: When resaving JPEGs, the file size increases, but the quality is not changed – why? I was experimenting with JPEG quality loss upon resaving and noticed that not only (even after four resaves)

@Ogunnowo857

Reason 1: Additional Meta Data

Use a tool like ImageOptim to get rid of all meta data and check the file size again.

If all files are (quite) the same size after removing meta data, you know where the extra bytes are.

A color profile might also be part of the file and therefore add some bytes.

Reason 2: Compression Artifacts

Saving an image with JPEG compression adds artifacts to the file. Even if they are not visible in the first place, the image data is different. Compressing an image with artifacts again, generates more artifacts and so on.

In this case, JPEG compression is not as effective as with the original file. The more artifacts are contained, the bigger the file will be.

Visualization of JPEG artifacts in your image



Technical details

If you are interested in the technical details, you might want to read this article:
JPEG compression algorithm

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