Lossy vs lossless image compression: what is the difference?

Image compression makes files smaller. It comes in two kinds, and the difference decides how much you can save and what you give up.

Lossless compression

Lossless compression stores the same pixels in fewer bytes, like zipping a document. When you open the file you get exactly what you saved. PNG is lossless. The savings are modest for photos and larger for flat graphics with repeated colours.

Good for: logos, line art, screenshots, anything with text or sharp edges, and images you will edit again.

Lossy compression

Lossy compression removes detail that people are unlikely to notice, mostly fine texture and subtle colour changes. JPG is lossy, and WebP and AVIF can be. Savings can be dramatic, and quality drops as you push harder. Every time you re-save a lossy file the loss repeats, so keep an original.

Good for: photographs and anything shown on screens where size matters.

What the quality slider does

The quality number controls how much detail is discarded. Roughly:

• 90–100: near-identical to the original, larger files.
• 70–85: a strong balance for web and email.
• below 60: visible artefacts, especially around edges and text.

Palette PNGs: a middle path

You can shrink a PNG by reducing its colour palette. It is technically lossy because colours are merged, but it keeps transparency and sharp edges, which suits logos and illustrations.

How to choose

1. Photo → lossy (JPG, WebP, AVIF).
2. Logo or screenshot → lossless PNG, or WebP lossless.
3. Need an exact file size → lossy, then check the result.

See it for yourself

Drop a photo in the tool below and move the quality slider while watching the before/after view. Stop when you can first see a difference, then go one step higher. For graphics, try Compress PNG.