Field guide
Sometimes the format is doing the work
A smaller file can come from choosing a representation suited to the pixels. Compression settings cannot rescue a format that describes the content inefficiently.
01
JPEG suits continuous-tone photographs but introduces ringing around text and hard graphics. PNG preserves those edges exactly and can be much smaller when large areas repeat.
02
WebP can encode photographic and lossless content, yet compatibility requirements still matter for older publishing systems and document portals.
03
Transparency rules out ordinary JPEG unless the empty area is intentionally flattened onto a chosen colour. A white default may be wrong for dark interfaces or later compositing.
04
Test representative images rather than one convenient sample. A logo, portrait and noisy night photograph expose very different strengths in the same encoder.