Lossy vs Lossless Compression: What's the Difference?

Whenever you save or compress an image, you're using one of two approaches: lossy or lossless. It sounds technical, but the idea is simple, and understanding it is the key to getting small files that still look good. Here's the difference, without the jargon.

Lossless: keep every pixel

Lossless compression makes a file smaller without discarding any information — decompress it and you get back the exact original, pixel for pixel. It works by finding patterns and storing them more efficiently, a bit like zipping a document.

The upside is perfect quality; the downside is that the savings are modest. PNG is the classic lossless image format, ideal for graphics, logos, screenshots and anything with text or transparency where you can't afford any degradation.

Lossy: throw away what you won't notice

Lossy compression makes files dramatically smaller by permanently discarding information the human eye is unlikely to notice — subtle colour shifts, fine detail in busy areas. You can't get the original back, but at sensible settings you can't see the difference either.

JPEG is the classic lossy format, and it's why a photo can shrink from several megabytes to a couple hundred kilobytes. The trade-off is control: push compression too far and you start to see blockiness and blurring.

Which should you use?

Use lossy (JPEG, or WebP/AVIF in lossy mode) for photographs and any image where a small, invisible quality trade-off is worth a much smaller file — which is almost all web images. Use lossless (PNG, or WebP/AVIF lossless) for graphics with sharp edges, text, flat colours or transparency, where every pixel matters.

Modern formats like WebP and AVIF blur the line by offering both modes, so you can pick per image.

The practical takeaway

Don't think of lossy as "bad quality" — think of it as "adjustable quality." At 70–85% quality, lossy compression is visually indistinguishable from the original for most photos while being a fraction of the size. The skill is choosing the right level, and comparing before and after.

Our compressor lets you do exactly that: adjust the quality, watch the output size update live, and compare the result side by side — all in your browser, with nothing uploaded.