditivity (Synergesis)..............................259

Development time .........................................259
Printing................................................................259
Darkroom work..............................................260
Development ..................................................260
Bibliography .......................................................260

14. Digital cameras and scanners ................... 263
Digital still cameras ...........................................263
Digital still camera architecture........................263
Imaging optics ....................................................265
Image sensor .......................................................267
Shutter systems ...................................................268
Dynamic range in digital cameras....................269
Colour capture....................................................269
Three-sensor cameras .....................................270
Sequential colour cameras ............................270
Colour filter array (CFA) cameras ................270
The Super CCDÔ ...........................................271
The FoveonÔ sensor......................................272
Rendered versus unrendered camera
processing............................................................272
Exposure determination and
auto-exposure .....................................................273
Autofocus control...............................................273
Analogue processing ..........................................274
Digital processing...............................................274
Colour demosaicing.......................................274
Setting white balance.....................................275
Digital zoom, resizing and cropping ...........276
Noise reduction ..............................................276

Sharpening ......................................................277
ix


Contents
Tone/colour rendering.......................................277
Camera types ......................................................277
Compact digital cameras...............................278
Bridge digital cameras....................................279
Digital single-lens reflex (DSLR)
cameras............................................................279
Digital cameras and camera backs
for medium and large format.......................280
Specialist digital cameras...............................280
Image scanners ...................................................280
Types of scanners ...............................................282
Drum scanners................................................282
Flatbed scanners .............................................282
Film scanners ..................................................283
Flextight scanners ...........................................284
Multi-spectral scanners ..................................284
Scanner characteristics .......................................284
Sampling and resolution...............................284
Dynamic range ...............................................285
Bit depth..........................................................286
Scanning speed ...............................................286
Image transfer .................................................286
Scanner drivers ...............................................286
Bibliography .......................................................287

15. Displays ...................................................... 289
Introduction........................................................289
Image display......................................................289
Cathode ray tube (CRT) displays .....................289
Liquid crystal displays (LCDs) .........................293
Other display technologies ...............................296
Plasma display panels (PDPs)......................296
Organic light-emitting displays (OLEDs)....296
Flexible displays .............................................297
Characteristics of displays .................................297
Refresh rate and response time ....................297
Resolution .......................................................298
Luminance ......................................................299
Contrast ratio..................................................299
Viewing angle .................................................299
Colour .............................................................300
Display artefacts .............................................301
Effect of viewing conditions .............................302
Bibliography .......................................................302

16. Digital printing and materials.................. 303
Introduction........................................................303
Printing technologies .........................................303
Inkjet printers .................................................303
Electrophotographic printers ........................305
Thermography ................................................307
Pictrography....................................................308
Printing media and their properties ................308
Paper for inkjet printing................................309
Inks for inkjet printing ..................................309

x

Toner materials...............................................310
Colour, resolution and output .........................310
Half-toning and dithering .............................310
Resolution .......................................................311
Printing press ......................................................312
Relief printing .................................................313
Planographic printing (or lithography).......313
Recess printing................................................313
Through printing............................................313
Bibliography .......................................................314

17. Digital image file formats ......................... 315
Introduction........................................................315
Raster and vector graphics.............................315
Bit-depth support and colour encoding ......316
Compression methods ..................................316
Standardization of the format ......................316
Metadata and Exif ..........................................317
Colour management......................................317
Additional features.........................................317
Tagged image file format (TIFF).......................317
TIFF/EP ............................................................318
TIFF/IT .............................................................319
Joint Photographic Experts Group (JPEG)......319
Joint Photographic Experts Group 2000
(JPEG 2000)........................................................320
RAW .....................................................................321
Digital negative (DNG) .....................................322

Graphics interchange format (GIF)..................323
Portable network graphics (PNG)....................324
Photoshop document (PSD) ............................325
Photo CD (PCD)................................................326
Postscript (PS) and encapsulated
postscript (EPS) ..................................................326
EPS ...................................................................327
Portable document format (PDF)....................327
Bibliography .......................................................327

18. Image storage and archiving .................... 329
Introduction........................................................329
Life expectancy of traditional
photographic media...........................................329
Processing conditions ....................................331
Dark fading .....................................................331
Light fading.....................................................333
Storage conditions .........................................334
Atmospheric gases..........................................336
Toning .............................................................336
Life expectancy of digital prints........................336
Printing technologies and media .................337
Permanence factors and test for digital
prints................................................................338
Digital image storage and longevity ................339
Magnetic storage.............................................340
Optical disc storage........................................340


Contents

Other digital image archiving issues............342
Bibliography .......................................................343

19. Introduction to image quality and system
performance ............................................... 345
Introduction........................................................345
Subjective and objective image quality ...........345
Image quality assessment..............................346
Basic image quality attributes
(or dimensions) .............................................346
The image quality circle ................................348
Further image quality attributes ...................349
Digital image artefacts .......................................350
Distortion, fidelity and quality.........................351
Image distortion .............................................351
Image fidelity ..................................................351
Image quality ..................................................352
The use of a reference image ........................353
Test charts and test scenes.................................353
Test charts........................................................353
Test scenes.......................................................354
Image psychophysics .........................................354
Psychometric scales........................................355
The psychometric function ...........................355
Scaling methods .............................................356
Scene dependency in image quality.................357
Choice of test scenes......................................360
Image quality metrics and models...................361
Bibliography .......................................................363

