"Compress this image, but don't make it look worse." It sounds like a contradiction, but it is exactly what good compression delivers every day. The trick is understanding what compression actually does, and choosing settings that throw away only the data your eye will never miss. Done right, you can cut a file by 70% with no visible difference at all.
Compression is the process of encoding an image using less data. There are two fundamentally different approaches, and knowing the difference is the key to everything else.
Lossless compression reduces file size without discarding any image data. When you open the file, every pixel is restored exactly as it was. PNG uses this approach. The catch is that the savings are modest — usually 10–30% for typical images.
Lossy compression achieves much smaller files by selectively discarding information. The clever part is that it discards the data your eye is least sensitive to — subtle color shifts and fine detail in busy areas. JPG and WebP use this approach, and it is how a multi-megabyte photo becomes a couple hundred kilobytes that still looks excellent.
When you save a JPG or WebP, you choose a quality level, usually expressed as a percentage. This single number controls how aggressively the image is compressed, and getting it right is the whole game.
For the vast majority of web images, 80% is the number to remember. It reliably produces a file a fraction of the original size while looking, to the human eye, identical to the original.
The single most common mistake is starting too low. Begin at 80%, look at the result, and only drop the quality if you genuinely need a smaller file and can accept the trade-off.
Here is a step many people skip. A photo straight from a modern phone might be 4000 pixels wide — but if it will be displayed in a 800-pixel-wide column on your website, those extra pixels are pure waste. Resizing the image down to the size it will actually be displayed is often the single biggest file-size saving you can make, and it happens before compression even enters the picture.
The ideal workflow is: resize to the final display dimensions first, then apply compression. Doing both can easily take a 6 MB photo down to under 150 KB with no visible loss. Our Image Resizer and Image Compressor are designed to be used together exactly this way.
Compression and format go hand in hand. Compressing a logo as a JPG will introduce ugly artifacts around the text no matter how high the quality; it should be a PNG or lossless WebP instead. Compressing a photograph as a PNG will leave it needlessly huge; it should be a JPG or WebP. Pick the format that suits the image, then compress within that format. If you are unsure which to use, our guide to JPG, PNG and WebP breaks it down.
A few habits quietly degrade images. Avoid these:
Yes — positively, when done well. Page speed is a confirmed Google ranking factor, and images are usually the heaviest part of a page. Smaller, well-compressed images load faster, which improves your Core Web Vitals scores and keeps visitors from leaving. We cover this in depth in our image optimization and SEO guide.
The best way to build intuition is to experiment. Drop a photo into our free Image Compressor, slide the quality down from 100%, and watch both the preview and the file size. You will quickly see how far you can push it before the difference becomes noticeable — and for most images, that point is far lower than you would expect. Everything happens in your browser, so your photos never leave your device.
Master these few principles and you will never again have to choose between a fast website and good-looking images. You can have both.