Convert pictures online

Most format advice is written about somebody else’s picture. An article that says WebP is twenty-five per cent smaller than JPEG is reporting an average over a corpus that does not contain your file, and averages are a poor guide to a decision about one photograph of one thing in one light.

So this runs the comparison on your file instead. It decodes it once, then writes it into each candidate format, searching that encoder’s own quality parameter until the result measures within the distance you asked for. What comes back is the size of the file that search produced, which is a fact rather than an estimate.

The download is the last and cheapest step. If the numbers say your original is already the best version of itself, the page says so and there is nothing to save — which is the one outcome a converter is least inclined to suggest and the most useful one it has.

The matrix on the left has a row for every file and a column for every format this browser can write. Each cell is the length of the file that encoder actually produced, with a bar against the largest in the row; the filled cell is the one the file will leave as. Click any cell — or move to it with the arrow keys and press Enter — to pin that format for that one file.

The Result panel carries the rest of the numbers for the file on the stage. Setting is the quality the search landed on — a result, not a knob you set, unless you switched quality to Fixed. Measured is how close the produced file is to your source on the structural-similarity scale, where 1.0000 is indistinguishable by that measure. Every note about the file — a name that lies about its format, an animation, a colour profile, a GPS position — is listed under it.

The stage is there because a number can only take you so far. Split puts your original and the converted file on either side of a divider you can drag, zoom goes to 800 per cent, and holding the space bar shows your original for as long as you hold it. What the Result side shows is the converted file itself, so what you judge is what you save.

Whatever this browser can decode: JPEG, PNG, WebP, GIF, AVIF, BMP and ICO almost everywhere, TIFF and HEIC where the browser has a decoder of its own — Safari does. The empty converter shows the answer for your browser, tested on the spot, and so does the format support page. The format is worked out from the bytes at the start of the file, never from the name, because a file called photo.jpg is under no obligation to be one. A file that will not open stays in the list, set apart, with the reason.

Some things it deliberately will not do. It does not edit: the pixels that come out are the pixels that went in, re-encoded, and shrunk on the way out only if you ask. It does not enlarge. A target in kilobytes belongs to one job only — a form that states one — and the form mode handles it, with sourced presets and a pass or fail line for every file.

Very large pictures are offered on a lighter working copy rather than refused outright, and the page says when it is working from one. Anything above the hard ceiling is declined with the actual number in the message.

There is more on the measurement itself in what quality really means, and a reference page for each format with its support table and its failure modes.