20. Speed and sensitivity................................. 365
Sensitivity of imaging systems..........................365
Spectral sensitivity of digital cameras ..........366
Measurement of the spectral sensitivity
of digital cameras ...........................................366
Determination of the colour sensitivity
of an unknown photographic
emulsion .........................................................367
Wedge spectrograms ......................................367
Uses of wedge spectrograms .........................368
Speed of imaging systems .................................368
Methods of expressing speed ........................368
Threshold systems ..........................................369
Fixed density ...................................................369
Inertia ..............................................................369
Minimum useful gradient .............................369
Fractional gradient .........................................370
Speed systems and standards........................370
ISO speed ratings for colour silver-based
materials ..............................................................372
Colour negative film ......................................372
Colour reversal film .......................................372
Speed of digital systems ....................................373
Speed based on saturation (Ssat)..................373

Speed based on noise (Snoise).......................374
Standard output sensitivity (SOS) ...............374
Recommended exposure index (REI) ..........374
Digital camera ISO settings...........................374
Typical sensitivities of film and CCD

devices and speed ratings in practice...............374
Bibliography .......................................................375

21. Tone reproduction..................................... 377
Theory of tone reproduction ............................377
Transfer functions and gamma.....................377
Overall transfer function and overall
gamma.............................................................378
Subjective tone reproduction,
optimum gamma and viewing
conditions .......................................................378
Quadrant diagram..........................................379
Tone reproduction of imaging devices
and image encoding systems ............................380
CRT display transfer function .......................380
Liquid crystal display (LCD) transfer
function ...........................................................382
Measuring display transfer functions...........382
Transfer functions of digital acquisition
devices .............................................................383
Measuring acquisition device transfer
functions .........................................................384
Image encoding: sRGB, Adobe RGB
and JPEG transfer functions..........................384
Transfer functions of printers .......................386
Other measures related to tone and
contrast ................................................................386
Dynamic range and contrast ratio................386
Contrast in uniform areas, test
targets and images..........................................387

Non-linear quantization, bit-depth
requirements and gamma correction...............388
Bibliography .......................................................391

22. Photographic colour reproduction .......... 393
Introduction........................................................393
Complementary pairs of colours..................393
Colour photographic processes ........................393
Additive colour photography .......................394
Subtractive processes......................................395
Integral tripacks ..............................................395
Formation of subtractive image dyes...........396
Colour sensitometry ..........................................396
Negativeepositive colour ..............................396
Reversal colour ...............................................399
Colour photographic materials ........................400
Location of colour formers ...........................401
Colour processing ..............................................401
Reversal process..............................................402

xi


Contents
Negativeepositive process ............................403
Prints from transparencies ............................405
Enhancement of colour reproduction .............407
Colorimetry of photographic images ..............408
Bibliography .......................................................409

23. Digital colour reproduction ..................... 411
Introduction........................................................411
Colour space and colour encoding ..................412
Classification of colour spaces..........................412
RGB (red, green, blue)...................................413
CMY(K) (cyan, magenta, yellow,
black)...............................................................413
HSL (hue, saturation, lightness) e and
similar..............................................................413
YCC (luminance, chrominance 1,
chrominance 2) e and similar .....................413
CIE colour spaces ...........................................413
Colorimetric colour spaces ...........................414
Colour appearance spaces .............................414
Device dependent colour spaces ..................414
Image state ..........................................................414
Sensor colour encoding .................................414
Scene-referred colour encoding ....................414
Output-referred colour encoding .................415
Original-referred colour encoding................415
Standard colour space and colour space
encodings ............................................................416
sRGB (standard RGB) and
sRGB-related colour space encodings ..........416
sYCC and sYCC-related .................................418
ROMM RGB and RIMM RGB .......................419
Adobe RGB 1998 ...........................................419
Device colour characterization .........................419
Physical models..............................................420
Numerical models..........................................422

Regression .......................................................423
Look-up tables with interpolation ...............424
Evaluation of the characterization
model ..............................................................425
Characterization of displays .............................426
Characterization of digital input devices ........428
Gamut mapping .................................................429
Gamut mapping aims....................................430
Gamut mapping techniques .........................430
Bibliography .......................................................432

24. Noise, sharpness, resolution and
information ................................................ 433
Introduction........................................................433
Image noise.........................................................433
Causes of noise in an image .........................433
Photographic noise ............................................434
Graininess .......................................................434

xii

Factors affecting the graininess
of prints...........................................................436
Granularity ......................................................436
Factors affecting negative granularity...........436
Variation of granularity with density...............437
Quantifying image noise...................................437
Variance ...........................................................438
Estimating s2 ..................................................438
Selwyn’s law....................................................438

The autocorrelation function ........................438
The noise power spectrum ............................438
Relationships between noise measures .......439
Practical considerations for the
autocorrelation function and the noise
power spectrum..............................................440
Using the autocorrelation function..............440
Direct Fourier transformation of noise
samples............................................................440
Signal-to-noise ratio.......................................441
Electronic system noise .....................................442
Resolution, sharpness and MTF .......................443
Resolving power of photographic
systems ............................................................443
Measuring modulation transfer
functions .........................................................445
Wave recording e sine-wave method ..........446
Wave recording e square-wave
methods...........................................................446
Edge input method ........................................446
Slanted edge method .....................................447
MTF correction ...............................................449
Resolving power and MTF for optical
systems ............................................................449
Sharpness, MTF and image quality ..............450
Detective quantum efficiency (DQE) ..............451
General considerations ..................................451
DQE for the photographic process ..............453
DQE for a CCD or CMOS imaging
array .................................................................453

DQE and signal-to-noise ratio......................454
Information theory ............................................454
Information capacity of images....................455
Bibliography .......................................................456

