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Chapter 14. GIF Format > Transparency

14.7. Transparency

The GIF89a format introduced the ability to make portions of graphics transparent. Whatever is behind the transparent area (most likely the background color or pattern) will show through. With transparency, graphics can be shapes other than rectangles!

To understand how transparency works, you need to start with the color table (the table that contains the palette) for the indexed color image. In transparent GIFs, one position in the color table is designated as "transparent," and whatever pixel color fills that position is known as the Transparency Index Color (usually gray by default). All pixels in the image that are painted that color will be transparent when viewed in a browser.


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