Forensic Photography

Forensic photography plays a vitally important part in the
investigation of crime and the subsequent administration of
justice. Written by a practitioner with many years professional
experience, this book provides an overview of the most common
forensic photography techniques in use today for those readers who
may not have a detailed understanding of camera techniques and who
need to get to grips with the use of light and other key scientific
aspects of the job. It covers image capture issues, file handling
and relevant equipment, such as lasers and UV lights, and explores
how they work.

The predominance of the digital camera has resulted in an
increasing trend for police forces across the world to use
untrained camera users, rather than expert photographers.
Therefore, this book will prove invaluable for those practitioners
who need to produce accurate and clear photographic evidence, above
and beyond the point and shoot mode on their cameras.

Auteur

Nick Marsh is the author of Forensic Photography: A Practitioner's Guide, published by Wiley.

Résumé

Forensic photography plays a vitally important part in the investigation of crime and the subsequent administration of justice. Written by a practitioner with many years professional experience, this book provides an overview of the most common forensic photography techniques in use today for those readers who may not have a detailed understanding of camera techniques and who need to get to grips with the use of light and other key scientific aspects of the job. It covers image capture issues, file handling and relevant equipment, such as lasers and UV lights, and explores how they work.

The predominance of the digital camera has resulted in an increasing trend for police forces across the world to use untrained camera users, rather than expert photographers. Therefore, this book will prove invaluable for those practitioners who need to produce accurate and clear photographic evidence, above and beyond the point and shoot mode on their cameras.

Contenu

Foreword xi

Preface xiii

Acknowledgements xix

About the Companion Website xxi

1 Image Processing 1

1.1 Introduction 1

1.2 The digital image 2

1.3 Image acquisition 3

1.4 Colour images 4

1.5 The imaging chain and workflow 5

1.6 White balance 7

1.7 Image histogram 8

1.7.1 Levels and grey-picker tools 8

1.8 Image processing terminology 12

1.9 Digital image processing operations 14

1.9.1 Image cropping 14

1.9.2 Image resampling (resizing) 15

1.9.3 Image flipping and rotation 15

1.9.4 Linear scales 17

1.10 Classes of operations 19

1.10.1 Point processing 19

1.10.2 Addition 19

1.10.3 Subtraction 19

1.10.4 Multiplication and division 20

1.10.5 The bad news: artefacts 22

1.10.6 The good news: versatility 22

1.11 Noise reduction 22

1.12 Sharpening filters 24

1.13 History log 27

1.14 Layers 27

1.14.1 Adjustment layers and layer masks 27

1.14.2 Composite images 28

1.15 Bit depth and dynamic range 28

1.16 File formats 29

1.17 Image compression 29

1.18 Image processing at image capture 30

1.19 Properties of common formats 31

1.20 Image archiving and the audit trail 32

1.20.1 Best practice and the audit trail 33

1.21 Printing images 35

1.22 Image storage 35

1.23 Summary 35

2 Cameras and Lenses 37

2.1 Overview 37

2.2 Cameras 40

2.3 Exposure 43

2.4 ISOs 45

2.5 The shutter 46

2.6 F-stops and apertures 47

2.7 So what is the correct exposure? 49

2.8 Metering modes 50

2.8.1 Measuring the light 50

2.8.2 Camera meters 51

2.8.3 Incident light meters 51

2.9 Getting the right exposure 51

2.10 Dynamic range 52

2.11 Depth of field and focus 53

2.11.1 Lens choice 55

2.11.2 Distance to the subject 56

2.11.3 The rule of thirds 56

2.11.4 Focus 56

2.11.5 Manual focus 58

2.12 Lenses 65

2.12.1 Focal lengths 67

Reference 77

3 The Use of Flash 79

3.1 How does it work? 79

3.2 Guide numbers 81

3.2.1 What is the guide number? 81

3.3 Flash modes 83

3.3.1 Manual mode 83

3.4 The inverse square law (ISL) 90

3.4.1 The ISL (long version) 90

3.4.2 The ISL short version 92

3.4.3 Automatic 92

3.4.4 Through The Lens metered flash (TTL) 93

3.4.5 Other settings 94

3.5 The practical application of flash 95

3.5.1 Flash only 95

3.5.2 Open flash 99

3.5.3 Fill in flash 105

3.6 Types of flash 108

3.6.1 Hammerhead units 108

3.6.2 Ring flash 108

3.6.3 Semi ring flashes 109

3.6.4 Studio flash 110

4 Crime Scene Photography 113

4.1 Overview 113

4.1.1 What are we being asked to photograph? 114

4.1.2 When do I take photographs? 114

4.1.3 How will I take the photographs? 115

4.2 Personal protective equipment (PPE) 115

4.2.1 Stepping plates 118

4.3 The generics of scene photography 119

4.3.1 Sunshine 119

4.3.2 Rain 121

4.3.3 Wind 121

4.3.4 Fog 122

4.3.5 Snow 122

4.3.6 Cold 122

4.4 Photographic equipment 123

4.5 Composition 124

4.5.1 Interiors 130

4.6 Specific types of scenes 134

4.6.1 Motor vehicles 138

4.6.2 Assault victims 145

4.6.3 Prisoners 146

4.6.4 Property 147

4.6.5 Fire damaged scenes 149 4.6.6 RTC (Road Traffic Collision...