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Chapter 18. Optimization > JPEG Compression

JPEG Compression

JPEG is an acronym that stands for Joint Photographic Experts Group. It's a file format that was designed to reduce the file size of photographic images. Let's take a look at the general idea behind it. First off, JPEG is known as a lossy file format because it degrades the quality of the image each time it is saved. So what exactly does JPEG do? It separates your image into color and brightness information, and then degrades the quality of the color information while maintaining the quality of the brightness information.

To get a sense for how this affects an image, open any full-color photograph and then choose Filter > Blur > Gaussian Blur. Move the slider around and see how much you can blur (read: degrade) the image before you really notice it. It doesn't take much blurring before you can see a huge change in the image (Figure 18.1).


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