Image Compressor

Lossy and lossless are different promises

Lossless compression rewrites the file so it takes less space while every pixel stays bit-for-bit identical. PNG works this way. The saving is real but modest, usually somewhere between five and thirty percent depending on how repetitive the image is.

Lossy compression throws information away — it keeps what the eye notices and discards what it does not, which is how JPEG and WebP reach reductions of eighty percent or more. The discarded data is gone permanently. Compressing the same JPEG repeatedly degrades it each time, which is why you should always compress from your original file rather than from a copy you already compressed.

Why the same setting gives wildly different results

Compression works by finding redundancy, and different pictures contain very different amounts of it. A photograph of a clear sky is largely smooth gradient, so it compresses enormously. A detailed forest scene with texture in every pixel has almost no redundancy and barely shrinks at the same quality setting.

Flat graphics behave differently again. Logos, screenshots and diagrams have large areas of identical colour and hard edges, and JPEG handles hard edges badly — it produces visible fringing around text. For that kind of image, PNG or WebP will be both smaller and cleaner than a JPEG at any quality you would accept.

Choosing a format

Use JPEG for photographs when you need something that opens everywhere without a second thought. Use PNG when you need transparency or when the image is flat graphics and text. WebP is smaller than both at comparable quality and is supported by every current browser, which makes it the sensible default for the web. AVIF compresses even harder, particularly at low bitrates, at the cost of slower encoding.

The practical rule is that the format matters more than the quality slider. Converting a screenshot from JPEG to PNG will usually beat any amount of JPEG tuning, and moving a photo from JPEG to WebP typically saves another quarter of the file for no visible change.

What compression cannot do

It cannot recover detail that is not there. An image that was upscaled from a small original contains no extra information, and compressing it simply makes a soft image smaller. Nor can it fix an image that was saved at low quality once already — the artefacts are now part of the picture and the encoder treats them as detail worth preserving.

It also will not reduce the pixel dimensions. If a 6000-pixel-wide camera file is destined for a web page that displays it at 1200 pixels, resizing it first will save far more than compression ever will, and the result will look better.

Why this runs in your browser

The compression happens on your own device using the browser's built-in image encoders. Nothing is uploaded, so there is no queue, no file-size limit imposed by a server, and no copy of your image sitting in someone else's storage. For photographs of documents, ID cards or anything else you would rather not hand to a stranger, that distinction matters more than a few kilobytes.