Image compression: how to get a file small enough
What compression actually does
Lossy compression, as used for JPG, throws away detail you are unlikely to notice, such as tiny colour variations. The quality slider controls how much. Lower numbers give smaller files and, eventually, visible blockiness.
Getting to a target size
Upload forms often ask for under 100 KB, 200 KB or 500 KB. Because the result depends on the picture, aim for it in steps: compress at 70, check, then adjust. A very large camera photo is best resized first, then compressed.
Email, chat and data costs
Gmail limits attachments to 25 MB in total, and smaller images upload faster on slow or expensive mobile data. A folder of compressed photos can be a fraction of the original size.
Websites and ranking
Heavy images are a common cause of slow pages. Google’s Largest Contentful Paint guideline for a good score is 2.5 seconds or less, and the main image is frequently the element measured.
What you give up
The output is always a JPG. Transparent areas become white and animated GIFs lose their animation. If you need transparency, keep the PNG.
Compare the before and after at full size. If you cannot tell them apart, you can probably go a notch lower.