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Showing posts from March, 2015

Semi-transparent GIF images

Are you ready to return to the 1980's? Uh...me neither. But this post will take you back. And your head will hurt thinking about what I've done to the Internet.

Today, I was looking at this logo on the PHP website trying to figure out why it was so distracting:



And then, after digging around for a bit, I realized that the image was larger than it looked:



Then I realized that the browser was resizing the image to the smaller size. And then I realized that the first image looked a bit anti-aliased, which reminded me that a lot of web browsers will use bicubic scaling to resize larger images. I then realized that this behavior could be abused when applied to a 1-bit alpha channel. Such as the 1-bit alpha channels like those found in GIF images.

GIF is one of the oldest image file formats. It was invented in the late 1980's and is still used on the Internet today for some animations. One of the areas it has traditionally been weak in is transparency. PNG has large…