Nature Science+Photography Volume 4: Contrast
Volume 4 of the series Nature Science+Photography explores the subject of contrast:
What is contrast, and how is it determined?
Why is contrast crucial to our visual perception?
What is the contrast sensitivity of the visual system, and on what factors does it depend?
How many tonal values can we perceive in a photograph?
What expectations do we have regarding the contrast reproduction of a photograph?
How do we meet these expectations in analog and digital photography?
On what does the contrast capacity of our image media depend?
What is gamma correction all about?
What role does contrast play in exposure metering?
Chapter 1 lays the essential groundwork by exploring the concept of contrast itself: what we actually
mean by the term, why photographic engineers rely so heavily on logarithmic scales, the difference between
global and local contrast, objective measurement methods (Michelson, RMS, etc.), and the crucial idea of dynamic
range—both in scenes and in recording media.
Chapter 2 shifts the focus to human perception, explaining why contrast is not a minor detail but the single most
important carrier of visual information for our species. Our visual system does not faithfully reproduce luminance
ratios; instead, it constructs the perceived world almost entirely from discontinuities—edges—because that
is the most neurologically efficient way to encode a complex environment with limited bandwidth. Readers
will encounter the contrast sensitivity function (CSF), the role of spatial frequency, the effects of surround
brightness (simultaneous contrast, Crispening effect), and adaptation mechanisms that operate over many
orders of magnitude.
Chapter 3 brings everything back to the photographer’s hands. It begins by articulating the largely unspoken
expectations we carry into every image: that highlights should feel open yet retain micro-contrast,
that shadows should remain detailed without appearing unnaturally light, that midtones should exhibit snap
and three-dimensionality. We then examine how traditional silver-halide films—especially chromogenic negative
and reversal materials—were empirically evolved over a century to match these perceptual expectations
almost serendipitously. Digital sensors, by contrast, follow fundamentally different physics: linear encoding,
fixed saturation wells, read noise, and photon-shot-noise dominance at low signal levels produce a
characteristically different contrast behavior. The chapter details how to measure a sensor’s actual electro-optical
transfer function, how tone curves and “film simulations” attempt to bridge the gap, and practical strategies
for meeting subjective imagequality goals in a digital workflow.
The closing sections tackle two perennial sources of confusion: why correct digital exposure prioritizes highlight
protection over the old “expose for the shadows” mantra of film, and the expanded possibilities—but also pitfalls—
of contrast manipulation at the moment of capture (multiple exposures, graduated filters, in-camera HDR, etc.).
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Content
Introduction 5
1. What contrast is and how to determine it
Definition 8
The logarithm 10
...in mathematics 10
...in photography 11
The characteristic curve 12
Contrast measures - The gamma value 15
Contrast measures - The beta value 16
Contrast measures - The contrast index 17
The dynamic range 18
2. Contrast perception
Why contrast is crucial to our visuality 20
The dynamic range of the visual system 21
The response range of the photoreceptors 22
The light/dark adaptation 23
Lateral inhibition 26
Dynamic amplification 28
Pupil size 28
The minimum size of brightness differences 29
The number of perceptible tonal values 32
3. Contrast in photography
Demand 0 - Our expectations from the contrast reproduction of a photograph 36
Factors to consider - Stray light 37
Factors to consider - Ambient brightness 40
Factors to consider - Image quality 41
The resulting characteristic 42
Demand 0 in analog photography 42
Practical consideration reversal film 46
Practical consideration negative film plus paper 47
The contrast behavior of electronic image carriers 48
The dynamic range of electronic image carriers and the limiting factors 53
The lower limit of the dynamic range - Noise 53
Readout noise 53
Shot noise 54
Fixed-pattern noise 54
Random pattern noise 55
Dark noise 55
The upper limit of the dynamic range - Maximum signal 55
ISO setting 55
Full Well Capacity 56
Determining the dynamic range of a digital imaging system 57
Encore - The bit width of the A/D conversion
and its relationship to the dynamic range 61
Practical consideration of the variables dynamic range, sensitivity, full well capacity and pixel area 62
Demand 0 in the digital area 64
Compensation of stray light 64
Compensation of ambient brightness 65
Increase of image quality 65
Gamma correction - 1. Distorting linearity 69
Gamma correction - 2. Compensating the monitor properties 71
Gamma correction - 3. Distribution of brightness values on 8 bit 73
Gamma values in different color spaces 77
Contrast and exposure 78
12% or 18% - The problem of the calibration value of the exposure meters 80
Color brightness and exposure metering 81
Possibilities of exposure metering - Object metering 83
Integrative measuring methods 84
Selective measuring methods 87
Possibilities of exposure metering - Light metering 89
Exposure determination for silver film 90
Exposure determination for digital recording systems 90
4. Appendix 96
Jörg Sczepek
Nature Science+Photography
Volume 4: Contrast
6.69x9.61" / 17x24.5 cm
78 color images, 101 pages, 12.99 $
ISBN 9798248956739
Independently published
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