Palette types for indexed-color images

A number of palette types are available for converting an image to indexed color.

Exact

Creates a palette using the exact colors that appear in the RGB image--an option available only if the image uses 256 or fewer colors. Because the image's palette contains all of the colors in the image, there is no dithering.

System (Mac OS)

Uses the Mac OS default 8-bit palette, which is based on a uniform sampling of RGB colors.

System (Windows)

Uses the Windows system's default 8-bit palette, which is based on a uniform sampling of RGB colors.

Web

Uses the 216 colors that Web browsers, regardless of platform, use to display images on a monitor limited to 256 colors. This palette is a subset of the Mac OS 8-bit palette. Use this option to avoid browser dither when viewing images on a monitor display limited to 256 colors.

Uniform

Creates a palette by uniformly sampling colors from the RGB color cube. For example, if Photoshop Elements takes 6 evenly spaced color levels each of red, green, and blue, the combination produces a uniform palette of 216 colors (6 cubed = 6 x 6 x 6 = 216). The total number of colors displayed in an image corresponds to the nearest perfect cube (8, 27, 64, 125, or 216)--that is, less than the value in the Colors text box.

Perceptual

Creates a custom palette by giving priority to colors to which the human eye has greater sensitivity.

Selective

Creates a color table similar to the Perceptual color table, but favoring broad areas of color and the preservation of Web colors. This option usually produces images with the greatest color integrity.

Adaptive

Creates a palette by sampling the colors from the spectrum appearing most often in the image. For example, an RGB image with only the colors green and blue produces a palette made primarily of greens and blues. Most images concentrate colors in particular areas of the spectrum. To control a palette more precisely, first select a part of the image that contains the colors you want to emphasize. Photoshop Elements weights the conversion toward these colors.

Custom

Creates a custom palette by using the Color Table dialog box. Either edit the color table and save it for later use, or click Load to load a previously created color table. (See Customizing indexed color tables.) This option also displays the current adaptive palette, which is useful for previewing the colors most often used in the image.

Previous

Uses the custom palette from the previous conversion, making it easy to convert several images with the same custom palette.