Adobe Photoshop CS2 On Demand [Electronic resources] نسخه متنی

Understanding the Indexed Color Mode

The indexed color mode gives you two advantages. You can create images as small as grayscale (8-bit pixels), and you get color instead of shades of gray. Its small file size, and its ability to generate color make is a winning color mode for images displayed on Web pages, as well as graphics used in computer-generated presentations. Its one drawback is the number of colors generated, indexed images generate a maximum of 256 colors (the same as the steps of gray in a grayscale image). The good news is you get to choose the colors. When you convert an image into the indexed color mode, Photoshop creates a color lookup table (CLUT) to store the images color information. When a color in the image cannot be found in the lookup table, Photoshop substitutes the closest available color.

Convert an Image to Indexed Color

Open an image.

Click the

Image menu, point to

Mode , and then click

Indexed Color .

Select from the following Indexed Color Mode options:

• 
  

  Palette.
  Click the list arrow to choose from the available color palettes, or click Custom and create your own palette.

• 
  

  Colors.
  Select the number of colors for the lookup table (9 to 256).

• 
  

  Forced.
  Force the lookup table to hold specific colors. 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 allows you to specify your own colors.

• 
  

  Transparency.
  Select the check box to preserve transparent areas of the image (if there are no transparent areas, this option is disabled).

Select from the following options:

• 
  

  Matte.
  Click the list arrow to fill transparent areas of the original image with a specific color.

• 
  

  Dither.
  Click the list arrow, and then select a pixel-mixing (dither) scheme. Dithering helps transitional areas of the image (shadows, light to dark) appear more natural.

• 
  

  Amount.
  If the Dither option is selected, the Amount instructs Photoshop how much color information to use in the dithering process (0 to 100).

• 
  

  Preserve Exact Colors.
  Select the check box to hold exact color measurements in the lookup table.

Click

OK .

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