Resize Images Online

How it works

Each file is decoded into a bitmap, drawn into a canvas at the new size, and re-encoded. Three parts of that are worth explaining, because they are where resizers differ.

Choosing the target size. Width and Height modes take one dimension and compute the other from the source ratio, so the result is never distorted. Fit inside box scales until the whole image sits inside the rectangle you gave — usually leaving one dimension short of the number you typed, which is correct rather than a bug. Fill box does the opposite: it scales until the box is covered and crops the overflow from the center, guaranteeing exact dimensions at the cost of some edges. Exact size forces both numbers and is the only mode that can distort; it is last in the list for that reason.

Stepping down. Sampling a 4000-pixel-wide image directly into 200 pixels takes roughly one source pixel in twenty and discards the rest. Thin lines break up and fine textures sparkle. Halving repeatedly instead means every source pixel contributes to an average at each stage, and the final image looks the way you would expect. The tool calculates how many halving passes a given reduction needs and applies them automatically.

Orientation. Photos taken with a phone held sideways are stored the right way up with a rotation flag attached, not rotated on disk. Decoding without honoring that flag produces sideways output — and only for the pictures that happen to have been shot in portrait, which is why the bug survives so long in so many tools. Images here are decoded with orientation applied.

When you'd use this

The everyday case is a content management system or forum with an upload limit, where a 4 MB phone photo is refused and a 1200-pixel version sails through.

Batch work is the other. Product photos, a folder of screenshots for documentation, or event pictures that all need to be the same width are tedious one at a time and trivial in a batch. Because each result is listed separately with its own dimensions and size, you can see immediately if one file behaved differently from the rest — usually the one that was portrait when the others were landscape.

There is also the deliberately awkward case: an avatar or thumbnail slot that demands an exact square from images that are not square. Fill box handles this without you having to crop each one by hand first, and it crops from the center, which is right far more often than not.

What happens to your photo

It is uploaded, resampled here, and deleted. Being specific about that is worth more than a reassuring sentence.

The resampling runs on our server because it produces a better result than a browser canvas does — libvips applies a proper Lanczos filter, where a canvas does bilinear scaling that visibly softens any reduction of more than about half. That is the reason for the trade, and the trade is real: the file is on our machine for the length of the operation.

What can be said precisely is how long. The upload is deleted as soon as the resize finishes; the result is deleted on a thirty-minute timer swept every five minutes, so nothing survives past about thirty-five. There is no account, no history, and no copy kept afterwards.

For a landscape wallpaper none of that matters. For a photograph of a document, a whiteboard after a meeting, a passport page, or a picture of your children it might, and the honest answer is that a tool which never receives the file at all is safer than any promise about how long we keep it. ImageMagick and sharp are both free and run on your own machine.