Another important factor in any graphic is the color used in it. The right colors can make an image sing; the wrong colors turn that song into a dirge. To produce colors that enhance your images, you need to have a good understanding of how your Mac works with color.
Your Mac uses two basic techniques to work with color. With one, your Mac specifies a color's coordinates in a color space. With the other, your Mac specifies the color's position in a fixed palette of colors.
A color space is simply a system that uses a set of numbers to represent the gamut of possible colors. Many Mac applications use the Red Green Blue (RGB) color space, which breaks down colors into their red, green, and blue components. Another common color space is HSB, which breaks down color into Hue, Saturation, and Brightness components. Most printers use the Cyan Magenta Yellow blacK, or CMYK, color space.
The "amount" of each component (red, blue, and green, or hue, saturation, and brightness) in a color is indicated by a number that represents how much of that component is in a particular color. The number for each component can be in the range from zero to 255.
For example, in the RGB color space, "pure" red is represented as (255,0,0), as in the following:
Red = 255
Blue = 0
Green = 0
Using coordinates to specify the color of each pixel in an image enables you to choose each pixel's color from a set of more than 16 million possible colors. This system, sometimes called "true color" or "full color," yields the most natural-looking displays on a monitor, and is the color system used in all serious file formats for color printing.
The extreme resource requirements of color spaces led to the development of color palettes. They solve the resource problem by using a system of abbreviations to store each pixel's color. For example, suppose an image has a palette of four colors, such as the following:
color 0 = (0,0,0) (white)
color 1 = (255,255,255) (black)
color 2 = (255,0,0) (red)
color 3 = (0,0,255) (blue)
Rather than having to store three pieces of information for the color of each pixel, your Mac has to store only one piece of data?the number of the color on the palette. This requires fewer resources than storing the numbers of the three components.
The number of colors on a palette is called its bit depth?bit depth refers to how many bits of data are required to store the color for each pixel in an image. The common bit depths and resulting number of colors are shown in Table 15.2.
|Bit Depth||Number of Colors|
The number of colors in a palette is determined by raising 2 to the number of bits required to store the data needed to define that amount of color. For example, 8-bit depth results in 256 colors (2 raised to the eighth power).
Some graphic formats have inherent color limitations. For example, the GIF format is limited to a color depth of 256 colors (which makes it unsuitable for most photographs).
To learn more about image file formats, see "Mac OS X to the Max: Image File Formats," p. 455.
Windows PCs also use color palettes similar to the Mac's. However, the same colors will appear darker on a Windows machine than they do on a Mac. If you are designing an image that will be viewed on Windows machines also, try to make the colors a bit lighter than you might choose for images used only on the Mac.
For both resolution and color depth, if you are developing an image that will be widely distributed (such as on a Web page), you will get a better result if you design your image for the capabilities of the lower end of your target market. For example, if you create an image at the 16-bit color depth, but the bulk of your audience can use only 8-bit color, some of your work will be lost because the viewer's computer will have to trim the number of colors down. Plus, higher bit-depth images are larger and require more time to download and to display after they are loaded on a machine.
It is always a good idea to take a look at any image you create in various resolutions and color depths to make sure that it looks okay in as many situations as possible. You should also view it on multiple platforms as well.