Color Space Page 2

The first reality we needed to consider is that 8 bits of color information is just barely enough. But now we have another issue to consider:

2. Not all colors are in gamut. The monitor you are looking at has red, green, and blue pixels. In an ideal world, the red pixels would stimulate only the red sensors in your eye, but not the blue or green ones, and likewise for the green and blue colors. But your eye is not perfect, and your monitor is not perfect (no offense). If you look at an image file that is a uniform fill of (255,0,0) (solid red), the green and blue sensors in your eye will be stimulated. Not as much as the red ones, but there is "crosstalk" between colors.

It gets worse. If you're looking at a print that is created by Cyan, Magenta, Yellow, and Black inks, the problem is even greater. There are all sorts of colors that your screen can display that no ink set, no matter how good, can display. Ink jet printers and offset presses often use more than just 4 colors (e.g., 8, 10, 12 or more colors) in order to minimize the problem, but the bottom line is that monitors can display colors, and your eye can see colors, that cannot be printed on a page.

In the image at right, on the left there are colors that are out of gamut. On the right, the out-of-gamut colors have been replaced with in-gamut colors.

The bottom line: (1) we need to make the best possible use of the 256 values we have each of red, green, and blue in our files, and (2) some of the colors we might use can't even be printed. For example, a very solid blue, (0,0,255) is unprintable. So is (0,0,254) and (0,0,253). Does it make sense to use up valuable data space with values that we can't use, while not having as much data space as we would like for other colors? No. That's why there are things like sRGB and Adobe 1998 color space algorithms. Read more on the next page.

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