What is Compression artifacts?

Compression artifacts

Compression artifacts are the visible defects lossy compression leaves behind when quality is pushed too low: blocky 8x8 patches in smooth areas, ringing halos around text and hard edges, banding in gradients, and smeared fine detail. They're permanent once saved - the only fix is returning to a better-quality original.

Recognizing the common types

Blocking shows up as a faint mosaic grid in skies and shadows. Ringing appears as ghostly echoes hugging high-contrast edges - the classic 'fuzzy text on a screenshot' look. Banding turns smooth gradients into visible stripes. Color bleeding smudges saturated edges because color detail is compressed harder than brightness.

Avoiding them

Keep photographs at sensible quality settings (around 75-90% covers most uses), never re-save a JPG repeatedly, and don't put text or line art through lossy compression at all - use PNG for those. If a file already shows artifacts, recompressing it smaller only compounds them.