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The paletted color mode, also called indexed color mode, is frequently used for GIF images on the web. When you convert a complex 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. As a result, the paletted image contains less data than the original, and it has a smaller file size. Paletted color mode is an 8-bit mode that stores and displays images by using up to 256 colors.
Choosing, editing, and saving a color palette
When you change an image to the paletted color mode, you use a predefined or a custom color palette and then edit the palette by replacing individual colors. If you choose the Optimized color palette, you can also edit the palette by specifying a range sensitivity color. The color palette you use to convert the image is called the processed color palette, and it can be saved for use with other images.
For more information about creating custom color palettes, see Working with color.
Dithering
Paletted images can only contain up to 256 different colors. If the original image contains many colors, you can use dithering to create the illusion of seeing more than 256 colors. Dithering creates additional colors and shades from an existing palette by interspersing pixels of different colors. The relationship of one colored pixel to another creates an optical mix, so you perceive additional colors.
Dithering can be done by distributing colors either regularly or randomly. Ordered dithering approximates color blends by using regular dot patterns; as a result, solid colors are emphasized and edges appear harder. Error diffusion scatters pixels randomly, making edges and colors softer. Jarvis, Stucki and Floyd-Steinberg are methods of error diffusion.
If your image contains only a few colors and simple shapes, you do not need to use dithering.
Setting the color range for a custom color palette
When you change an image to the paletted color mode using the Optimized palette, you can choose a seed color, or base color, and a range sensitivity for the seed color. The seed color, and similar 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 seed color reduces the number of colors that fall outside the range sensitivity.
Saving conversion options
After you choose a color palette and set the dithering and range sensitivity for the changing of an image to the paletted color mode, you can save the selected options as a conversion preset that you can use with other images. You can add and remove as many conversion presets as you want. You can also remove the presets you have added.
Converting multiple images to the paletted color mode
You can change multiple images to the paletted color mode simultaneously. Before you perform a batch conversion, you must open the images in Corel PHOTO-PAINT. All images that you include in the batch are changed using the color palette and conversion options you specify.
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Click Image  Convert to paletted (8-bit). |
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Uniform — provides a range of 256 colors with equal parts of red, green, and blue |
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Adaptive — provides colors original to the image, and preserves the individual colors (the entire color spectrum) in the image |
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Optimized — creates a color palette based on the highest percentage of colors in the image. You can also select a range sensitivity color for the color palette. |
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Black Body — contains colors that are based on temperature. For example, black may represent cold temperatures, while red, orange, yellow, and white may represent hot temperatures. |
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Grayscale — provides 256 shades of gray, ranging from black (0) to white (255) |
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Websafe — provides a palette of 216 colors that are common to web browsers |
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Move the Dither intensity slider to adjust the amount of dithering. |
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Click Add preset  , and type a name in the Save preset box.
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Click the Processed palette tab, and click Edit. In the Color table dialog box, edit the color palette.
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Click the Processed palette tab, and click Save. Choose the folder where you want to save the processed color palette, and type a filename.
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The Ordered dithering option is applied more quickly than are the error diffusion options Jarvis, Stucki, and Floyd-Steinberg; however, it is less accurate.
You can choose a custom color palette by clicking the Options tab, clicking Open, locating the color palette file you want, and double-clicking the filename.
You can load preset conversion options by choosing a preset from the Presets list box on the Options tab.
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Click Image Convert to paletted (8-bit). |
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Choose Optimized from the Palette list box. |
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Enable the Color range sensitivity to check box. |
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Click the Eyedropper tool  , and click a color in the image. |
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Click the Range sensitivity tab, and specify the settings you want. |
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Click Image Convert to paletted (8-bit). |
You can preview an image by choosing it from the Preview image list box and clicking Preview.
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