Adobe Photoshop CS3 - Manual (Page 539)

PHOTOSHOP CS3
User Guide
532
(This palette is also called the web-safe palette.) Using the web palette can create larger files, and is recommended
only when avoiding browser dither is a high priority.
• Custom Uses a color palette that is created or modified by the user. If you open an existing GIF or PNG-8 file, it
will have a custom color palette.
Use the Color Table palette in the Save For Web & Devices dialog box to customize the color lookup table.
• Black and White, Grayscale, Mac OS, Windows Use a set palette of colors.
Dithering Method and Dither Determines the method and amount of application dithering. Dithering refers to the
method of simulating colors not available in the color display system of your computer. A higher dithering
percentage creates the appearance of more colors and more detail in an image, but can also increase the file size. For
optimal compression, use the lowest percentage of dither that provides the color detail you require. Images with
primarily solid colors may work well with no dither. Images with continuous-tone color (especially color gradients)
may require dithering to prevent color banding.
GIF image with 0% dither (left), and with 100% dither (right)
You can select one of the following dithering methods:
• Diffusion Applies a random pattern that is usually less noticeable than Pattern dither. The dither effects are
diffused across adjacent pixels.
• Pattern Applies a halftone-like square pattern to simulate any colors not in the color table.
• Noise Applies a random pattern similar to the Diffusion dither method, but without diffusing the pattern across
adjacent pixels. No seams appear with the Noise dither method.
Transparency and Matte Determines how transparent pixels in the image are optimized.
• To make fully transparent pixels transparent and blend partially transparent pixels with a color, select Trans-
parency and select a matte color.
• To fill fully transparent pixels with a color and blend partially transparent pixels with the same color, select a matte
color and deselect Transparency.
• To select a matte color, click the Matte color swatch and select a color in the color picker. Alternatively, select an
option from the Matte menu: Eyedropper (to use the color in the eyedropper sample box), Foreground Color,
Background Color, White, Black, or Other (to use the color picker).