Color perception

Jim McKenney
Fri, 23 Jan 2004 16:36:30 PST

Your first paragraph made me think of harmonics and difference tones in
music. BTW, what's the CIE standard color space?

Your second paragraph reminded me of the ultimate test for color film in
the old days: Ipomoea Heavenly Blue. 

Jim McKenney
in a colorless but neverthless blue place

t 02:59 PM 1/23/2004 -0800, you wrote:
>--Lee Poulsen
>Pasadena area, California, USDA Zone 9-10On Jan 23, 2004, at 2:24 PM, 
> wrote:
>> Printers wrestle with this metamerism problem all the time.  Two 
>> objects made
>> from two different pigments may look the same under one light source, 
>> but
>> different under another light source.  Happens all the time to interior
>> decorators.
>And in a similar vein, from what I've read, humans will perceive two 
>colors as being the same if they both lie at the same coordinates in 
>the CIE standard color space, no matter how the color is produced. If a 
>human sees a source of light consisting of two different frequencies in 
>the visible light spectrum, it will appear as a single color that lies 
>at the midpoint between the two frequencies locations in the standard 
>color space. However, this point can often correspond to a source of 
>light consisting of a single frequency. Either one of these sources of 
>light will appear the same color to most humans, even though one is a 
>spectrally "pure" frequency corresponding to that color and the other 
>is really two other colors that have mixed to produce that color.
>Why is this important? I've read that if you are trying to attract 
>flies to a bright yellow colored object (like sticky fly traps), you 
>have to use spectrally pure yellow paper or whatever. If the color of 
>the object that appears bright yellow to us really consists of two or 
>more pigments whose mixture appears bright yellow to us, the fly eye is 
>different and they don't see it as yellow at all. This is also why some 
>kinds of blue objects appear different colored in photographs than 
>other blue objects like flowers for example, making blue flowers very 
>difficult to render correctly to our perception. The photographic 
>chemicals react differently to spectral reds and spectral blues than 
>our eyes do making the flower often look wrong, even though to us when 
>we look at it directly, it looks like it's "pure" blue.
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