The GIF format uses 8‑bit color and efficiently compresses solid areas of color while preserving sharp details like those in line art, logos, or type. You also use the GIF format to create an animated image and preserve transparency in an image. GIF is supported by most browsers.
The GIF format uses LZW compression, which is a lossless compression method. However, because GIF files are limited to 256 colors, optimizing an original 24‑bit image as an 8‑bit GIF can subtract colors from an image.
You can choose the number of colors in a GIF image and control how colors dither in a browser. GIF supports background transparency or background matting, by which you blend the edges of the image with a web page background color.
The PNG‑8 format uses 8‑bit color. Like the GIF format, PNG‑8 efficiently compresses areas of solid color while preserving sharp detail like those in line art, logos, or type.
Because PNG‑8 is not supported by all browsers, you may want to avoid this format when you are distributing the image to a wide audience.
The PNG‑8 format uses more advanced compression schemes than GIF does, and a PNG‑8 file can be 10% to 30% smaller than a GIF file of the same image, depending on the image’s color patterns. Although PNG‑8 compression is lossless, optimizing an original 24‑bit image as an 8‑bit PNG file can subtract colors from the image.
Note:
With certain images, especially those with simple patterns and few colors, GIF compression can create a smaller file than PNG‑8 compression. View optimized images in GIF and PNG‑8 format to compare file size.
As with the GIF format, you can choose the number of colors in an image and control how colors dither in a browser. The PNG‑8 format supports background transparency and background matting, by which you blend the edges of the image with a web page background color.
GIF is the standard format for compressing images with large areas of solid colors and crisp details like those in line art, logos, or type. Like the GIF format, PNG‑8 supports transparency and efficiently compresses areas of solid color while preserving sharp detail; however, not all web browsers can display PNG‑8 files.
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Under the optimization format menu, choose a color-reduction algorithm for generating the color lookup table:
Perceptual
Creates a custom color table by giving priority to colors for which the human eye has greater sensitivity.
Selective
Creates a color table similar to the Perceptual color table, but favoring broad areas of color and the preservation of web colors. This color table usually produces images with the greatest color integrity. (Selective is the default choice.)
Adaptive
Creates a custom color table by sampling colors from the spectrum appearing most commonly in the image. For example, an image with only shades of green and blue produces a color table made primarily of greens and blues. Most images concentrate colors in particular areas of the spectrum.
Restrictive (Web)
Uses the standard, 216‑color, web‑safe color table common to the 8‑bit (256‑color) panels of Windows and Mac OS. This option ensures that no browser dither is applied to colors when the image is displayed using 8‑bit color. If your image has fewer than 216 colors, unused colors are removed from the table.
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