by Cousin Ricky » Wed Oct 02, 2013 4:41 pm
Ann wrote:I'm going to offer a nitpick, however, and say that this picturre does not, in fact, show us all the colors of the Sun. The color violet is missing. The violet color can clearly be seen in
this picture of a rainbow, so presumably violet is a real color of the Sun. Another color which is there in today's APOD, but which gets rather short shrift, is orange.
In addition to differences between monitors and monitor calibration mentioned by others, a fundamental problem is that all colors cannot be accurately represented on a color monitor. This is especially true of pure spectral colors.
Your monitor reconstructs colors using three primary colors to reproduce the effect on your retinas; however, not all colors can be reproduced exactly. The problem is well illustrated in this
gamut diagram. There are various
algorithms for finding the “nearest” color within a gamut, but the situation is analogous to projecting a round globe onto a flat map: something has to get distorted.
This is less of a problem with photographs (such as your rainbow) because typical scenes do not have saturated hues.
The orange on Mr. Sharp’s spectrum looks fine to me. I’d say that the cyan region looks a little too green, but I know of at least one algorithm that produces this effect. Other algorithms produce a bluer hue, but at the expense of brilliance. (You’ll notice that towards the blue end, the cyan looks rather muddy. This is unavoidable on an sRGB monitor, which yours probably is unless you know otherwise.)
Ann wrote:The colors of the Sun, judging from today's APOD, are sharply red, green and blue, with a few "intermediate colors". I would guess that the reason for this three-color aspect of the Sun is that it was photographed through red, green and blue filters.
I suspect the reason is Mr. Sharp’s gamut mapping algorithm, but one would have to ask him to be sure.
[quote="Ann"]I'm going to offer a nitpick, however, and say that this picturre does not, in fact, show us all the colors of the Sun. The color violet is missing. The violet color can clearly be seen in [url=http://s0.geograph.org.uk/photos/96/24/962472_a5c85c56.jpg]this picture of a rainbow[/url], so presumably violet is a real color of the Sun. Another color which is there in today's APOD, but which gets rather short shrift, is orange.[/quote]
In addition to differences between monitors and monitor calibration mentioned by others, a fundamental problem is that all colors cannot be accurately represented on a color monitor. This is especially true of pure spectral colors.
Your monitor reconstructs colors using three primary colors to reproduce the effect on your retinas; however, not all colors can be reproduced exactly. The problem is well illustrated in this [url=http://en.wikipedia.org/wiki/File:Cie_Chart_with_sRGB_gamut_by_spigget.png]gamut diagram[/url]. There are various [url=http://en.wikipedia.org/wiki/Gamut_mapping#Gamut_mapping]algorithms[/url] for finding the “nearest” color within a gamut, but the situation is analogous to projecting a round globe onto a flat map: something has to get distorted.
This is less of a problem with photographs (such as your rainbow) because typical scenes do not have saturated hues.
The orange on Mr. Sharp’s spectrum looks fine to me. I’d say that the cyan region looks a little too green, but I know of at least one algorithm that produces this effect. Other algorithms produce a bluer hue, but at the expense of brilliance. (You’ll notice that towards the blue end, the cyan looks rather muddy. This is unavoidable on an sRGB monitor, which yours probably is unless you know otherwise.)
[quote="Ann"]The colors of the Sun, judging from today's APOD, are sharply red, green and blue, with a few "intermediate colors". I would guess that the reason for this three-color aspect of the Sun is that it was photographed through red, green and blue filters.[/quote]
I suspect the reason is Mr. Sharp’s gamut mapping algorithm, but one would have to ask him to be sure.