25. Digital image workflow ............................ 457
Imaging chains and image workflow...............457
Principles guiding effective workflow..............458
Workflow approach ...........................................459
Resolution and the digital imaging
chain ....................................................................459
Interpolation...................................................460
Interpolation methods and associated
artefacts............................................................461
Interpolation and image workflow ..............462


Contents
Calculating required resolution for
image output ..................................................462
Bit depth: 8-bit versus 16-bit imaging.............463
Colour management..........................................464
Colour workflow ............................................465
File formats .........................................................466
Image acquisition...........................................466
RAW capture and workflow ..........................467
Image editing ..................................................469
Image output ..................................................469
Image archiving ..............................................470
Image optimization workflow ..........................470

Workflow examples............................................471
1. Commercial photography.........................471
2. Forensic imaging........................................472
3. Medical imaging ........................................472
Acknowledgements ............................................473
Bibliography .......................................................473

26. Colour management systems ................... 475
Introduction........................................................475
Colour management tasks ................................475
Closed-loop versus open-loop colour
management .......................................................476
The International Color Consortium
(ICC)....................................................................477
ICC colour management architecture..............478
The profile connection space (PCS).................479
Rendering intents ...............................................479
The ICC perceptual intent reference
medium and reference viewing
conditions .......................................................481
ICC profiles.........................................................481
Using profiles......................................................483
Profile processing models .................................484
Profile structure ..................................................486
Structure of device profiles............................487
Structure of colour space conversion
profiles.............................................................489
Creating custom device profiles .......................490
Display profiles...............................................490
Input profiles ..................................................491

Scanner profiling ............................................492
Digital camera profiling ................................492
Using camera profiles ....................................492
Output profiles ...............................................493
Colour management workflow ........................495
Colour rendering options .............................496
Early-binding versus late-binding
workflow .........................................................496
RGB and CMYK workflows ...........................496
Using an intermediate colour space ............497
Proofing and soft-proofing images ..............498
Bibliography .......................................................499

27. Spatial image processing........................... 501
Introduction........................................................501
Background .........................................................501
Structure of the digital image .......................501
Implementation of spatial domain
processes..........................................................502
Linear systems theory ....................................503
Discrete convolution..........................................503
Point processing operations: intensity
transformations ..................................................503
Brightness and contrast changes using
linear transformation functions ...................503
Piecewise linear functions .............................504
Image thresholding and quantization .........504
Power-law transformations: gamma
correction ........................................................505
Point processing: multiple image

operations ...........................................................507
Enhancement using arithmetic
operations .......................................................507
Enhancement using logic operations...........507
Point processing: statistical operations............507
The image histogram .....................................507
Probability density function and
probability distribution function .................508
Histogram slide and stretch ..........................510
Histogram equalization.................................510
Point processing: geometric
transformations ..................................................512
Neighbourhood processing: spatial
filtering techniques.............................................512
Linear filtering ....................................................512
Properties of linear filters ..............................513
Types of linear filters and their
applications.........................................................514
Smoothing spatial filters ...............................514
Edge detection and sharpening spatial
filters ................................................................515
Non-linear spatial filtering................................518
Median filters..................................................518
Minimum and maximum filters...................520
Bibliography .......................................................520

28. Digital image processing in the
frequency domain ..................................... 521
Introduction........................................................521
Fourier series and transform revisited .............522

Fast Fourier transform (FFT).............................523
Imaging equation revisited ...............................523
Linear spatial filtering (convolution) ..............523
Frequency-domain filtering...............................524
Low-pass filtering ...........................................526
High-pass filtering ..........................................526
xiii


Contents
High-boost filter .............................................527
Band-pass and band-Stop filters.......................527
Image restoration ...............................................529
Inverse filtering ...............................................529
Optimal or Wiener filtering ..........................531
Maximum entropy reconstruction ...............531
Interactive restoration ....................................532
Extended depth of field (EDOF) ..................532
Wavelet transform ..............................................532
Discrete wavelet transform............................533
Bibliography .......................................................534

29. Image compression ................................... 535
Introduction........................................................535
Uncompressed image file sizes.........................535
Image data and information.............................535
Basis of compression .........................................536
Types of redundancy......................................537
Measuring compression rate .........................538
Scene dependency and compression ...........539

Information theory ............................................539
Entropy and image structure.........................540
Shannon’s theorem ........................................541

xiv

Image compression models ..............................542
Lossless compression .........................................543
Lossless compression methods.....................543
Reducing spatial redundancy........................543
Reducing coding redundancy:
variable-length coding ...................................545
Lossy compression .............................................546
Evaluating lossy compression...........................547
Distortion metrics ..........................................547
Alternative assessment methods...................548
Lossy compression methods .............................548
Quantization...................................................549
Lossy compression standards............................549
Joint Photographic Experts Group
(JPEG) standard..............................................549
JPEG 2000 standard.......................................551
Bibliography .......................................................552

Appendix A .......................................................... 553
Appendix B .......................................................... 555
Index ..................................................................... 557


