Customizing indexed color tables (Photoshop)

Customizing indexed color tables (Photoshop)

The Color Table command lets you make changes to the color table of an indexed-color image. These customization features are particularly useful with pseudocolor images- images displaying variations in gray levels with color rather than shades of gray, often used in scientific and medical applications. However, customizing the color table can also produce special effects with indexed-color images that have a limited number of colors. Note: To shift colors simply in a pseudocolor image, choose Image > Adjust, and use the color adjustment commands in the submenu. For a summary description of these commands, see "Basic steps for correcting images" on section 129.

Using the color table to edit colors and assign transparency

You can edit colors in the color table to produce special effects, or assign transparency in the image to a single color in the table.

To edit colors in the color table:

1 Open the indexed-color image.

2 Choose Image > Mode > Color Table.

3 Click or drag in the table to choose the color or range of colors you want to change.

4 Choose a color, as explained in "Using the Adobe Color Picker" on section 261, and click OK.

If you are changing a range of colors, Photoshop creates a gradient in the color table between the starting and ending colors. The first color you choose in the Color Picker is the beginning color for the range. When you click OK, the Color Picker reappears so that you can choose the last color in the range.

The colors you selected in the Color Picker are placed in the range you selected in the

Color Table dialog box.

5 Click OK in the Color Table dialog box to apply the new colors to the indexed-color image.

To assign transparency to a single color:

1 Choose Image > Mode > Color Table.

2 Select the eyedropper, and click the desired color in the table or in the image. The sampled color is replaced with transparency in the image.

Using predefined color tables

Your indexed color table can be modeled after predefined color tables, which you select from the Table menu in the Color Table dialog box.

Custom Creates a palette you specify.

Black Body Displays a palette based on the different colors a blackbody radiator emits as it is heated-from black to red, orange, yellow, and white.

Grayscale Displays a palette based on 256 levels of gray-from black to white. Spectrum Displays a palette based on the colors produced as white light passes through a prism- from violet, blue, and green to yellow, orange, and red.

System (Mac OS) Displays the standard Mac OS 256-color system palette. System (Windows) Displays the standard Windows 256-color system palette. Saving and loading color tables

You use the Save and Load buttons in the Color Table dialog box to save your indexed color tables for use with other Adobe Photoshop images. Once you load a color table into an image, the colors in the image change to reflect the color positions they reference in the new color table.

Note: You can also load saved color tables into the Swatches palette. (See the procedure to save and reuse custom swatch sets in "Using the Swatches palette" on section 260.)