Images: free online tools

7 free tools, processed locally in your browser.

Seven tools, three families. Change the format: PNG → JPG, WebP → PNG, HEIC → JPG. Change the dimensions or the framing: Resize image and Crop image. Act on the weight or the content: Compress image and Remove background. A photo that is simply too heavy usually belongs to two families at once, which is where resizing and compressing get confused with each other.

The distinction is a clean one. Resizing throws pixels away: a photo 4000 pixels wide brought down to 1200 loses three quarters of its surface for good. Compressing keeps the same dimensions and works on the encoding instead. For an image headed to a web page, the efficient order is to crop, resize to the width it will really be displayed at, then compress.

Tools in the Images category

Choosing between the format converters

PNG → JPG is aimed at screenshots and at photos saved as PNG by mistake. Transparency does not exist in JPG, so the tool replaces it with a white, black or light grey background, to be chosen before the conversion. On a logo or a flat colour graphic, the JPG produced can weigh more than the PNG you started from, and the message shown under the result tells you so: keep the PNG in that case.

WebP → PNG answers the opposite problem, a modern image that an older program refuses to open. The PNG you get back will be bigger; that is the price of compatibility. HEIC → JPG handles iPhone photos through the heic2any library, with a quality slider from 50 to 100 per cent. Always run this conversion first: the other tools rely on the browser’s own decoder, which does not read HEIC outside Safari.

Resize, crop, compress

Resize accepts pixels or a percentage, and displays the original dimensions as soon as the file is dropped in. The box that keeps the proportions prevents stretching; the reduction is carried out in successive steps, which limits the jagged look on large factors. Enlarging is allowed, but no detail absent from the original is going to be invented.

Crop works on a preview capped at 640 pixels wide, on which you draw the area to keep; the real dimensions of the selection update continuously. The Free, 1:1, 16:9, 4:3 and 3:4 chips lock the ratio, which is useful for a profile picture. Compress accepts JPG, PNG and WebP in batches, with quality adjustable from 30 to 95 per cent.

Which engines, and which trade-offs

Compression relies on three codecs compiled to WebAssembly: MozJPEG for JPG, libwebp for WebP, OxiPNG for PNG. The last of these works without loss, every pixel coming out identical, which is why the gains are more modest on photographic images. The format selector then lets you push a heavy PNG over to JPG or WebP. If the result exceeds the weight of the source, the file you dropped in is kept instead.

All of these operations go through a decode to raw pixels followed by a re-encode. One consequence to know about: the photo’s EXIF metadata, including the capture date and the GPS coordinates, is not copied into the file produced. A loss for a photographer sorting through a shoot, an advantage before publishing anything online.

The quality slider sits at 75 per cent by default and moves in steps of five, which is the usual compromise for a photo headed to a web page; 85 to 90 is the range to hold for an image that will be printed or retouched afterwards. Lossless PNG optimisation typically returns thirty to sixty per cent, no more, and several files can be dropped in at once, the batch coming back as a ZIP archive.

Cut-outs and edge cases

Remove background does not recognise the subject: it reads the colours of the four corners, then makes transparent whatever is close to those shades and connected to the edges. A plain, contrasting background gives a clean result; a landscape or a texture does not. The tolerance slider corrects the two usual failures: lower it when the cut-out bites into the subject, raise it when patches of background survive. The output is always a PNG with an alpha channel, and images above roughly 24 megapixels are refused, which is one more reason to shrink a camera file before cutting it out.

One last reflex worth acquiring: check what output format to expect. Resize and Crop return a PNG when the input was a PNG, and a JPG in every other case.

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