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 custom color palettes.”
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.
The table below outlines available palette types.
To change an image to the paletted color mode
If you want to save the conversion settings as a preset, click the Add preset button, and type a name in the Save preset box.
You can choose a custom color palette by clicking Open, locating the color palette file you want, and double-clicking the filename.
To create a custom processed color palette
To change a bitmap by setting range sensitivity