Preface

to the tenth edition

Although there are many textbooks, monographs and manuals that are available today dedicated to
what has now become imaging, The Manual of Photography stands out as a significant and unique
publication. It was first published in the very early days of photography in 1890 under the editorship
of C.H. Bothamley at the request of the then Ilford Company as The Ilford Manual of Photography. The
preface to this first edition has set the scene for all later editions:
. an endeavour has been made to state, in a simple way, sufficient of the principles to enable the reader to
work intelligently, and to overcome most of the difficulties that he is likely to meet with .
This firm foundation has persisted throughout all subsequent editions under the guidance of
a number of editors leading to this tenth edition.
It has been revised and reprinted many times under only five editors during its 120-year period of
publication. Forty years after its initial publication, George E. Brown provided a complete revision
and started the tradition of using a number of specialist authors. This reflected the changes in
photography that no longer could be fully understood and explained by a single author. The second
edition appeared in 1942 under the editorship of James Mitchell, and the third and fourth editions
rapidly followed in 1944 and 1949 respectively.
Alan Horder edited the fifth and sixth editions. The sixth edition of 1971 saw the move away from
publication by Ilford Limited when it was acquired by the present publishers and the name Ilford was
removed from the title. This edition also saw contributions for the first time by two of the contributors
to this edition: Sidney Ray on the camera and Geoffrey Attridge on colour photography. In 1978
Ralph Jacobson became the editor for the seventh edition, followed by the eighth edition in 1988 and
the ninth edition in 2000. He continued with the specialist contributions from these two authors and
others at the then Polytechnic of Central London (now the University of Westminster). The ninth
edition of 2000 and certainly this tenth edition must make it one of very few books to have a presence
in three centuries. It has come to be valued by many generations of photographers for the straightforward account it provides of both the theory and practice of photography as the technology has
evolved.
Sophie Triantaphillidou and Elizabeth Allen are the joint editors of this edition and under their
guidance have ensured that the manual remains true to its traditions. In the 10 years since the last

revisions were made to the manual there have been many significant technological developments.
This edition remains absolutely up to date with explanations of the principles of modern imaging
techniques. Like their predecessors they have enlisted the help of their colleagues with specialist
knowledge that ensures that the explanations remain both accurate and authoritative.
The previous edition saw a move away from traditional chemical-based photography to the now
widely practised electronically based imaging methods. This was in the era of hybrid imaging. Today
this is even more apparent with digital camera sales outstripping conventional analogue cameras by
around 100 to 1, excluding camera phones and one-shot single-use (recyclable) cameras. In order to
provide a balanced basis of modern photographic practice and keep the size of the book within
reasonable limits, the editors have been faced with difficult decisions on what to keep, what to discard
and what to add. Fortunately much of the core information applies as much to modern electronic

xv


Preface
systems as it does to analogue chemical systems. Optics and the basic physics of imaging are examples
of core areas which also appeared in previous editions. These core areas have been considerably
expanded to provide a sound basis for the understanding and practice of digital imaging. Surprisingly,
explanations of colour photography were only introduced in 1971, but since then have become
a significant topic in subsequent editions. This edition has four chapters devoted to this topic and
aspects of colour are of course embedded in other chapters where appropriate.
The move to digital imaging is now virtually complete, with conventional analogue or film-based
imaging now being practised by a relatively small number of photographers. This is reflected very
much in the content of this edition and arguments on the relative merits of the two approaches are
almost over as the quality obtainable by digital systems has exceeded all expectations. However, the
traditional chemical image-forming processes still have a smaller but significant presence in this
edition to cater for the needs of those dedicated users of this technology.
This edition is a completely revised book necessitated by the changes in imaging that have taken
place in the last 10 years.

The measurement of image quality both by physical means and by perception by observers has
been a key area for the development of all imaging systems. This is reflected in this edition by
specialist chapters dedicated to image quality and system performance, and important physical
aspects of image quality that include fundamental aspects of noise, sharpness, resolution and
information content. These considerations also apply to all imaging systems. Information on aspects
of modern digital imaging are extensively covered in specific chapters dedicated to sensors, cameras
and scanners, output media, file formats, image compression and image processing, workflow and
colour management systems.
The editorial team has made sure that this tenth edition remains true to the basic principles of their
predecessors in providing accessible and authoritative information on most technical aspects of
imaging.
Also, they have ensured that it remains of interest and value to anyone with an interest in imaging
systems who has a need for explanations of the principles involved in their practical applications.
Examples might include enthusiasts, students, professionals, technicians and computer users involved
in imaging.
Ralph Jacobson
Emeritus Professor of Imaging Science,
University of Westminster,
June 2010

xvi


Editors’
Acknowledgements
We are indebted to the previous editor of The Manual of Photography, our mentor and friend, Ralph
Jacobson, for his encouragement to undertake the authorship and editing of the current edition, for
his support during its production and his work as the technical editor. We would like to thank him
and the other authors from the previous edition, Geoffrey Attridge, Wally Axford, and Sidney Ray, for
allowing the use of parts of their text from the ninth edition. We are also grateful that two of these

previous authors have continued their contribution in this tenth edition and we thank them and our
new co-authors for their valuable input.
Thanks to Peter Burns for his contribution to technical editing; to Robert Hunt, Roy Berns, Mark
Fairchild, Phil Green and Andy Finney for allowing the use of data/figures/images from their
publications; to John Smith, Simon Brown and Andy Schonfelder for their assistance with research;
and to the Focal Press team for supporting this publication.
Lastly, but importantly we would like to thank Olivier, Jason, Anja and our parents.
Elizabeth Allen and Sophie Triantaphillidou

xvii


Author Biographies
Elizabeth Allen is a principal lecturer in Imaging Science at the University of Westminster. She
specialises in digital imaging systems and processes and image quality and has been the course leader
of the BSc Photography and Digital Imaging since 2005. Her work has been presented at a number of
symposia and has been published in related journals. She received the Selwyn Award from the Royal
Photographic Society in 2005 and is currently working towards a PhD in imaging science. She is also
a contributing author in the 7th and 8th editions of Langford's Advanced Photography.
Sophie Triantaphillidou is a principal lecturer and director of the Imaging Technology Research
Group at the University of Westminster. She received the Selwyn Award from the Royal Photographic
Society and her PhD in imaging science in 2001. She specialises in image quality, image archiving and
colour imaging. She has been the chair of the Imaging Science Group of The Royal Photographic
Society since 2007 and member of a number of conference programme committees related to imaging
science. She has published numerous research papers and is a contributing author in the 7th and 8th
editions of Langford's Advanced Photography.
Geoffrey Attridge has been an Emeritus Professor in Imaging Science at the University of Westminster,
since retiring in 2004 from over 30 years of teaching. He originally studied chemistry, obtaining a PhD
in chemical photography and during his early career worked at ILFORD laboratories. He is specialised
in sensitometry, chemical photography and colour imaging. He has authored and co-authored

