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Tuesday, January 16, 2007

Color Spaces & Printer Profiles Revealed

Crayon color choices have some important similarities to how color spaces are defined and used

Labels: How ToPrinting
While it's correct to say that Adobe RGB is a wider color space, that statement can be misleading. Some people misunderstand it to mean that Adobe RGB offers more colors, but that's not the case. Adobe RGB has a wider gamut but offers exactly the same number of colors as sRGB. That's an unbendable law of physics. All 8-bit RGB images, which include both Adobe RGB and sRGB, have a bit depth of 24 (that is, 8 bits multiplied by the number of channels, which in this case is three—Red, Green and Blue). Similarly, all 8-bit RGB images have 256 possible color values per channel, and that equates to 16.7 million colors (256 x 256 x 256). Then what's the difference?

Back to the Crayola Factory. Imagine 1,000 crayons standing upright, shoulder-to-shoulder. If you were to take a lasso and surround 64 of the adjacent colors that are more or less in the middle of the array, you'd be able to assemble a box of crayons similar to what you used at school. This represents sRGB. But if you were to selectively skip over some of the colors—in fact, remove them from the assortment entirely—and instead include some of the brighter greens and blues, for example, you could put together a very different set. The lasso you used in the first example won't fit around this new set. This new selection of crayons isn't standing shoulder-to-shoulder like the first group—there are a few gaps and the pieces are more spread out. You need a bigger lasso because some of the crayons are farther away from the center.

Adobe RGB has the same number of colors as sRGB, but some of the colors are different. The gamut is wider, and we can say that the color space is larger in the same way that we needed a bigger lasso to harness the crayons in the example above. This explains why Adobe RGB occupies more area on color space diagrams that compare it to sRGB. The same number of colors—but they're more widely dispersed from the central area.




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