== colors in chromaticity diagrams == 

 Hi PAR, I’ve been trying to draw some chromaticity diagrams, to upload in SVG format, and thought you might have some thoughts about it. I’m somewhat skeptical of coloring the chromaticities outside the sRGB gamut, since it is impossible to properly represent them. Among other things, it seems sorta odd to show colors near the spectral locus at the same luminance as colors near the middle of the gamut – to be at a similar luminance, they’d have to emit quite a bit of light at their specific wavelengths – near the red/blue corners, that would have to be quite a lot indeed, given the low human sensitivity to those wavelengths. Next, I’m not a fan of the bright “star” (your word) artifact near white. It’s not clear to me that showing the maximum available Y for each (x, y) is a good strategy; in trying a few mappings from (x, y) to Y, I think I’ve decided that the one which works best is to take a plane in XYZ space through the XYZ values for the three sRGB primaries. This doesn’t result in a completely uniform luminance, but it is a pretty smooth surface in xyY space, and goes through as-bright-as-possible (1, 0, 0), (0, 1, 0), (0, 0, 1) points in RGB at the three corners. I think I’d just as soon *not* fill in the portion of the “horseshoe” outside the sRGB gamut triangle, instead explaining in captions wherever the image is used that those colors should be “like the ones shown but more colorful” &c.; Finally, I think it often it makes sense to use the 1976 (u′, v′) diagram rather than the 1931 (x, y) diagram, for instance in diagrams comparing various RGB gamuts, or diagrams indicating the chromaticity of various white points. I’ll try to upload the diagrams as I’ve been working on them so far and link them here, shortly. –