3.0 VISUAL PERCEPTION AND COLOR🔗⧉

A white shirt still looks white as you carry it from daylight into a room lit by warm bulbs, although the spectrum reaching the eye changes. A small patch can also look lighter or darker when only its surroundings change. To predict how a photograph will appear, we need more than a measurement of its pixels.

Chapter 3.1, The eye and image formation describes the optics and receptor mosaic. Chapter 3.2, Perceptual color and trichromatic vision explains why different spectra can produce the same color match. Chapter 3.3, Adaptation and constancy considers changes in illumination and context; Chapter 3.4, Spatial and temporal vision describes sensitivity to detail and flicker. Chapter 3.5, The visual system attends little and makes things up examines attention and visual inference, and Chapter 3.6, Animal eyes compares other ways of sensing the world.

These properties guide color reproduction, tone mapping, display design, and compression. Their predictions depend on the observer and viewing conditions. Part 4, Color spaces and color technology develops the corresponding measurements and engineering tools.

The physical stimulus and its appearance are different descriptions. A spectrum becomes a color measurement only after we specify an observer, and the appearance also depends on adaptation and spatial context. This is why understanding the observer belongs beside understanding the sensor. It explains engineering choices such as white balance, chroma subsampling, and allocating precision to tones the eye can distinguish.

Contents of this part

• 3.1 The eye and image formation
• 3.2 Perceptual color and trichromatic vision
  • 3.2.1 Cone photoreceptors and perceptual color
  • 3.2.2 Metamers
  • 3.2.3 Color blindness
  • 3.2.4 Opponent process and the multistage model
  • 3.2.5 So what are the primary colors?
  • 3.2.6 Color as linear algebra
• 3.3 Adaptation and constancy
  • 3.3.1 Light adaptation
  • 3.3.2 Visual perception is largely invariant to multiplications
  • 3.3.3 Contrast
  • 3.3.4 Lightness constancy
  • 3.3.5 Color constancy
• 3.4 Spatial and temporal vision
  • 3.4.1 Spatial vision
  • 3.4.2 Chrominance spatial vision
  • 3.4.3 Temporal vision
• 3.5 The visual system attends little and makes things up
  • 3.5.1 Attention and eye movements
  • 3.5.2 The visual system makes things up
• 3.6 Animal eyes
  • 3.6.1 The optics: many ways to form an image
  • 3.6.2 The pupil: aperture shape as a clue to ecology
  • 3.6.3 Amphibious vision: focusing in air and in water
  • 3.6.4 The sensor: a retina that is not uniform
  • 3.6.5 Seeing in the dark: sensitivity and its tricks
  • 3.6.6 Acuity: the finest detail, and how to sharpen it
  • 3.6.7 Color vision: opsins remixed
  • 3.6.8 Polarization: the axis we are blind to
  • 3.6.9 Temporal vision: flicker, and motion first
• 3.7 Human vision TLDR
  • 3.7.1 The eye is a camera with an uneven sensor
  • 3.7.2 Three cones reduce a spectrum to three numbers
  • 3.7.3 Primaries are a choice, and the axes are skewed
  • 3.7.4 Color blindness is a missing or shifted axis
  • 3.7.5 After the cones, brightness and two color differences
  • 3.7.6 The eye works on ratios, not levels
  • 3.7.7 The eye reports surfaces, not light
  • 3.7.8 Spatial vision is band-pass, and measured in degrees
  • 3.7.9 Color detail is coarser than brightness detail
  • 3.7.10 Vision has a finite temporal bandwidth
  • 3.7.11 Vision is foveal, serial, and partly invented
  • 3.7.12 What the rest of the book does with this

▸ full collapsible outline of this part