How to compress images without losing quality

Lossy and lossless are two different jobs

A JPEG is lossy. It works by discarding detail your eye is bad at noticing — fine colour variation, more than fine brightness variation — and it does this every time it is saved. Push the quality slider low enough and you get blocky edges and muddy gradients, because there is no longer enough data to describe the smooth transition that was there.

A PNG is lossless. Saving it again cannot degrade it, because nothing is thrown away. That also means re-saving a PNG at "80% quality" is meaningless — the number has nothing to act on. The only way to make a PNG meaningfully smaller is to reduce how many distinct colours it stores, which is called palette quantization.

This is why a tool that treats every image the same way disappoints in one direction or the other: it either ruins photographs or does nothing at all to graphics.

Transparency is the thing you cannot get back

A JPEG has no alpha channel. None. So when a tool "converts your PNG to JPEG to save space", every transparent pixel gets filled in with a background colour — usually white, sometimes black — and that decision is permanent. Re-saving as PNG afterwards does not bring the transparency back; it just stores the white.

This is the single most common way people quietly ruin a logo. The file looks fine on the white page where they checked it, and wrong everywhere else.

CompressKits detects transparency before compressing and refuses to route a transparent image into a format that cannot carry it. If you explicitly ask for JPEG on an image with an alpha channel, you get the format that preserves it instead — you are never silently flattened.

Which setting should you actually pick?

Balanced is the right answer for almost everything. It targets the point on the curve where file size falls off sharply but visible quality barely moves — typically 60–80% smaller for a photograph, with nothing you would spot without flicking between the two at full zoom.

Choose High quality when the image will be printed, cropped into later, or used as a source you will edit again. Compression artefacts compound: each subsequent edit and re-save builds on the damage from the last one.

Choose Maximum compression for images headed straight to a web page or an email, where load time matters more than pixel-level fidelity and nobody will ever open the file at 400%.

One thing worth knowing: if your image is already well optimized, re-compressing it can produce a larger file. CompressKits checks for this and returns your original bytes instead, reporting an honest 0% rather than handing you something bigger and calling it a saving.