Adobe 13101332 User Guide - Page 99
Number of colors, Color inclusion and transparency, Dithering, Previous, Forced, Transparency, Matte
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Adobe Photoshop Help Using Help | Contents | Index Working with Color Back 99 Previous Uses the custom palette from the previous conversion, making it easy to convert several images with the same custom palette. Number of colors For the Uniform, Perceptual, Selective, or Adaptive palette, you can specify the exact number of colors to be displayed (up to 256) by entering a value for Colors.The Colors text box controls only how the indexed color table is created. Adobe Photoshop still treats the image as an 8-bit, 256-color image. Color inclusion and transparency To specify colors to be included in the indexed color table or to specify transparency in the image, choose from the following options: Forced Provides options to force the inclusion of certain colors in the color table. Black and White adds a pure black and a pure white to the color table; Primaries adds red, green, blue, cyan, magenta, yellow, black, and white; Web adds the 216 web-safe colors; and Custom lets you define custom colors to add. Transparency Specifies whether to preserve transparent areas of the image during conversion. Selecting this option adds a special index entry in the color table for transparent colors. Deselecting this option fills transparent areas with the matte color, or with white if no matte color is chosen. Matte Specifies the background color used to fill anti-aliased edges that lie adjacent to transparent areas of the image. With Transparency selected, the matte is applied to edge areas to help blend the edges with a Web background of the same color. With Transparency deselected, the matte is applied to transparent areas. Choosing None for the matte creates hard-edged transparency if Transparency is selected; otherwise, all transparent areas are filled with 100% white. Dithering Unless you're using the Exact color table option, the color table may not contain all the colors used in the image. To simulate colors not in the color table, you can dither the colors. Dithering mixes the pixels of the available colors to simulate the missing colors. Choose a dither option from the menu, and enter a value for the 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. Using Help | Contents | Index Back 99