Color Categories in Thought and Language. Hardin, Maffi (eds). Book 1997.

Chapter 3: The Psychophysics of Color (Wooten, Miller)

  1. Having just two photopigments wouldn’t allow for the sort of color differentiation people have (1 just allows mono of course)
  2. On the other hand, In 1803 Thomas Young (later Young Helmholtz theory) noted that if we had many different photopigments, we would have problems with spatial vision
  3. The compromise is 3 – still not perfect color differentiation of course, but works well for our needs
  4. Understanding the basic system of photopigments explains much about color vision
  5. So Helmholtz thought we had receptors for R,G,B but 19th century physiologist Hering asked, how can you get yellow from additive R,G,B?  You can’t.  He proposed the opponent-process model
    1. 4 primary hue sensations: RGB+yellow, and G is blue and yellow
    2. Furthermore, we can see blue, and green-blue, and red-blue, but there is no such thing as yellow-blue.  Likewise, green can go with Y or B but not R
    3. Based on these observations, proposed that yellow and blue are opposites in an opposing process, likewise for red, green
    4. What we see is based on how these two separate opposed processes react
  6. White is activated directly by stimulation, but black is only by contrast when there is nearby stimulation
  7. When R/G, Y/B channels are in equilibrium, only Bk and W channels are excited giving black, grey, white.
    1. But most stimuli don’t produce perfectly balanced chromatic channels, as well as Bk and W.  Simultaneous activation of chromatic and achromatic leads to perception of saturation, where pure red is at one end (for example) and pure black or white at the other, with maroon or pink respectively in between
  8. Although still not proven, single cell recordings seem to confirm Hering’s proposal, and there are opponent color cells.
  9. It turns out both camps were right in a way – there are three types of receptors as Young-Helmholtz predicted, but the way they relate to each other was according to Hering’s model pigment function is as follows:
    1. alpha: -B, +R
    2. beta: +Y, -G
    3. gamma: +Y, +R
  10. In 1955, Jameson, Hurvich quantified Hering’s formulation with algebraic expressions.  The idea is that ‘redness’ can be described as how much green must be added to make the color appear neither red or green (likewise for Y/B)
  11. They then ran experiments asking what % of RGBY they saw in monochromatic light <how could it be monochromatic then??>  Subjects quickly found the task easy and reported red-greens or yellow-blues.  The numbers closely matched those that were predicted by the model (96%, although accuracy was still increasing by the end of the experiment so probably is even higher)
    1. There is also, however, some indication of nonlinearities in the actual data, but the model is strictly linear. Still, its pretty accurate
  12. Everyone has different “elemental” (think “primary” although slightly different meaning, as elemental also includes Bk/W) colors.  What each person would define as perfect Y with no R or G differs.
  13. Further experiments had subjects verbally describe colors based on a restricted set of color names.  A color term is sufficient and necessary to describe a color if it is elemental.  Given a set of terms, the set is sufficient if it can be used to describe any color.  If a color term is necessary and is excluded from the set, then not all stimuli can be described fully
    1. For example, if unable to respond yellow, when presented with a yellowish color, and the only response is 25% red, then the incomplete description (need another 75%) means the terms available weren’t adequate
    2. By these means, it was determined orange was not fundamental because it was described successfully with Y,R
  14. In the Munsell system, there is an implied elemental purple because it is given equal status in the color wheel with the 4 elemental colors – the above experiment however, showed that purple also was not elemental
  15.  Brightness is not the same as lightness and ranges from dim to bright, encoding stimulus intensity
  16. Experiments on monochromatic color require use of 2 stimulus fields to create contrast, this is most commonly done experimentally as a disc surrounded by a ring of another neutral light
    1. This experiment showed grey not elemental, while white black are
  17. Later, there were quantitative versions of these experiments where 4 hue terms were given along with a saturation judgement

Chapter 8: Color Systems for Cognitive Research

  1. The common way to measure the number of colors we can recognize is to put two blocks of the same color adjacent to each other and then vary one of them until a difference is noticed (“just noticeable difference”/JND).
    1. If these colors aren’t touching but are separated a bit, the ability to differentiate possibly millions of colors goes down to thousands
  2. Systems of describing colors fall into two main categories:
    1. Those for describing the physical characteristics of the color
    2. Those describing the psychometric/perceptual color sensations
  3. Many aspects of psychometrics of color are tricky to measure.  Taking light blue and strong yellow, when the colors are far apart , people say the light blue is lighter, but close together they will say the strong yellow.  Are people paying attention to lightness, or whiteness?
    1. Similarly, lightness can only be defined relatively and not absolutely (although whiteness can be defined absolutely)
  4. Two main systems are Hering’s Natural Color System (based on his opponent-process model), and Munsell’s.
  5. Munsell

