Compress3 min read
How to reduce image size without losing quality
Measured file sizes at quality 90, 75 and 60, and JPG against WebP and AVIF at settings that look the same, so you can shrink images without visible damage.
Most photos are much bigger than they need to be. A phone photo of 2 to 5 MB can usually lose three quarters of its size before anyone can see a difference. The trick is knowing which setting to move and how far.
Every number below was measured with Compress image in a browser, on two files: a 3264 by 2448 landscape photo (2.6 MB) and our 2400 by 1600 test image (1.4 MB), a gradient with heavy grain added.
Quality is the main dial (link to section)
Quality decides how much fine detail the encoder keeps. These are the results at three common settings.
| Quality | Landscape photo (2.6 MB) | Test image (1.4 MB) |
|---|---|---|
| 90 | 1.5 MB (−44%) | 776 KB (−45%) |
| 75 | 468 KB (−83%) | 141 KB (−90%) |
| 60 | 326 KB (−88%) | 54 KB (−96%) |
The big drop happens between 90 and 75. Going from 75 to 60 saves much less, and that is where artefacts start to show around edges and in skies. For most photos, 75 is the sweet spot.
The format matters as much as quality (link to section)
Newer formats store the same picture in fewer bytes. We saved the landscape photo as JPG, WebP and AVIF at settings that looked the same to us at full size.
| Format | Setting | Size | Compared with JPG | Encode time |
|---|---|---|---|---|
| JPG | quality 75 | 468 KB | — | 0.8 s |
| WebP | quality 75 | 267 KB | −43% | 0.8 s |
| AVIF | quality 50 | 125 KB | −73% | 3.3 s |
AVIF quality numbers run on a different scale, so AVIF 50 is not "worse" than JPG 75. At 100 percent zoom the AVIF file was a touch softer in the distant hills, and otherwise hard to tell apart. If you want to stay safe, AVIF 60 gave 200 KB, still less than half the JPG.
WebP works in every current browser. AVIF works in current Chrome, Edge, Firefox and Safari, but some older apps and upload forms still reject it, so check where the file is going.
A method that works (link to section)
Resize first if the image is huge (link to section)
A photo shown 1200 pixels wide on a page does not need 4000 pixels. Halving the width cuts the pixel count by three quarters, which saves more than any quality setting.
Start at quality 75 (link to section)
Compress, then open the compare view at 100 percent. Look at faces, text, fine lines and smooth skies.
Adjust in steps of 5 (link to section)
If it looks perfect, try 70 or 65. If you see blocks or halos, go back up. Stop at the lowest setting you cannot tell apart from the original.
Try WebP or AVIF (link to section)
If the file is for the web, switch the format. It is often the single biggest saving, with no change in how the image looks.
When not to compress (link to section)
Keep the original for anything you may edit again, print large, or archive. Each lossy save throws away a little more, and the loss adds up. Compress a copy for sharing, and keep the master as it is.
PNG screenshots and graphics are a special case. PNG is lossless, so compressing it only repacks the same pixels. If a PNG is too big, save it as WebP or reduce its colours instead.
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