JPEG compression — Input checklist

Worked example

Before compressing a JPEG, record its byte size and pixel dimensions, and check whether it has already been squeezed by an earlier save.

Imagine an estate agent whose 12-megapixel phone photos, 4032 × 3024 px, are rejected by a listing form with a size cap. Write down the current weight and the cap first. Compression here keeps the pixel dimensions, so if the form also wants a smaller picture you will need Resize as a separate step.

Where the JPEG came from matters. A photo forwarded through a chat app or saved from a web page has usually been recompressed once already, so a further drop to quality 60 will pile new blocks on top of old ones. Prefer the camera original, and if you only have the forwarded copy, stay near 85 to 90 and accept a smaller saving.

Content decides how far you can go. Smooth skies, white walls and skin show banding and blotches early, while leafy trees, gravel and crowds hide artefacts well. A listing photo of a plain white kitchen is far less forgiving than a garden shot at the same quality number.

Do one concrete check: zoom the original to 100 percent on a wall or sky patch and on a text sign, and note how clean they are. You will compare those same spots after compressing. The file must also stay below 64 million pixels, and an image the browser cannot decode, such as many HEIC files, must first be converted to JPG.

JPEG photograph; original retained

JPEG export; compare bytes and edges

The tool re-encodes through the browser, so the original metadata, including GPS tags, is not carried into the compressed file.