Physics of Digital Photography

by Andy Rowlands

Overview

Physics is fundamental to all aspects of digital photography. This book works through the photographic imaging chain starting from the physics of image capture through to the conversion of the raw data into a viewable image. The author’s aim is to show how knowledge of the underlying physics can be used by a photographer or imaging scientist to maximise the technical quality of the final image. With the increasing use of digital photography in a research environment scientists and engineers need to better understand the science behind digital photography to fully exploit this tool in their research. As well as an academic readership, this book will be of interest to professional and serious amateur photographers wanting a better understanding of the technical aspects of digital photography.

Product Details

ISBN-13:	9780750312431
Publisher:	Iop Publishing Ltd
Publication date:	06/29/2017
Pages:	329
Product dimensions:	7.33(w) x 10.53(h) x 0.96(d)

About the Author

Andy Rowlands obtained a first class degree in Mathematics and Physics from the University of Warwick in 2000 followed by a PhD in Physics in 2004. He was subsequently awarded an EPSRC Fellowship in Theoretical Physics in the field of condensed matter theory at the University of Bristol and later he worked at Lawrence Livermore National Laboratory in the USA. In 2009 he took a sabbatical from physics and moved to China to pursue his interest in photography, during this time he became interested in the application of physics to photography. Returning to physics he took up a postdoctoral position at Tongji University in Shanghai. An extensive knowledge of the theoretical concepts involved and practical experience as a free-lance photographer puts the author a unique position to develop this text.

