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Rogo, you made this statement:
[IMG]http://www.**************.com/images/misc/quote_icon.png[/IMG] Originally Posted by rogo [IMG]http://www.**************.com/images/buttons/viewpost-right.png[/IMG]
If you overlap a red flashlight and a green flashlight and compare that to a yellow flashlight, you will see them as identical. Your brain will too.
Absolutely. You and I both agree and have both stipulated this. Where we differ is that apparently your definition of yellow light is "light that looks yellow", whereas my definition is "light that is composed of photons from a particular range of frequencies which we call the yellow part of the visible spectrum."
But I don't think it's consistent for you to use a definition of color that is based on the human physiological perception of color and then say that the primary colors are based on some property that's inherent to light. The three primary colors together produce white because, as you say, they stimulate the human eye's cones in the same manner that white light does. But if we had a different number of cones we would have to use different primaries to achieve that same identical stimulus and appear the same as a continuous spectrum.
Your quote from physicsclassroom seems needlessly pedantic to me. Of course it's true that "light is technically not colored at all. It has a wavelength." In fact "technically" it isn't light at all, it's just part of the electromagnetic spectrum. We call it light because it's that part of the spectrum that we can see. Likewise, there's a particular part of the visible spectrum that we call yellow. We do that because it stimulates both our red and green cones and we perceive it as yellow. So while it is true that there are combinations of other frequencies of light that stimulate those cones in the same way and which we also perceive as yellow, that combined light still in reality is not in the frequency range that has been given the name yellow. Perception is not reality.
But let's stick to your definition of yellow and talk about the stimulus of the red and green cones. The rec.709 standard tells you how to translate the R and G numbers of the input into how much stimulus those red and green cones are supposed to receive in order for us to perceive the intended shade of yellow.
In a non-quattron TV, that translates directly into a luminance for the red and green pixels. But in a quattron there are two sources of stimulus for those red and green cones. There are the red and green sub-pixels and there is the sub-pixel that emits actual yellow light which is going to stimulate the red and green cones simultaneously. The problem for quattron is that it has to display colors that are not simply yellow. Since as your picture shows the response curves of all the cones overlap you can't just move all the stimulus from the red and green sub-pixels over to the yellow. Some of the red is needed to go with blue to make magenta, and some of the green is needed to go with blue to make cyan. So with an input signal that has non-zero values for all of R, G, and B it isn't clear to me how you decide how much the yellow sub-pixel should contribute versus red and green.
So the computation for quattron is more complex. They have to decide how bright the red, green, and yellow sub-pixels have to be in order to achieve the stimulus called for by rec.709. It seems to me that the yellow balancing act they're forced into is almost certainly why cyan is wrong. Since green is the primary which has the largest perceived brightness, I would expect errors in the luminance of the green sub-pixel to cause the biggest effect. If they move too much of the stimulus of the green cone from the green sub-pixel to the yellow, they would be reducing frequencies that overlap with blue (since yellow light doesn't overlap with the blue cone as much as green light does) and cyan would see the biggest effect.