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Fixing JPEG’s “Photocopier Effect” problem

August 30, 2016

If you make a copy of a copy of a copy, the quality will deteriorate with each subsequent version in a phenomenon called “generation loss.” It’s easy to understand why this happens with actual copier machines. Scanning and printing are based on noisy sensors and physical paper and ink, and the resulting noise will tend to accumulate.

Digital images should not suffer generation loss. In theory, a file can be copied over and over again, and it should be bit-for-bit identical to the original. However, lossy image formats, such as JPEG, can behave like photocopiers. If you simply copy a JPEG file, nothing changes. But if you open a JPEG file in an image editor and then save it, you will get a different JPEG file. Some information can be lost in the process, and compression artifacts will start to accumulate. Do this often enough, and the image will eventually degrade beyond use.


The problems with resaving JPEGs

In this video, you can see what happens to image quality when you re-encode a JPEG image many times.