Table of Contents

Preface xiii

About the author xiv

Acronyms xv

1 Fundamental optical formulae 1-1

1.1 Image formation 1-2

1.1.1 Refraction 1-2

1.1.2 Gaussian optics 1-3

1.1.3 Lens refractive power 1-8

1.1.4 Magnification 1-13

1.1.5 Focal length 1-14

1.1.6 Lens focusing movement 1-17

1.2 Field of view 1-21

1.2.1 Entrance and exit pupils 1-22

1.2.2 Chief and marginal rays 1-23

1.2.3 Angular field of view 1-24

1.2.4 Field of view area 1-28

1.2.5 Focal-length multiplier 1-29

1.3 Depth of field 1-30

1.3.1 Circle of confusion 1-30

1.3.2 Depth of field equations 1-32

1.3.3 Hyperfocal distance 1-37

1.3.4 Focus and recompose limits 1-38

1.3.5 Keystone distortion 1-40

1.4 Exposure 1-42

1.4.1 Photometry 1-43

1.4.2 Flux emitted into a cone 1-44

1.4.3 Relative aperture 1-47

1.4.4 F-number 1-49

1.4.5 Working f-number 1-50

1.4.6 F-stop 1-52

1.4.7 Natural vignetting 1-52

1.4.8 Photometric exposure 1-54

1.4.9 Exposure value 1-56

1.4.10 F-number for aplanatic lenses 1-57

Bibliography 1-61

2 Exposure strategy 2-1

2.1 Digital output 2-2

2.1.1 Sensor response 2-2

2.1.2 Colour 2-3

2.1.3 Digital output levels 2-4

2.1.4 Dynamic range 2-5

2.1.5 Tonal range 2-7

2.1.6 Tone reproduction 2-7

2.1.7 Gamma 2-8

2.1.8 Tone curves 2-14

2.1.9 Histograms 2-16

2.2 Average photometry 2-17

2.2.1 Reflected-light metering 2-18

2.2.2 Meter calibration 2-19

2.2.3 Average scene luminance 2-22

2.3 Exposure index 2-23

2.3.1 ISO speed 2-24

2.3.2 Standard output sensitivity 2-27

2.3.3 Recommended exposure index 2-29

2.3.4 Extended highlights 2-29

2.4 Exposure modes 2-31

2.4.1 Metering modes 2-31

2.4.2 Exposure compensation 2-32

2.4.3 Aperture priority (A or Av) 2-32

2.4.4 Shutter priority (S or Tv) 2-33

2.4.5 Program mode (P) 2-34

2.4.6 Manual mode (M) 2-34

Bibliography 2-35

3 Raw data model 3-1

3.1 Linear systems theory 3-2

3.1.1 Radiometry 3-3

3.1.2 Ideal image 3-5

3.1.3 Point-spread function (PSF) 3-6

3.1.4 Convolution 3-7

3.1.5 Optical transfer function 3-12

3.1.6 Modulation transfer function (MTF) 3-13

3.1.7 Phase transfer function 3-15

3.1.8 Model camera system 3-16

3.2 Optics 3-17

3.2.1 Wave optics 3-17

3.2.2 Huygens-Fresnel principle 3-20

3.2.3 Aperture diffraction PSF 3-21

3.2.4 Circular aperture: Airy disk 3-27

3.2.5 Aperture diffraction MTF 3-29

3.2.6 Wavefront error 3-31

3.2.7 Polarisation 3-34

3.3 Sensor 3-39

3.3.1 Irradiance spatial integration 3-39

3.3.2 Detector-aperture PSF 3-40

3.3.3 Detector-aperture MTF 3-42

3.4 Optical low-pass filter 3-44

3.4.1 Sampling theorem 3-44

3.4.2 Sensor Nyquist frequency 3-48

3.4.3 Pre-filtering 3-50

3.4.4 Four-spot filter PSF 3-50

3.4.5 Four-spot filter MTF 3-51

3.5 Real image 3-52

3.5.1 System PSF 3-53

3.5.2 System MTF 3-54

3.6 Sensor signal 3-55

3.6.1 Charge collection 3-55

3.6.2 Colour filter array 3-58

3.6.3 Spectral responsivity 3-58

3.6.4 Polychromatic PSF and MTF 3-60

3.7 Analog-to-digital conversion 3-61

3.7.1 Charge detection 3-61

3.7.2 ISO gain 3-62

3.7.3 Digital numbers 3-63

3.7.4 Conversion factor 3-63

3.7.5 Bias offset 3-65

3.8 Noise 2-65

3.8.1 Temporal noise 3-66

3.8.2 Fixed pattern noise 3-67

3.8.3 Noise measurement 3-68

3.8.4 Noise models 3-70

Bibliography 3-74

4 Raw conversion 4-1

4.1 Reference colour spaces 4-2

4.1.1 Physics of colour 4-2

4.1.2 Standard colourimetric observer 4-3

4.1.3 CIE RGB colour space 4-7

4.1.4 Chromaticity diagram (rg) 4-8

4.1.5 CIE XYZ colour space 4-9

4.1.6 Chromaticity diagram (xy) 4-11

4.1.7 Absolute colourimetry 4-13

4.1.8 Relative colourimetry 4-14

4.1.9 Reference white 4-14

4.2 Illumination 4-15

4.2.1 Colour temperature 4-15

4.2.2 Correlated colour temperature 4-15

4.2.3 White point 4-17

4.2.4 Standard illuminants 4-17

4.3 Camera raw space 4-18

4.3.1 Eye response functions 4-18

4.3.2 Camera response functions 4-20

4.3.3 Luther-Ives condition 4-22

4.3.4 Demosaicing methods 4-23

4.3.5 Camera colour characterisation 4-24

4.4 sRGB colour space 4-27

4.4.1 sRGB gamut 4-27

4.4.2 sRGB gamma 4-29

4.4.3 sRGB dynamic range 4-31

4.4.4 sRGB colour cube 4-31

4.5 White balance 4-32

4.5.1 Adopted white 4-34

4.5.2 Chromatic adaptation transforms 4-36

4.5.3 White balance strategies 4-39

4.6 Example 1: Adobe® DNG (raw to XYZ D50) 4-42

4.6.1 Method 1 (transformation matrix + CAT) 4-43

4.6.2 Method 2 (raw WB multipliers + forward matrix) 4-47

4.7 Example 2: dcraw (raw to sRGB D65) 4-52

4.8 Image editing 4-59

4.8.1 Colour management 4-59

4.8.2 Adobe® Photoshop® colour settings 4-61

4.8.3 Image resizing 4-65

Bibliography 4-67

5 Image quality 5-1

5.1 Perceived resolution 5-3

5.1.1 Observer resolving power 5-3

5.1.2 Circle of confusion specification 5-4

5.2 Cross-format comparisons 5-9

5.2.1 Equivalence ratio 5-10

5.2.2 Equivalence at infinity focus 5-11

5.2.3 Equivalence at arbitrary focus 5-15

5.2.4 Summary of equivalence 5-23

5.3 Lens MTF 5-25

5.3.1 Aberrations 5-25

5.3.2 Lens MTF plots 5-26

5.3.3 Lens MTF and sensor format 5-30

5.3.4 Lens resolving power 5-31

5.4 System MTF 5-34

5.4.1 System MTF and sensor format 5-34

5.4.2 System resolving power 5-35

5.5 Sharpness 5-36

5.5.1 Sharpness metrics 5-38

5.5.2 Image resampling 5-41

5.5.3 Diffraction softening 5-46

5.6 Signal-to-noise ratio 5-49

5.6.1 SNR and ISO setting 5-51

5.6.2 Shadow improvement 5-55

5.6.3 ISO invariance 5-56

5.6.4 SNR and pixel count 5-57

5.6.5 SNR and sensor format 5-59

5.7 Dynamic range 5-59

5.7.1 Engineering dynamic range 5-59

5.7.2 Photographic dynamic range 5-61

5.8 Practical strategies 5-63

5.8.1 Object resolution 5-64

5.8.2 Non-destructive noise reduction 5-66

5.8.3 Exposing to the right 5-68

Bibliography 5-72