Quality or target size
With Quality, you choose how much detail to keep. Between 70% and 80%, most photos look the same as the original at normal viewing size while the file shrinks a lot. Below about 60%, you start to see blockiness around edges and in skies.
With Target size, you set the largest file you can accept, which is handy when a job portal, exam form or visa site says “under 200 KB”. The tool tries different qualities and keeps the highest one that fits. If even the lowest sensible quality is too big, it tells you, and the fix is to choose a smaller maximum size so there are fewer pixels to store.
Resizing makes the biggest difference
A 12-megapixel phone photo is about 4000 × 3000 pixels, far more than any screen shows. Shrinking it to 1920 pixels on the long side keeps it sharp on a laptop and cuts the file size by around three quarters before compression even starts. Sizes are never enlarged, and the shape of the photo is always kept.
Which format to choose
| Format | Best for | Transparency |
|---|---|---|
| JPG | Photos, and anywhere you are unsure what is accepted | No |
| WebP | Websites; often 25% to 35% smaller than JPG | Yes |
| PNG | Screenshots, logos and text; lossless | Yes |
If you save a transparent PNG as JPG, see-through areas are filled with white and the tool tells you. PNG ignores the quality setting because it never throws detail away. If a file would come out bigger than the original, you get the original back unchanged.
Private by design
Photos are compressed on your own device in a background worker, so they are never uploaded and large photos do not freeze the page. Photos taken on a phone are turned the right way up. iPhone HEIC photos can only be opened by browsers that support them, such as Safari; elsewhere, share the photo as JPG first.