Compress an image

Resize before you compress

This is the saving almost everybody leaves on the table. A photograph straight off a camera is often 4000 pixels wide, and the place it is going shows it at 800. Those extra pixels are decoded by every visitor and then thrown away by the browser.

Dropping the width to what the page actually uses saves more than any quality setting will, and unlike quality it costs nothing visible. Set the size first, then worry about the slider.

Changing format beats dragging the slider down

The second biggest saving is the format, not the compression. On our own photographs, WebP came out 14 to 20% smaller than JPEG at a comparable look, and AVIF came out 57 to 58% smaller, which is roughly three times the saving WebP gave.

So a WebP at quality 80 will usually beat a JPEG at quality 55, and it will look considerably better doing it. If the file is going on a web page, change the format and leave the quality alone. The full comparison against JPEG, PNG and AVIF has the measurements and the files they came from.

How far down the quality can go

Between 70 and 80 is the usual working band, and this page starts at 70. Most photographs survive it without anyone noticing.

Below about 60 the artefacts start showing, and they show first in the places people look hardest: skin, skies, and any smooth gradient. Detailed scenes with lots of texture hide compression well. A portrait against a plain wall does not. Watch the preview rather than trusting a number.

Why compressing matters beyond the file size

Page speed is one of the few image decisions a search engine measures directly, and images are usually the heaviest thing on a page. This is the cheapest performance work available, which is most of what actually affects image SEO, alongside the filename and the alt text.