Changing bitmaps to the paletted color mode

The paletted color mode, also called indexed color mode, is sometimes used for images on the World Wide Web. When you convert an image to the paletted color mode, a fixed color value is assigned to each pixel. These values are stored in a compact color table, or palette, containing up to 256 colors. As a result, the paletted color mode image contains less data than a 24-bit color mode image, and it has a smaller file size. Conversion to paletted color mode works best on images that have a limited range of colors.

Choosing, editing, and saving a color palette

When you change an image to the paletted color mode, you can use a predefined palette, or you can customize a color palette by replacing individual colors.

Saving conversion settings

After you choose a color palette and set the dithering and range sensitivity for changing an image to the paletted color mode, you can save the settings as a conversion preset that you can use with other images. You can add as many conversion presets as you want.

The color palette you use is called the processed color palette. It can be saved for use with other images.

For more information about the predefined color palettes available for the paletted color mode, see Palette types. For more information about creating and opening custom color palettes, see Creating and editing custom color palettes.

Dithering

Changing images to the paletted color mode lets you use dithering to enhance color information. Dithering places pixels with specific colors or values relative to other pixels of a specific color. The relationship of one colored pixel to another creates the appearance of additional colors that do not exist in the color palette.

You can use two types of dithering: ordered dithering and error diffusion. Ordered dithering approximates color blends using fixed dot patterns; as a result, solid colors are emphasized and edges appear harder. Error diffusion scatters pixels irregularly, making edges and colors softer. Jarvis, Stucki, and Floyd-Steinberg are conversion options that provide error diffusion.

The Ordered dithering option applies more quickly than the error diffusion options (Jarvis, Stucki, and Floyd-Steinberg) but is less accurate.

Specifying a range-sensitivity color

You can change an image to the paletted color mode and specify a focus color and a range sensitivity for the focus color, so that the focus color and colors that fall within the range settings are included in the processed color palette. You can also specify how much emphasis to place on the range sensitivity. Because the palette has a maximum of 256 colors, emphasizing a focus color reduces the number of colors that fall outside the range sensitivity.

Palette types

The table below outlines available palette types.

To change an image to the paletted color mode

2 .	Click Bitmaps Mode Paletted (8-bit).

You can achieve better color fidelity by choosing the palette you want to use when you change an image to a paletted bitmap or when you export a GIF or PNG. For example, the standard color palette provides more colors than necessary for an image with a limited range of colors, but you can choose an optimized palette to ensure that color representation is accurate.

You can choose a custom color palette by clicking Open, locating the color palette file you want, and double-clicking the filename.

You can load preset conversion settings by choosing a preset from the Preset list box.

To create a custom processed color palette

2 .	Click Bitmaps Mode Paletted (8-bit).

7 .	Click the Save palette as button to save the new palette.

To change a bitmap by setting range sensitivity

2 .	Click Bitmaps Mode Paletted (8-bit).

6 .	Click the Eyedropper tool , and click a color in the image.

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