RGB Formulas

All color models use mathematical designations to represent the different variations of color. RGB uses 256 (0 to 255) steps for each color. (That number should look familiar to anyone who knows the basics of computers, because 256 points of data is the amount of information inherent in 8-bit data. Since RGB has 8 bits of data for each of the three primary colors, it is a 24-bit color model, because 3 x 8 equals 24.)

Therefore, red can have a value of 0 to 255, as can green and blue. So, white is written as R255, G255, B255, and black is R0, G0, B0. Every possible color within the RGB color space can be described in this manner. For example, a certain shade of orange is R236, B149, B52.

While you won't need to know about these numbers while shooting, they will be useful to you when editing your photographs, especially should you need to match a specific color, such as a corporate logo. Many image-editing programs, such as Corel PhotoPaint and Photoshop Elements 2.0, have tools for determining the RGB numerical value of any portion of the image.


All digital cameras that we know about use sRGB as their default working color space. Hewlett-Packard and Microsoft developed this color model, which includes all the colors that can be displayed on a typical computer monitor. While it is great for images that will spend their entire existence only in computers or on the Web, it has a limited gamut. In other words, it doesn't encompass as many colors as other color models.

Some of the more advanced digital cameras can switch from sRGB to Adobe RGB. Introduced in 1998 for Photoshop 5.0, Adobe RGB was originally designated Adobe RGB 1998, a name that is rarely used today. 5.0 was the first Photoshop to have color management (see Chapter 20), and Adobe RGB was only one of several color models offered in a system that was initially, at best, a hodge-podge based on guesstimates of what should work. According to Adobe, as graphics pros, prepress experts, and photographers explored the new tools, they found that Adobe RGB was the one color model that worked best for prepress and photography workflows.

Adobe RGB includes a larger range (gamut) of colors than sRGB, especially in the blues and cyans, which is what makes it more appropriate for print output.

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