prolifically, and has been a contributing author of the Manual of Photography since its 6th edition,
published in 1971. He served as the Chair of the Imaging Science Group of The Royal Photographic
Society between 2000 and 2006.
Efthimia Bilissi is a Senior Lecturer in imaging science at the University of Westminster, specialising in
imaging systems and image quality. She was awarded the Selwyn Award from the Royal Photographic
Society and gained her PhD in imaging science in 2004. Her work has been presented at many
national and international symposia and has been published in related journals. She is assistant
editor of the Imaging Science Journal and the editor and co-author of Langford's Advanced
Photography, 7th and 8th editions.
Robin Jenkin works as a Senior Engineer for Aptina Imaging Corp. in San Jose, helping to develop
image quality metrics by modelling, simulating and analysing imaging systems. He gained a PhD in
imaging science from the University of Westminster in 2002 and has since worked as a university
lecturer and researcher, publishing internationally in the field of image quality measurement. He
received a Fenton Medal from the Royal Photographic Society in 2007 and is currently the Executive
Editor of The Imaging Science Journal. Rob is additionally a Visiting Fellow in the field of ElectroOptics at Cranfield University and a keen practising photographer.
Sidney Ray was a Senior Lecturer at the University of Westminster from 1966 until retirement in 2004,
specialising in applied photography and photographic optics. He contributed to the four previous
editions of the Manual of Photography and has authored numerous books and papers on photographic topics. He has had numerous consultancies and roles in the professional practice of
photography and imaging and is an Honorary Fellow of both the British Institute of Professional
Photography and the Royal Photographic Society.

xviii


Chapter

|1|

Introduction to the imaging process
Elizabeth Allen

All images Ó Elizabeth Allen unless indicated.

INTRODUCTION
The second half of the nineteenth century saw the
progression from early experiments with light-sensitive
compounds to the first cameras and photographic films
becoming available to the general population. It developed
from the minority use of the camera obscura as a painter’s
tool, through the first fleeting glimpse of a photographic
image in a beaker containing silver compounds after light
exposure, to the permanent rendering of the image, and
then to the invention of the negativeepositive photographic process used today to produce an archival image.
A camera using roll film, the Kodak, was available to the
public in 1887 and brought photographic media to the
masses. By the beginning of the twentieth century, silver
halide materials were produced that were sensitive to all
visible wavelengths in the electromagnetic spectrum,
producing tonally acceptable images, and this paved the
way for practical colour imaging processes, beginning with
the Autochrome plate in 1907, to be developed.
Since this period, the ability to capture, manipulate and
view accurate images of the world around us has become
something that we take for granted. There are few places
in the world where images are not a part of daily life.
We use them to record, express, represent, manipulate and
communicate ideas and information. The diverse range of
applications for imaging leads to a multitude of functions
for the image: as a tool of coercion in advertising, a means
to convey a visual language or an aesthetic in art, a method
of visualization and analysis in science, to communicate

and symbolize in journalism, or simply as a means to
record and capture, and sometimes enhance, the experiences of everyday life. The manufacturing industries rely on

images for a multitude of purposes, from visualization
during the design and development of prototypes to the
inspection of manufactured components as part of industrial control processes. Photography and applied imaging
techniques using visible and non-visible radiation are
fundamental to some fields: in medicine for diagnosis and
monitoring of the progress of disease and treatment; and in
forensic science, to provide objective records in legal
proceedings and for subsequent analysis.
The art and science of photography and imaging has been
developed through multiple disciplines, as a result of
necessity, research and practice. The imaging process results
in an image that will be observed; therefore consideration of
the imaging chain, in practice or theory, must include the
observer. But the numerous functions of images mean that
the approach to and requirements from the imaging process
are various. If involved in the practice of imaging, however,
whatever the function of the image, it is impossible to avoid
the need to acquire technical skills and some knowledge and
understanding of the theory behind the imaging process.
Knowledge of factors affecting all stages of the imaging
chain allows manipulation of the final image through
informed selection of materials and processes. More
in-depth study of the fundamental science of imaging, as
well as being interesting and diverse, serves to enhance the
practical imaging process, as understanding can be gained of
the mechanisms involved, and processes and systems can be
characterized and controlled to produce required and

predictable results. Study of imaging science encompasses
the nature of light, radiometry and photometry, vision
science and visual perception, optics, colour science, chemistry, psychophysics, and much more besides. It provides
methodologies for the assessment of imaging systems and
tackles the complex issue of the evaluation of image quality.

