schip666! said:
You are absolutely right. I don't care about monkeys either...but it's the only data I've been able to access.
My point, which may be minor or moot, is this: to distinguish spectral-violet as a different "color" from blue we need to get some kind of additional sensory information. This could be just the declining ratios of red and green -- but that implies to me that we could "fake" a sensation of spectral violet by adding a bit of "pure" red and green to a mostly blue signal.
R,Gand B signals are not the outputs from your sensors. You need to get your terms defined properly if you want to get this straight. RGB are weightings of three standard primaries for a match with the colour you want to produce. There is loads of data showing the sensitivity of the eye receptors to the spectral colours - wiki shows some of these HML figures on that graph.
Since we can get a sensation of magenta, which is kinda like violet but not really (at least to my color memory since I haven't seen any good violets lately), by mixing only red with blue it would seem ockhams-razorish that the sensation of violet also has just a bit of red-signal in the mix. Thus my hypothesized and slightly proven-in-monkeys red-bump-in-the-blue argument.
The violet that we can actually produce with RGB signals is, indeed, inside the primary triangle and does involve red. Without some red and green, all you would get would be the primary blue (0,0,255). With equal R and B (255,0,255), you get saturated Magenta and adding some G and a bit less than equal R, you get violet(ish) colours, say (100,50 ,255).
All this is not helped by the fact that the primaries are not monochromatic, afaik, so the 'colour' of the blue primary could not actually lie exactly on the curved portion of the CIE chart - it would have to lie inside.
Looking at the Photoshop magentas pallet -- which don't seem to match a nice violet -- somewhat convinces me that there is something else going on, but I would need a good spectral-violet signal for comparison.
How many more times do I have to make this point? The Photoshop pallette consists colours that already have been synethesised with primaries. How could you expect it to have any real validity for colours outside the triangle?
Also the easily thrown number of colors distinguishable by the human eye is around 1 million, so the sensors have less than 8 bits of resolution and are probably logarithmic in response...Which is another thing that has always puzzled me: aren't "CRT" displays by nature linear, i.e., twice as much signal makes twice as much light? So how do they get matched to the eye? Are the 1 million stretched over the "extra" 15M colors in an 8+8+8 bit representation by mapping somehow?
Ah well...
The linearity is, indeed a problem and limits the exposure range of digital cameras. TV pictures and prints have a very limited contrast ratio. A contrasty scene can reveal all sorts of detail to the eye of the person there but the low level stuff is way down in the quantising noise because you are only dealing with a few bits of resolution.
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