Everything about JPEG

An encoder gives the hedge behind your subject as many bits as the subject. A saliency model knows better, but a browser will not let you set quality per region, so the encoder is not steered: its input is prepared instead. On the sample that was 41 per cent off the file at an unchanged quality setting.

JPEG damage is not random. It is made in blocks of eight by eight pixels, in a known order, which is why a model trained on compressed images beats any amount of sharpening. It runs in your browser, repairs at four times the size and hands the result back clean.

WordPress has allowed .heic uploads since 6.7 and converts them to JPEG on the way in, but only when the server has a HEIC-capable Imagick. Here is what core actually does with the file, why the same site answers differently through a browser and through WP-CLI, and which fix stops the problem instead of managing it.

An enormous amount of what people need to see is a picture of a screen, and most of those pictures are worse than they need to be for reasons that take seconds to fix.

Quality 80 means one thing in JPEG, another in WebP, and something different again on a screenshot than on a photograph. Here is what the number actually sets, what SSIM can and cannot tell you, and how to find the point where your own file stops getting meaningfully smaller and starts getting visibly worse.

Every photograph carries a block of tags nobody looks at: camera, lens, exposure, three timestamps, and often the coordinates of the room it was taken in. Read yours in the browser, then learn what each field means, who wrote it, and what quietly removes it.

The photograph looked right in your editor and flat on the site. Here is where WordPress and its plugins drop the colour profile, and the export habit that ends it.

WordPress keeps the file you uploaded exactly as it arrived, sitting next to the resized copies it actually serves. If that file came off a phone, it very likely still carries the coordinates of the room it was taken in.

Two thirds of this site's media library is PNG, and nobody decided that. What WordPress actually does with an uploaded file, what its default encoder quality really is, and the three filters that change the format and the size of every sub-size it writes.

Blurry WordPress images are not one problem but six, and each leaves a different fingerprint. Work out which symptom you have before you change anything, because most of the fixes do nothing for most of the causes.