Culture · 6 pages · 12 min
How compression makes a JPEG blocky
JPEG handles a picture in small blocks, and hard compression lets those blocks show.
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From the opening
JPEG compression goes blocky because it works on small squares, classically eight pixels on a side, and strong compression makes those squares disagree with their neighbors. The block is not a stain added later, but the unit of the method, visible once too much information inside each unit was discarded. The opening covers squares of eight pixels, coarse storage of fine patterns, and color kept at lower detail.
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Inside
- Squares of eight pixels
- Coarse storage of fine patterns
- Color kept at lower detail
- Smooth skies show the grid
- Where the idea stops applying
- A distinction worth keeping
Sources
- JPEG discrete cosine transform on eight-by-eight blocks
- Quantization and chroma subsampling in lossy JPEG