Quality is an instruction, not a percentage kept
The number controls the browser encoder's trade-off between prediction error and file weight. Eighty does not mean eighty per cent of the original information, and the same number produces different savings on a portrait, a screenshot and foliage. That is why the result is encoded and measured before the download button becomes available.
When WebP earns its place
Photographs and mixed web graphics often land below comparable JPEG or PNG files, especially when transparency is needed. An already efficient WebP can grow after another encode; a negative difference in the ledger is the signal to keep the source rather than saving the new file.
The browser is the encoder.
Different browser engines can write slightly different bytes at the same quality. The probe verifies the format and the ledger reports the actual result; neither implies bit-for-bit reproducibility elsewhere.
Other compression mechanisms
- JPEG qualityInspect the quality floor and each measured trial.
- PNG compressionSeparate lossless re-deflate from palette reduction.
- A cap in KBSearch for the strongest result that fits below a stated limit.
- Batch compressionRun a queue with one ledger row per file.