Other Palettes 305Web PaletteOther PalettesWeb Design in a Nutshell, eMatter EditionOther Palettes
All 8-bit Indexed Color images (such as GIF or PNG-8) use a palette of colors to
define the colors in the image. The Web Palette is just one of infinite palette possi-
bilities. However, there are several standard palettes you can choose from within
popular graphics programs. This section defines the common palette choices that
will be referred to throughout this chapter.
Exact
If the image contains fewer than 256 colors, choosing the Exact palette option
makes a palette out of the actual colors that are found in the image.
Adaptive
This is a custom palette generated using the most commonly used pixel colors
in the image. Less commonly used colors are approximated by the most
commonly used colors. It allows for color-depth reduction while preserving
the original character of the image. Because the number of colors is being
reduced, some dithering and color-shifing will occur.
System (Mac/Windows)
Choosing either system palette will convert the image to the palette of 256
colors as defined by each operating system.
Uniform
This palette contains an evenly stepped sampling of colors from the RGB
spectrum.
Custom
This allows you to load in a palette that was previously saved and apply it to
the current image.
Perceptual (Adobe ImageReady only)
This creates a custom palette by giving priority to colors for which the human
eye has greater sensitivity. Unlike Adaptive, it is based on algorithms, not just
a pixel count. It generally results in images with better color integrity than
adaptive palette images.
WebSnap Adaptive (Macromedia Fireworks only)
An adaptive palette in which colors that are near in value to Web Palette
colors are converted to the closest Web Palette color.
Table 17-1: Equivalent Values of Web Palette Shades
Decimal Hexadecimal Percentage
(darkest) 000 0%
51 33 20%
102 66 40%
153 99 60%
204 CC 80%
(lightest) 255 FF 100%