Adobe 13102498 User Guide - Page 124

PHOTOSHOP CS3 117 User Guide dither amount. A higher amount dithers more colors but may increase file size. You can choose from the following dither options: • None Does not dither colors but instead uses the color closest to the missing color. This tends to result in sharp transitions between shades of color in the image, creating a posterized effect. • Diffusion Uses an error-diffusion method that produces a less structured dither than the Pattern option. To protect colors in the image that contain entries in the color table from being dithered, select Preserve Exact Colors. This is useful for preserving fine lines and text for web images. • Pattern Uses a halftone-like square pattern to simulate any colors not in the color table. • Noise Helps to reduce seam patterns along the edges of image slices. Choose this option if you plan to slice the image for placement in an HTML table. Customize indexed color tables 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 > Adjustments, and use the color adjustment commands in the submenu. Edit colors and assign transparency with a color table 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. 1 Open the indexed-color image. 2 Choose Image > Mode > Color Table. 3 To change a single color, click the color and choose a new color in the color picker. 4 To change a range of colors, drag in the table to choose the range of colors you want to change. In the color picker, choose the first color you want in the range and click OK. When the color picker redisplays, choose the last color you want in the range and click OK. The colors you selected in the Color Picker are placed in the range you selected in the Color Table dialog box. 5 To assign transparency to a color, select the Eyedropper tool in the Color Table dialog box, and click the color in the table or in the image. The sampled color is replaced with transparency in the image. 6 Click OK in the Color Table dialog box to apply the new colors to the indexed-color image. Choose a predefined color table 1 Open the indexed-color image. 2 Do one of the following: • Choose Image > Mode > Color Table. • Choose Image > Mode > Indexed Color. In the Indexed Color dialog box, choose Custom from the Palette menu. This opens the Color Table dialog box. 3 In the Color Table dialog box, choose a predefined table from the Table menu. Custom Creates a palette you specify.