Ó 2011 Elizabeth Allen & Sophie Triantaphillidou. Published by Elsevier Ltd. All rights reserved.
DOI: 10.1016/B978-0-240-52037-7.10001-8

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Chapter

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The Manual of Photography

The greatest change in our approach to imaging since the
development of the colour process has occurred in the last
25 years, with the burgeoning growth of digital imaging
technologies. The first consumer electronic camera system
was introduced to the public in 1981, but it took the
development of the personal computer, and its leap to
widespread use, before digital imaging became practical.
The internet has caused and facilitated an exponential
increase in image production and dissemination. Imaging
has grown to embrace computer science and computer
graphics in a symbiotic relationship in which each discipline uses elements of the others. Digital image processing
finds application in many areas from the aesthetic

enhancement of images to analysis in medical applications.
The immediacy of digital imaging has raised our expectations; it is likely that this, along with the efficiency of the
digital imaging process and the ease of manipulation of
digital images which are, after all, just arrays of numbers,
will mean that the traditional photographic process may
eventually be entirely replaced.
Keeping up with the changes in technology hence
requires the acquisition of different types of knowledge:
technical skills in computing for example, and an understanding of the unique qualities of information represented
by discrete data, in digital images, compared to the continuous representation of information, as used in analogue
(silver halide) imaging. It is clear that the need for new
practices and alternative approaches will continue as the
technology develops further. It is important, however, in
trying to understand the new technologies, not to forget
where it all started. Although technology has changed the
way in which we produce and view images, much of the
core science upon which the foundations of photography
were built remains important and relevant. Indeed, some
of the science has become almost more important in our
understanding of digital systems.

THE IMAGING PROCESS
The word ‘photography’ is etymologically derived from the
phrase ‘to draw with light’. Modern electronic imaging

Object

techniques are commonly classed under the umbrella term
‘digital imaging’ to distinguish between them and more
traditional silver halide photography; however, both

encompass the same core principle: the use of light to
produce a response in a light-sensitive material, which may
then be rendered permanent and viewed as an image of the
original scene. Detailed comparisons will be drawn
between the analogue and digital processes throughout this
book. Thus, an overview is presented below.
During image capture, light from a scene is refracted by
a lens and focused on to an image plane containing a lightsensitive material. Refraction is the deviation of a light ray as
it passes from one material to another with different optical
properties, and is a result of a change in its velocity as
it moves between materials of different densities (see
Chapters 2 and 6). The effects of refraction can be seen in
the distortion of an object when viewed from behind
a glass of water. Figure 1.1 illustrates the refraction of light
rays through a simple positive lens to produce an inverted
image in sharp focus on the image plane.
The amount of light falling on an image sensor is
controlled at exposure by a combination of aperture (the
area of the lens through which light may pass) and shutter
speed (the amount of time that the shutter in front of the
focal plane is open). This relationship is described by the
reciprocity equation: H ¼ Et, where E is the illuminance in
lux, t is the time of exposure and H is the exposure in
lux-seconds. At each exposure level, a range of possible
aperture ( f-number) and shutter speed combinations will
produce the same overall exposure. Choice of a particular
combination will affect the depth of field and sharpness/
motion blur in the final image. Traditionally a single
increment in the scale of possible values for both shutter
speed and aperture is termed a ‘stop’ (although many

cameras offer half-stop intervals). Each change of a single
stop in either aperture or shutter speed scale represents
a halving or doubling of the amount of light falling on the
sensor. The photometry of image formation is dealt with in
detail in Chapter 6 and exposure estimation is the subject
of Chapter 12.
Image formation occurs when the material changes or
produces a response in areas where exposed, which is in
some way proportional to the amount of radiation falling

Image
Plane

Optical Axis
Inverted Image

Figure 1.1 Image formation using a simple lens.

2


Chapter

1

Introduction to the imaging process

on it. In traditional photographic materials, exposed lightsensitive silver halide crystals (silver chloride, bromide or
iodide) form a latent image (see Chapter 13). Latent in this
context means ‘not yet visible’. The latent image is actually

a minute change on the surface of the exposed crystal,
where a small number of silver ions have been converted to
silver atoms, and is not visible to the naked eye. It is also
not yet permanent. In an image sensor electromagnetic
radiation falls on to pixels (a contraction of ‘picture
elements’), which are discrete light sensors arranged in
a grid. Each pixel accumulates charge proportional to the
amount of light falling on it.
After exposure, the image is processed. For simplicity we
consider the monochrome process, as colour is discussed in
more detail later in this chapter. In photographic chemical
processing the latent image is developed (Table 1.1).
During the development process silver halide crystals
containing latent image are reduced to metallic silver. The
silver forms tiny specks, known as photographic grains, and
these appear as black in the final image. The full range of
tones produced in a greyscale image is a result of different
densities of clusters of grains, and the image density in any
area is proportional to the amount of light that has fallen
on it. The image tones at this stage will be negative
compared to the original scene. After development time is
completed the material is placed in a stop bath to prevent
further development before the image is fixed.
In digital imaging, the processing will vary depending
upon the type of sensor being used (see Chapter 9). In a
charge-coupled device (CCD), the charge is transferred off
the sensor (‘charge coupling’), amplified and sent to an
analogue-to-digital converter. There it is sampled at discrete
intervals corresponding to individual pixels and quantized.
Quantization means that it is allocated a discrete integer

value, later to define its pixel value. The newer complementary metal oxide semiconductor (CMOS) image
sensors perform this image processing on the chip and
output digital values.

Table 1.1 Monochrome photographic process

PROCESS

OUTCOME

Exposure

Formation of latent image

Processing
Development

Latent image amplified and made
visible

Stop bath

Development stopped

Fixing

Unused silver halides converted into
soluble compounds which dissolve
in fixing agent

Washing

Soluble chemicals removed

Drying

Water removed

At this stage, the nature of the image represented by the
two systems is quite different. In silver halide materials,
the random arrangement of silver halide crystals in the
photographic emulsion means that a continuous range of
tones may be represented and silver halide methods are
often referred to as analogue imaging. The digital image,
however, is a grid of non-overlapping pixels, each of which
is represented by an integer number that corresponds to its
intensity. It cannot represent continuous tones in the same
way as silver halide materials because the data are discrete.
Various techniques, introduced later in this chapter, are
therefore used to simulate the appearance of continuous
tones.
The final step in the imaging process is image perpetuation, during which the image is rendered permanent. The
silver halide image is made permanent by fixation,
a process by which all remaining unexposed silver halide
crystals are made soluble and washed away. A digital image
is made permanent by saving it as a unique digital image
file. The image is then output in some way for viewing,
either as a print, a transparency or as a digital image on
a computer screen. In silver halide processes this involves
exposing the negative on to the print material and again

processing and fixing the image. A comparison of the
analogue and digital imaging processes is illustrated in
Figure 1.2.

