Standard
JPEG (ISO/IEC 10918, ITU-T T.81) is a widely used lossy image compression standard using chroma subsampling and quantization, with tunable quality.
PNG-8 at 124 colors encoded a red-text test poster in 48,481 bytes at an edge error of 0.13 Delta E, smaller and cleaner than every JPEG export. For flat graphics like this one, an export tool that converts everything to JPEG ships bigger files with dirtier red text.
Reality
Chromium 149 canvas JPEGs grew 2.25x from quality 0.80 to 0.99 while red-text edge error fell only from 8.11 to 6.35, one developer measured. Firefox drops chroma subsampling at a lower setting, so the reviewer's browser decides whether the fringe shows.
Reality
Oizom replaced an hourly Python heatmap job with an on-demand Go service that renders 20 air-quality images in 30 ms. Per-function timing then traced 80% of each render to PNG encoding, on test images small enough to keep the interpolation cheap.
Reality
Headless Chrome 149 wrote the same 1,345,909-byte PNG via canvas.toBlob at quality 0.1 and at 1.0, one developer's measurements show. A PNG export slider only changes the file if the tool downscales, quantises colours or switches to WebP or AVIF.
Reality
A month of measured round trips on one handset found WhatsApp, Instagram and Facebook encoding on quantization tables the JPEG standard never described, while Telegram sent back a plain scaled Annex K near quality 87.
Reality
Real headers and an exact byte count pull against each other, and every format loses the fight differently. One generator author walked 25 of them and catalogued the bugs that browsers forgive and CI parsers refuse.
Reality
A browser image tool's writeup on binary-searching JPEG quality, and on PNG, where the quality-shaped proxy it searches cannot address 155 of the 255 available palette sizes.
Reality