Compress AVIF Images

AVIF is already the most efficient, so there is less to take

AVIF compresses a photograph more efficiently than JPG or WebP, which means a file that is already AVIF is usually closer to what it needs to be than the same image in any other format. A moderate reduction is easy; a large one is not, because there is not much redundant information left to discard. That is the honest position: if an AVIF file is far larger than you need, the reason is usually the dimensions rather than the format, and resizing will help far more than further compression.

NoteA large AVIF is usually a large image, not an inefficient format. Resizing beats recompressing.

When resizing is the real answer

A 4,000 pixel wide AVIF used as a 1,200 pixel web image is carrying three times the pixels anyone will see, and no amount of recompressing at a sensible quality will remove that waste without visibly degrading the result. Resizing to the display width, or to twice that for high-DPI screens, removes the surplus at no quality cost and produces a much smaller file. This is the same principle as everywhere else in the site, but it matters more for AVIF because the format is already so efficient that quality has to fall a long way before the file gets small.

• A large image used small: resize. That is where the bytes are.
• A correctly sized AVIF that is still too big: recompress gently.
• Re-compress from the original, never from a previous AVIF.
• Keep the original at full resolution in case the layout changes.

NoteAn oversized AVIF is an oversized image. Resize it rather than degrading the quality.

The second lossy pass

AVIF is lossy, so the file you are compressing is already a reconstruction, and re-encoding discards more. One further pass is generally fine for web delivery. Repeatedly compressing the output is how an image degrades into visible mush, and because AVIF is already efficient the temptation to push the quality down further is stronger than with other formats. Keeping the original and compressing once from it is the discipline that avoids this.

• One further pass is acceptable for web use.
• Repeated compression compounds the loss visibly.
• Compress from the original, not from a previous output.
• AVIF holds more quality at a given size, so there is less to gain by pushing further.

Checking the result at the size it will be seen

AVIF holds up well at small display sizes, which means a file compressed fairly aggressively can look fine in a page and fall apart when zoomed. The useful test is to view the result at 100 percent, where banding in a gradient and softness around an edge become visible, and to compare it against the original at the same zoom. A difference that is obvious at 100 percent and invisible at normal viewing size is an acceptable trade, and one that is obvious at both is not.

• Check at 100 percent, where artefacts are visible.
• A difference obvious only when zoomed is usually acceptable.
• A difference obvious at normal size means the quality went too far.
• Compare against the original at the same zoom before accepting.

NoteAVIF holds up well small, so a heavy reduction can look fine in a page and fail under inspection.