IMAGE CONTROL
By careful control of every stage of the imaging process,
the photographer is able to manipulate the final image
produced. Image control requires an understanding of
the characteristics of imaging material and system,
composition, the behaviour and manipulation of light,
tone and colour, as well as the technical skill and ability
to combine all of these factors for the required result.
Such skills may be acquired by practice and experimentation, but having an understanding of the theory and
the science behind systems and techniques allows true
mastery of the process.

Control of image shape
When capturing an original scene, the photographer
controls composition of the image to be projected on to the
focal plane of the camera in a variety of ways. The format of
the camera selected (the size of the image sensing area) will
determine not only the design of the camera and therefore
the capabilities of the system, but also the size, quality and
aspect ratio of the final image. Large-format cameras (also
known as technical or view cameras, with an image format
of 5 Â 400 ) are designed to allow camera movements, physical
manipulation of the two planes containing lens and
imaging sensor separately, enabling the photographer to

3

Chapter

1

The Manual of Photography
Original scene

EXPOSURE

SILVER HALIDE NEGATIVEPOSITIVE PROCESS

IMAGE CAPTURE

CHARGE-COUPLED DEVICE
Exposed CCD

Exposed Film
Invisible latent image containing both exposed
and unexposed silver
halide crystals

IMAGE FORMATION

Charge accumulates
under pixels exposed to
light. No charge at
unexposed pixels

DEVELOPMENT
Digital Data

Film after Development
Developed image (silver
specks) and unchanged
silver salts

IMAGE PROCESSING

Response
proportional to light
exposure. Digital
values dependent
on bit depth of
system

CHARGE
TRANSFERRED OFF
CHIP, AMPLIFIED,
SAMPLED AND
QUANTISED

FIXATION
Film after Fixing

Pixel values in image file (8-bit)
Opaque
Developed image only a photographic
negative

IMAGE
PERPETUATION

Image file contains
header and digital
data (as a
minimum)
Examples: TIF,
JPEG, RAW, PSD

255 255 255 255 255
255 0

0

0 255

255 0

0

0 255

255 0

0

0 255

255 255 255 255 255
255 255 255 255 255

Transparent

IMAGE OUTPUT
IMAGE PRINTED TO
PRODUCE POSITIVE

Image

PIXEL VALUES
CONVERTED TO
COLOUR VALUES IN
DESTINATION COLOUR
SPACE, TO BE USED BY
OUTPUT DEVICE FOR
COLOUR OUTPUT

Figure 1.2 Analogue and digital imaging processes.

change the size, magnification and perspective of elements
on the plane of sharp focus. Image viewpoint is one of the
key factors influencing composition, as this controls not
only the positioning of different subjects and the perspective within the scene (the relationship between relative size
and position of objects), but also whether the image is in

4

portrait or landscape format (if using a rectangular image

format). Chapter 11 covers camera movements and camera
systems in detail.
Image shape is also controlled by the focal length of the
lens being used. In a simple positive lens the focal length is
the distance from the lens to the rear principal focus, defined


Chapter

1

Introduction to the imaging process
Focal Plane

Compound Lens

Angle of view

Image Diagonal
Focal Length, f

Figure 1.3 Angle of view of a lens.

as the point on the optical axis at which the lens brings
a distant object to sharp focus. The focal length is determined by the curvature, thickness and refractive indices of
optical components, and this in turn defines the angle by
which light rays are deviated (refracted) as they pass
through them. This determines the field angle of view, as
illustrated in Figure 1.3. Geometric optics is the subject of
Chapter 6.

The angle of view determines the amount of the original
scene covered by the lens. Standard lenses for each format
have an angle of view of around 50 . Wider angle lenses
have shorter focal lengths and cover more of the original
scene, hence often displaying distortion around the
periphery of the image. Longer focal lengths cover a much
smaller area of the original scene and may therefore show
less off-axis curvilinear distortion.

Depth of field
Depending upon the lens focal length, there is a point of
optimum focus in a scene that will be a particular distance
away (depth) from the camera and will produce a sharp
image exactly at the focal plane. There are also zones in
front of and behind this point that will produce acceptably
sharp images. This zone of sharp focus is referred to as
depth of field and can be an important aspect of composition. A shallow depth of field will contain a small range of
planes of sharp focus, all other planes being out of focus,
hence isolating and emphasizing a subject of interest.
Depth of field is influenced by lens focal length, distance to
focused object, and also lens aperture.

Tone and contrast
As well as the position and size of scene elements, the
photographer may also influence the composition by
controlling the tone and colour of elements relative to each
other. Tone in the original scene is defined by the intensity
of light reflected from an object. The tone and contrast of
the scene and reproduced image may be manipulated in

a variety of ways, for aesthetic purposes, or to work within
the limitations of a device or system.