  6. Munsell was actually a painter, there were a few ways he did things that were incorrect
  7. Totally phenomenological
  8. Vertical axis for “Value” (lightness), and perpendicular axis of “Chroma” (color strength) and then a color wheel for hue <still not sure I really understand distinction between value and chroma, but a helpful description>
  9. “Due to the fact that the colors of maximal strength for different Hues vary both in Chroma and Value, the graphical representation becomes both irregular and skewed…”
    1. Because of this, he later left phenomenological approach and moved to psychophysics <what is the difference exactly?>
  10. Value goes from 0 to 10 (theoretically), but the ends of those ranges can’t be produced (purely reflective, absorptive) so samples used ranged from 0.5-9.5
  11. Chroma is how far from the grey axis
  12. Hue is the weirdest in his system, because of how he set it up.  He originally wanted 10 colors (to make a metric system), but that didn’t work out so he decided he would make 5 main hues.  There were lots of arbitrary decisions.  He started at a green that he felt was neither warm nor cold, and then found 4 other colors through trial and error that made neutral grey when put on a disk with this green and spun.  This yielded a red, yellow, purple, and blue
    1. Based on this, the color circle is considered to be partitioned into 5 visually equal parts <although the way it was done would have any reason to make this claim true>
  13. He then ended up with the 10 colors he wanted by inserting additional hues midway between the 5 he started with, and then 10 more times each, which gave 100
    1. There is a pretty complex way of referring to color in his system
  14. After Munsell passed, technology allowed for analytical examination of his system, which turned up irregularities.  It was then revised through a tremendous undertaking.  Some seem to think the revision actually made it worse, by trying to smooth out <through distortions?> the original data, it made it less accurate
  15. The author of the chapter does not seem to like this system very much
  16. Natural Color System

  17. It was created because it was felt there were too many problems with existing systems (including Munsell’s>
  18. Munsell’s was stimulus based, but this is a theoretical/cognitive system <guess I’ll find out what that means more specifically>
  19. It was based on Hering’s approach – was based on 6 elemental colors (RGBYWBk)
  20. Because a color can’t resemble more than 4 elementary colors, so the unit of measurement is percent resemblance to the elementary color X
  21. When put in a color wheel, opposing colors are opposite.  The system wasn’t designed to fit in a wheel but it happens to do so nicely and is done this way because of convention
  22. Colors of a given hue in this system rendered in a equilateral triangle.  Corners are (elementary) white, (elementary) black, and max chromaticness.  “chromaticness” is similar to Munsell’s chroma but Munsell’s is open-ended, whereas chromaticness has a closed range 0-100
  23. NCS color space is then a wheel where a triangle goes around, so its a sort of diamond, or top-shape
  24. <Conceptually, I have a much easier time understanding this system than Munsell’s>
  25. People will usually place the same color in the same place in NCS color space with about 3-5% disagreement between them
  26. The notation is also simpler, 3 digits of blackness, chromaticness, and hue, although this is actually overdetermined, and you can go with just 2 of the 3 and infer the 3rd since everything is on 0-100 scale
  27. Comparison of Munsell and NCS

  28. There is an NCS atlas that attempts to document the NCS color diamond <my word> but the distinction between this and the Munsell atlas, is that in the case with Munsell, that atlas defines the colors itself (and is only valid in the lighting and viewing conditions specified for examining the atlas).  In NCS its the 3 digit description of the color that defines it
    1. “The Munsell system is thus dependent on its atlas, but NCS is not.”
  29. The 3 dimensions in Munsell and NCS do not mean the same thing, and there is not necessarily a straightforward way to go between them because of fundamental differences in what the variables are taken to mean (Munsell’s discriminative vs NCS’ descriptive)
  30. The color wheels used by the two are also not the same, with Munsell’s blue different from “unique” <elemental?> blue
  31. <rest of chapter goes on to things like color-word associations so I’m skipping that>
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