Normally, when you save a GIF or PNG-8 file that has semitransparent pixels in its original image, those pixels are blended with your selected Matte color to become fully opaque. That's how you can
"fake" a soft edge with a GIF or PNG-8 file: by using a Matte color that's the same as your web page's background color.
But if your background color isn't solid, such as with a pattern or photographic background, selecting a Matte color can be difficult because the edges become apparent when the transparent graphic is placed on the patterned background. So instead, turn on transparency dithering to dither those partially opaque areas.
TRY IT To turn on transparency dithering, first follow the steps in the preceding tip to optimize a transparent graphic. Then, change the option in the Transparency Dithering menu from No Transparency Dither to one of the other three options:
• Diffusion Transparency Dither To use a random "spattering" pattern that also affects adjacent pixels to lessen the appearance of the dithering
• Pattern Transparency Dither To use a square, halftone-like pattern
• Noise Transparency Dither To use a random "spattering" pattern that doesn't affect adjacent pixels and may seem more visible
For Diffusion Transparency Dither, specify the amount of dithering in the slider to the right.
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