Talk:Color constancy

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The demonstration figures need work. The first is a lightness illusion -- not color constancy The second is unclear -- for color constancy, you need to have a different RGB color in the image appearing to be the same perceptual color to the viewer. In this case, the RGB values are different, but the colors also look different.

From the article:

early morning daylight, whose main component is bluish, and also in the late afternoon light, when the main component is reddish.

You sure about that? The color of sunlight on Earth's surface depends on the amount of atmosphere it's passing through, ie the angle of elevation of the Sun above the horizon. Early morning and late afternoon should look the same.

Perhaps the author of that passage doesn't get up early enough to be aware of the sunrise phenomenon. :) Or else is referring to pre-dawn light, which will lack direct sunlight and be deflected (bluish) light from the atmosphere... same as dusk. --Brion

"The effect was discovered in 1971 by Edwin Land."

(The inventor of the Polaroid ?)

I seriously wonder if he discovered it. He may have theorized it. But every photographer knew it before. If you take photo in artificial light with a daylight slide film the picture is very orange.

Ericd 01:17 Apr 7, 2003 (UTC)

At second thought this has a lot of connection with photography aren't retinex algorithms an automatic white balance algorithms ? Ericd 01:22 Apr 7, 2003 (UTC)

Is the caption of the figure with the guy holding the cards accurate? Isn't the whole point of the article that you can add a shade (of pink, say) to an image and have it look the same even though the actual intensity of the pinks might be different? Maybe I'm just confused about the caption? 131.243.77.221 (talk) 01:12, 18 November 2007 (UTC)

[edit] Is “Discounted” a special term?

I am surprised by the use of the word “discounted” in the phrase: “This illumination is then discounted” Is it a technical term? Can it be defined or “glossed” or better explained here? Would a word such as “normalized” be better? Would it be better to say that “the spectral characteristics of the illumination are estimated and this estimate is used to interpret the colors of the reflected light”? --Lbeaumont 13:55, 7 November 2007 (UTC)

"Discounted", a term that goes back to Helmholtz in the 19th century, is the most justifiable and model-independent term of which I am aware. The illumination is "discounted" if a scene looks the same under one illumination as under another. It is a matter of (I think misguided) modern dogma to <define> color constancy as estimating the illuminant spectrum prior to compensating it. Surely retinex ratios don't do this, and neither do many other color-constancy algorithms including some that parameterize reflectance but not illuminant spectra. Michael H. Brill12.26.40.88 (talk) 16:35, 4 January 2008 (UTC)