How image compression works
JPG and WebP can store a photo in much less space than a PNG. A lower quality number means a smaller file and slightly softer detail. Quality 80 is a practical default for photos.
If you need the file under a limit, such as 200 KB, turn on the target size. The tool tries qualities from 85 down to 40 and keeps the sharpest one that fits. It will not go below 40, so you get a clear message instead of a blotchy image.
Need a different format without shrinking on purpose? Use the image converter. Need an exact pixel size? Use the image resizer.