Lossy or lossless? Compression explained simply

Two ways to make an image smaller

Every image compression wants the same thing: a smaller file. There are two fundamentally different ways to get there.

• Lossless: the image is packed more cleverly, without losing a single pixel. When opened, it's exactly as before — like a ZIP archive you unpack again. Formats: PNG, GIF, TIFF, lossless WebP.
• Lossy: the image is made smaller by permanently discarding information — mostly detail the eye barely misses. This saves far more space, but the original never comes back. Formats: JPG, lossy WebP and AVIF.

That's the whole core. Everything else follows from this one difference.

The analogy

Lossless is like a folded letter: you make it smaller, but every letter is preserved, and unfolded it's complete again. Lossy is like a summary of the letter: shorter, the gist is there, but the exact wording is gone — and you can't reconstruct the original letter from the summary.

Why JPG degrades on every save

An important everyday rule follows from JPG's lossy nature: every re-save of a JPG discards more information. Open, tweak slightly, save again as JPG — and new artifacts have crept in. Over many rounds a photo becomes visibly mushy. So: export as JPG once, at the end, and keep the original or a lossless format for intermediate steps. A PNG, by contrast, stays identical on every save — lossless means: as many times as you like, without loss.

Lossless is not "better"

A common misconception: that lossless is the higher quality tier. It isn't — it's a different category. Lossless preserves perfect quality, but for photos it produces three to ten times larger files than lossy. For a photo on the web that would be pure waste: the lossy-discarded part is invisible anyway. The choice is not a quality question but a purpose question.

Which type when?

The format decision in detail — including the grey areas — is covered in our JPG vs PNG article.

The formats that can do both

WebP and AVIF are hybrids: they handle both types, and you choose when saving. A lossy WebP replaces JPG (smaller), a lossless WebP replaces PNG (also smaller). This flexibility makes them good modern default formats — you just need to know which variant you're producing. JPG (lossy only) and PNG (lossless only) take the decision off your hands, but also box you in.

Conclusion

Lossless preserves everything but costs space; lossy saves space by discarding the invisible. Neither is "better" — each fits a purpose. Photos to lossy (JPG/WebP), graphics and archives to lossless (PNG/TIFF).