Oversized images waste bandwidth and storage. A single photo from a modern phone can be several megabytes, and a page with a handful of them makes every visitor download all that data. Pages load slower, mobile data runs out sooner, and hosting costs go up. Many email providers also cap attachments at around 20 to 25 MB. Compression removes data the eye doesn't need and keeps the image looking the same.
Each format compresses differently. PNG is lossless: it finds patterns in the data and stores them more efficiently without discarding anything. JPG is lossy and removes detail the eye barely notices. WebP and AVIF offer both lossy and lossless modes, and HEIC uses compression borrowed from video codecs. In every case the goal is a smaller file that still looks right.
These compressors run on your device with WebAssembly versions of MozJPEG, libwebp, libavif and oxipng, the same encoders many developers use in their build tools. Your images are never uploaded, so there's no upload wait, and any image that wouldn't get smaller is returned unchanged. For resizing and format choice in one step, use the image optimizer.
Frequently Asked Questions
What's the difference between lossless and lossy compression?
Lossless compression stores the same pixels more efficiently, so the original image can be reconstructed exactly; PNG works this way. Lossy compression discards some detail to reach much smaller sizes; JPG and most WebP and AVIF files work this way. Detail removed by lossy compression can't be recovered.
How much can I compress an image before quality degrades?
It depends on the image and how closely you look. Photos with complex scenes and textures hide compression better than simple graphics with sharp edges. Start at quality 80 to 85 for JPG and adjust while checking the preview. For PNG, a reduced color palette usually saves more than anything else.
Should I compress images before or after resizing?
Resize first, then compress. Resizing cuts the number of pixels, so the compressor has less to store and finishes faster. A 4000 × 3000 photo scaled to 1200 × 900 is a fraction of the size at the same quality setting. The image optimizer does both steps at once.
Does compression affect print quality?
Strong compression can show in print, especially in smooth gradients and flat colors. For print, use quality 90 or more, or a lossless format. Screens hide small artifacts better because of viewing distance and display size.
Compress images before you upload them anywhere. Websites load faster, email attachments go through, and storage lasts longer. Start around quality 80 and adjust based on what you see.