Adobe Photoshop CS6, User Manual

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Example of Pattern Transparency dithering (left) and applied to a web page background (right)
Interlace Displays a low-resolution version of the image in a browser while the full image file is downloading. Interlacing can make downloading
time seem shorter and can assure viewers that downloading is in progress. However, interlacing also increases file size.
Web Snap Specifies a tolerance level for shifting colors to the closest web palette equivalents (and prevent the colors from dithering in a browser).
A higher value shifts more colors.
Optimize transparency in GIF and PNG images
Transparency makes it possible to create nonrectangular images for the web. Background transparency preserves transparent pixels in the image.
This allows the background of the web page to show through the transparent areas of your image. Background matting simulates transparency by
filling or blending transparent pixels with a matte color that can match the web page background. Background matting works best if the web page
background is a solid color and if you know what that color is.
Use the Transparency and Matte options in the Save For Web & Devices dialog box to specify how transparent pixels in GIF and PNG images are
optimized.
(GIF and PNG
-
8) To make fully transparent pixels transparent and blend partially transparent pixels with a color, select Transparency 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.
(GIF and PNG - 8) To make all pixels with greater than 50% transparency fully transparent and all pixels with 50% or less transparency fully
opaque, select Transparency and select None from the Matte menu.
(PNG - 24) To save an image with multilevel transparency (up to 256 levels), select Transparency. The Matte option is disabled since
multilevel transparency allows an image to blend with any background color.
Note: In browsers that do not support PNG
-
24 transparency, transparent pixels may be displayed against a default background color, such
as gray.
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 Color (to use the color in the eyedropper sample box), Foreground Color, Background Color, White, Black, or Other (to use the color
picker).
Note: The Foreground Color and Background Color options are only available in Photoshop.
View the color table for an optimized slice
The color table for a slice appears in the Color Table panel in the Save For Web & Devices dialog box.
Select a slice that is optimized in GIF or PNG - 8 format. The color table for the selected slice appears in the SaveFor Web & Devices color
table.
If an image has multiple slices, the colors in the color table may vary between slices (you can link the slices first to prevent this from happening). If
you select multiple slices that use different color tables, the color table is empty and its status bar displays the message “Mixed.”
Customize the color table for GIF and PNG - 8 images
You use the color table in the Save For Web & Devices dialog box to customize the colors in optimized GIF and PNG
-
8 images. Reducing the
number of colors often preserves image quality while reducing the file size of the image.
You can add and delete colors in the color table, shift selected colors to web - safe colors, and lock selected colors to prevent them from being
dropped from the palette.
Sort a color table
Choose a sorting order from the Color Tablepalette menu:
Unsorted restores the original sorting order.