Lighting control in the original scene
When white light reaches a surface, some wavelengths are
absorbed and some are reflected or transmitted. Tone is
controlled by the surface properties of the subject and the
nature and intensity of the light source illuminating it. The
contrast of the scene is the ratio between the brightest and
darkest tones in the scene and the range of possible
intensity levels in between, and may be controlled or
manipulated at a number of stages in the imaging chain.
Again, this is affected by the absorption characteristics of
the surfaces being illuminated, but also by their position
relative to the scene illuminants. Therefore the photographer can use lighting techniques to change image contrast.
By adding light sources or changing the angle or distance of
subjects relative to illuminants, the difference between
highlight and shadow can be compressed or expanded.
The tone reproduction of a device or material describes
how the range of intensities in the original scene is mapped
to those in the final image (see Chapter 21). Tone reproduction is limited by many factors in the imaging chain,
including the dynamic range of the image sensor e that is, its
ability to record and represent a range of densities or
intensities. Dynamic range in silver halide materials is also
dependent upon exposure level. Selection of a particular
type of film or image sensor will influence the range of
possible tones at capture. Because both photographic and
digital imaging processes involve an imaging chain
containing multiple stages and devices, there are a number
of points after image capture in which tone reproduction

may be manipulated. Developing agents used in photographic processing, setting up and calibration of output
devices, and selection of printing materials and processes
all help to define the range of tones possible in the output
image. Digital image processing software makes tonal
adjustment simple and interactive through manipulation
of image tonal curve or histogram.

5


Chapter

1

The Manual of Photography

Colour
Colour imaging involves an analysis stage in which the
response of a sensor to narrow bands of wavelengths is
recorded; it is followed by a synthesis stage, where the
measured values are converted to a response in an output
device, to produce a colour that matches to a certain degree
the visual appearance of the original. The rendition of
colour in an image, whether digital or analogue, is
dependent upon a variety of factors. The complex mechanisms by which the human visual system perceives colour
mean that no colour reproduction will be identical to the
colours perceived in the original scene. The aim in colour
reproduction is to produce consistent and acceptable
colour, and is influenced by colour preference and
‘memory colours’, which are often quite different to the

actual colour qualities of associated subjects. Fundamental
colour science is introduced in Chapter 5. Colour reproduction is the subject of Chapters 22 and 23.
The colours recorded from an original scene are
a combination of the wavelengths present in the illuminant
(the spectral power distribution) and the spectral reflectance characteristics of the surface on which the light
falls, coupled with the spectral responsivity of the sensor.
Choice of light source and appropriate sensor are therefore
important factors in determining final colour quality of the
image. The wavelengths reaching the sensor can be altered
by filtering the light sources using coloured ‘gels’ or using
optical filters over the lens.
Colour reproduction through the imaging chain is
managed by the selection of appropriate reproduction
materials and devices. In photographic imaging, colour is
manipulated by filtration at the capture stage (through the
use of different colour-sensitive layers in emulsions) and
also at the output stage (by filtration during printing).
Digital image processing provides a powerful tool in the
processing of colour in digital images, allowing simple
manipulation of global colour balance, specific ranges of
colours, or localized areas within the image. The many
different stages in the digital imaging chain and the diverse
range of devices and technologies available mean that
colour translation between devices is complicated. The
colour gamuts of input and output devices are highly device
dependent, meaning that the same pixel value may
produce different colours on different devices, depending
upon their characteristics and age, and the way they are set
up and calibrated.
This problem has led to the development of colour

management systems (see Chapter 26), which manage the
process of converting pixel values into the output colour
values of different devices. To gain a proper understanding
of digital colour management, a continually evolving
discipline, requires some knowledge of colour science, the
nature of light and the human visual system. Colour
management relies on the absolute specification of colour
as the human visual system perceives it. This specification

6

(CIE colorimetry) is based upon experiments performed
using human observers in 1931, many years before the
extent of digital imaging today could be truly imagined.
While colour management in a photographic system
involves an understanding of colour filtration and the
colour reproduction characteristics of a particular slide film
or film/paper combination, digital colour management
involves the careful calibration and characterization of all
input and output devices coupled with an understanding of
the different digital representation of colour through the
imaging chain, and software to perform colour processing.

THE ORIGINS OF PHOTOGRAPHY
Camera obscura
Since the development of systematic schools of philosophy
in Ancient Greece in around 500 years BC, man has found
enduring fascination in attempting to understand the
nature of light and its behaviour. In China at around this
time, Mo Tzu, considered one of the first great Chinese

philosophers, emphasized the importance of pragmatism
in philosophical thought. His followers began measuring
and observing the behaviour of light using flat and curved
mirrors. It is believed that they also discovered the camera
obscura, which was later further developed by Alhazen
(AD965), a mathematician and physicist born in Basra,
Iraq. The camera obscura produced the first projected
images of the real world and may therefore be viewed as the
starting point for photography. Camera obscura literally
means ‘dark chamber’. When light passes from outside
a light-tight chamber or box through a pinhole, an inverted
image is formed on the opposite surface. By the seventeenth century, the camera obscura had been adapted by
placing a lens in front of the aperture and portable versions
became a tool for painters, allowing them to accurately
trace landscapes.

Early experiments
It was natural that the emphasis on developments in science
and technology in Europe during the time of the Industrial
Revolution (beginning in Britain in the latter part of the
eighteenth century) would lead to attempts to try to
‘capture’ light and obtain a permanent image using the
camera obscura. In 1727, Johann Heinrich Schulze,
a German university professor, had discovered that light
exposure caused silver nitrate to darken; this was an
important step forward in the search for a light-sensitive
material. In 1777, the Swedish chemist Karl Wilhelm
Scheele observed the same effect using silver chloride.
Thomas Wedgwood (1771e1805), son of Josiah, the
famous potter, and Sir Humphrey Davy experimented with

the use of paper soaked in silver nitrate placed in the camera