Optimizing colors in GIF and PNG-8 images

To select a color reduction algorithm:

Choose an option from the Color Reduction Algorithm pop-up menu (below the file format menu in the Optimize panel/palette):

Perceptual Creates a custom color table by giving priority to colors for 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 color table usually produces images with the greatest color integrity. Selective is the default option.

Adaptive Creates a custom color table by sampling colors from the spectrum appearing most commonly in the image. For example, an image with only the colors green and blue produces a color table made primarily of greens and blues. Most images concentrate colors in particular areas of the spectrum.

Web Uses the standard 216-color color table common to the Windows and Mac OS 8-bit (256-color) palettes. This option ensures that no browser dither is applied to colors when the image is displayed using 8-bit color. (This palette is also called the Web-safe palette.)

If your image has fewer colors than the total number specified in the color palette, unused colors are removed.

Using the Web palette can create larger files, and is recommended only when avoiding browser dither is a high priority.

Custom Preserves the current color table as a fixed palette that does not update with changes to the image.

Mac OS Uses the Mac OS system’s default 8-bit (256-color) color table, which is based on a uniform sampling of RGB colors. If your image has fewer colors than the total number specified in the color palette, unused colors are removed.

Windows Uses the Windows system’s default 8-bit (256-color) color table, which is based on a uniform sampling of RGB colors. If your image has fewer colors than the total number specified in the color palette, unused colors are removed.

Other color tables appear in the menu if you have saved them previously. (See “Loading and saving color tables” on page 437.)

You can use an alpha channel to influence the generation of color tables. (See “Using masks to modify color reduction” on page 430.)

To regenerate a color table (ImageReady):

Choose Rebuild Color Table from the Color Table palette menu. Use this command to generate a new color table when the Auto Regenerate option is off. (See “Controlling optimization (ImageReady)” on page 426.)

Changing the display of the color table

You can sort colors in the color table by hue, luminance, or popularity, making it easier to see an image’s color range and locate particular colors. In ImageReady, you can also change the size of the color swatches in the color table.

To sort a color table:

Choose a sorting order from the Color Table palette menu:

• Unsorted. Restores the original sorting order.

To add black or white to the color table for an image:

1Choose black or white as the foreground color. (See “Choosing foreground and background colors” on page 257.)

2Add the color to the color table. (See “Adding new colors to the color table” on page 433.)

Selecting colors

You select colors directly in the optimized image or in the color table. In ImageReady, you can select a color from another application, such as a Web page displayed in a browser.

To select a color from the optimized image:

1Select the eyedropper tool in the Save for Web dialog box (Photoshop) or the toolbox (ImageReady).

2Click a color in the image. A white border appears around that color in the color table. Shift-click to select additional colors.

To select a color from another application (ImageReady):

(ImageReady) Select the eyedropper tool, click in the image, hold the mouse down, and drag anywhere on the desktop. You can use this option to select a color displayed in another application, such as a color in a Web page displayed in a browser.

To select a color directly in the color table:

Click the color in the Color Table palette.

To select a contiguous group of colors, press Shift and click another color. All colors in the rows between the first and second selected colors are selected.

To select a discontiguous group of colors, press Ctrl (Windows) or Command (Mac OS) and click each color that you want to select.

To select colors based on a selection in the image (ImageReady):

1Make a selection in the image using the selection tools or the Select menu commands.

2Choose Select All From Selection from the Color Table palette menu.

To select all colors:

Choose Select All Colors from the Color Table palette menu.

To select all Web-safe colors:

Choose Select All Web Safe Colors from the Color Table palette menu.

To select all non-Web-safe colors:

Choose Select All Non-Web Safe Colors from the Color Table palette menu.

To view selected colors in an image (ImageReady):

Select the optimized image. Then click and hold a selected color in the Color Table palette to temporarily invert the color in the optimized image, enabling you to see which areas of the image contain the color.

To view a contiguous group of colors, press Shift and click and hold another color. All colors in the rows between the first and second selected colors are inverted.