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Compressed image size is bigger than original one #95

Answered by saucecontrol
h-alk asked this question in Q&A
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Hi Alex,

Without the source image, I can't say for sure, but it's likely the source image is encoded with optimized huffman dictionaries, which is something the built-in Windows JPEG codec doesn't do. In short, JPEG compression is done in two parts:

  1. Quantization of DCT coefficients. This is the part that is controlled by the Quality setting in JPEG -- lower qualities use higher quantization divisors, which "throw away" more of the source image data, making it a lossy format.
  2. Lossless entropy coding. This is more similar to Deflate/Zip compression where common patterns are compressed to shorter codes. JPEG can be compressed with either a standard dictionary that works reasonably well for …

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Converted from issue

This discussion was converted from issue #94 on September 19, 2022 16:17.