Compress Image

Images are almost always the heaviest thing a web page loads — routinely more than the HTML, CSS and JavaScript put together. That makes them the dominant factor in Largest Contentful Paint, the Core Web Vital that measures how long a visitor waits before the main content appears. Halving your image weight typically does more for perceived speed than any amount of code optimisation.

The cost is not only speed. Most of the world browses on mobile data, and an uncompressed hero image spends someone's data allowance to deliver detail their screen cannot resolve. A 4 MB photograph displayed in a 800-pixel-wide column is delivering roughly ten times the information the display can use.

Compression is the cheapest of the available fixes because it requires no change to your layout, your markup or your workflow. The image looks the same and weighs a fraction as much.

JPG and WebP are lossy. They analyse the image, discard information the human visual system is least sensitive to — mostly fine colour variation — and store what remains. That is why they achieve such large reductions on photographs, and why pushing the quality too low produces the blocky halos you see around high-contrast edges.

PNG cannot work that way; it is lossless by definition, so it shrinks by reducing how many distinct colours the image uses. Our PNG path quantises the palette and dithers the result, which is essentially invisible on logos, screenshots and flat illustration, and quite visible on a photograph with a smooth sky. Setting the quality to 95% or above keeps PNG perfectly lossless and simply optimises the encoding.

This is why the format matters as much as the slider. A screenshot compressed as JPG will look worse and weigh more than the same screenshot as an optimised PNG, and a photograph stored as PNG will be several times larger than it needs to be.

WebP produces the smallest file at a given quality and supports transparency, and every current browser decodes it. It is the default choice for anything going onto a web page.

JPG is slightly larger but universally accepted, including by software that has never heard of WebP. Choose it for email attachments, upload forms, print services and anything leaving the web.

PNG is the right answer for sharp-edged content — logos, line art, screenshots, diagrams — and for anything needing transparency preserved losslessly. Do not use it for photographs unless you have a specific reason.

Sometimes the tool hands your original back and says so. That is deliberate: if nothing we can produce beats the file you supplied, returning a larger 'compressed' version would be a failure dressed up as a result.

It usually means the image has already been through an optimiser, or that it is a small graphic where the format's fixed overhead dominates. Very small PNGs in particular have a floor below which the header and palette are most of the file. In those cases the remaining wins are elsewhere — resizing to the dimensions actually displayed, or switching format entirely.