Compress images

Photographs go in JPG or WebP. Screenshots, logos and anything with flat colour or transparency go in PNG or WebP. If the file is for a website and you do not need to support software older than about 2020, WebP beats both.

That covers most decisions. The rest of this explains why, and what goes wrong when you pick the other one.

Lossy and lossless, which is the whole distinction

JPG, WebP and AVIF are lossy. They throw information away permanently and store an approximation. Done well you cannot see the difference, and the file is a fraction of the size.

PNG is lossless. Every pixel comes back exactly as it went in. Nothing is discarded, which is why it cannot get anywhere near the same size on a photograph.

This is why compressing a photo to PNG makes it larger rather than smaller, and it surprises people constantly. A 3MB JPG saved as PNG can come out at 12MB. PNG is not doing a bad job, it is doing a different job. It is preserving detail that JPG had already thrown away and that your eye was never going to notice.

The reverse is just as bad. A screenshot of text saved as JPG picks up a halo of smeared pixels around every letter, because JPG's compression assumes it is looking at a photograph where sharp edges are rare.

What to use, and when

JPG is right for photographs going anywhere at all. Every piece of software written in the last thirty years reads it, including print shops, old versions of Office and whatever a government upload form is running. It has no transparency.

PNG is right for screenshots, logos, diagrams, icons and anything with a transparent background. Flat areas of colour compress extremely well in PNG, so a logo can be smaller as PNG than as JPG and look sharper.

WebP is right for the web. It does both jobs: lossy for photos, lossless with transparency for graphics, and it is typically 25 to 35 percent smaller than JPG at the same visible quality. Every current browser reads it. Older desktop software often does not, so it is a poor choice for a file you are emailing to somebody.

AVIF compresses better still, often another 20 percent below WebP, and browser support is now broad. It is slower to encode and support outside browsers is thinner. Worth using when the saving matters more than universal compatibility.

Quality settings, and where the money is

Quality on a lossy format is not a percentage of anything meaningful. It is a dial on how aggressively detail is discarded, and the relationship between the number and the file size is steep at the top.

Between 75 and 85 you get most of the saving for a difference you will struggle to see on a photograph. Above 90 the file grows fast in exchange for detail your eye is not collecting. At 100 a JPG can be double the size of the same image at 92 and look identical.

Below about 60 it starts to show, first in areas of subtle gradient like skies and skin, where you will see banding and blocky patches.

Compression is not reversible. Once the detail is gone it does not come back, and saving a compressed file again compresses what is left. Keep the original if the image might need editing later.

Dimensions usually matter more than quality

The single biggest thing people miss: a 4000 pixel wide photo displayed in a 800 pixel wide column is carrying five times the pixels it needs. Dropping the dimensions saves far more than any quality setting, and costs nothing visible because those pixels were never being shown.

If a photo is going on a website, resize it first, then compress. Doing it the other way round means you carefully compressed pixels you were about to throw away.

What compression cannot fix

It cannot sharpen a blurry photo, recover a blown out sky, or add detail that the camera did not capture. Compression only ever removes.

It also cannot make a badly chosen format behave. If your PNG of a photograph is enormous, no amount of PNG compression will fix it, because the problem is the format rather than the settings.

A quick table

You have	Going where	Use
Photograph	A website	WebP, or AVIF
Photograph	Email, print, an upload form	JPG
Screenshot or logo	Anywhere	PNG
Logo with transparency	A website	WebP
Anything	Editing later	Keep the original too