how the eye sees color

dear all

i remember vaguely from anatomy either in high school or at the university a million years ago that the eye "sees' color differently that the three primary color camera . . . .

perhaps somebody out there could report on this


best

r

Hi Richard

I believe that current thinking is that there are three kinds of cones in the retina, each most sensitive to a different color (wavelength of light). There was a brief period when a hypothesis was floated that there were only two, but as far as I know this has been abandoned.

Regards

Steve Price

Dear folks -

What is being discussed under this rubric seems to focus primarily on how the eye operates as it sees colors.

There is a related aspect that might be seen as "why" colors are experienced as they are but without much accent on the mechanics or physics of the eye. This latter aspect has to do with the frequent claim that dyes made with synthetic dyes tend to harmonize better and that jarring discordant (wrong word, wrong arena, but you know what I mean) effects do not seem to occur much in pieces made with them.

But one of the tests we apply as we try to identify natural dyes visually is whether such harmony is achieved or whether some colors "jump out" at us. References to "hot" colors seem of this sort.

In a conversation here sometime back I quoted an article (perhaps something written by Harald Bohmer himself) in which the author said that such color harmony does occur in naturally dyed colors and that color "clashing" is rare (although look at some of the color usage in more recent DOBAG production which I often find does clash for me).

More, the reason given for the likely harmony in synthetic dyes, overlaps with the references to "impurities" in other thread in this salon. The impurities of particular interest in this article were those of the colors themselves. It was claimed that the reason that colors produced with natural dyes tend not to clash, is that they all contain shades of each other and especially of black. That one reason why some synthetic colors conflict is that they are too "pure" and do not contain aspects of one another. I don't know if this is true, but it is interesting.

This position drew opposition in this prior conversation with Yon Bard, a person who thinks carefully, checking in to suggest that there in fact may not be such a thing as "color harmony," or at least it seemed unlikely that we could demonstrate with objective data what it is we are pointing at with this expression.

Nevertheless, this claim and explanation retained some appeal for me.

Regards,

R. John Howe

The visual approach

Hi all,

There are several online resources available that cover the physiology of the eye, and in particular, sensing color. Of those I reviewed, this is my personal favorite:

http://webvision.med.utah.edu/

A good visual summary of the average human eye response to color is shown by this chart:




The summary function of all three cone responses puts the mean high sensitivity just to the left of the yellow band. Nighttime sensitivity is somewhat different and shifts to the left. Note that orange is just to the right of the yellow sensitivity peak; one reason that it, and light green, really jumps out at us when we look at a rug dominated by reds and blues (both of which have much lower sensitivity).

In addition to color sensitivity, the albedo (spectral reflectivity) of the wool/dye system also contributes to what looks garish and what doesn't. Transparent dyes rarely look as strident as pigmented or opaque coating dyes, and vegetable dyes rarely have the narrow spectral response of chemically formulated dyes. The one exception is when the underlying fiber is a clean bright white; in that case, even transparent dyes can be pretty bright; have a look at Uzbek ikat silks dyed with madder. They're almost as bright as the Saudi orange bags (I'm going to put the rest of my "orange" comments in Filibertos "Orange" thread).

Having worked on the development of graphic user interface software at one point in my life, I can testify that the general rule has always been: When you want to get their attention, use yellow on a dark background. And, it has been understood for a long time that pixel luminosity for red and blue tones must be boosted beyond those of green and yellow to achieve consistent image balance.

The SIGGRAPH (a computer graphics special interest group; for professionals) organization has a good review of eye physiology and its relationship to color & computing:

http://www.siggraph.org/education/materials/HyperGraph/color/coloreff.htm

Regards,
Chuck Wagner

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Chuck Wagner

Hi Chuck,

Interesting. From the site of your last link:
A related effect is called chromostereopsis, which is that pure colors located at the same distance from the eye appear to be at different distances, e.g. reds appear closer and blues more distant.
That’s also why blue is used very often as background on rugs, so red designs seem floating on it.
Guess green, which contains blue, works in the same way…
Regards,

Filiberto

Hi Filiberto -

An interesting thought, but one that it appears that Turkmen weavers didn't hit on much.

Does this suggest that the old Jim Allen thesis that some Turkmen rugs are actually drawn to produce three-dimensional effects needs to be revised to indicate that such effects on red-ground rugs are properly seen as cratered?



Regards,

R. John Howe