Resizing images in your browser: faster and safer

A server-based resizer has to receive your whole file before it can do anything. Then it processes the image and sends a new file back. That means two transfers over your connection, and a copy of your image sitting on someone else’s machine for however long their retention policy allows.

Modern browsers can do the work themselves. The browser decodes your image into memory, draws it onto a canvas at the new dimensions, and then encodes the canvas as a JPG, PNG or WebP file. The result is handed to you as a normal download. Every step happens on your device, using the Canvas API and image bitmaps that browsers already include.

There is no upload and no download of the result, so the time it takes depends on your device rather than your connection. That matters most on slow or metered mobile data and when you are processing a batch: Bulk Resize handles up to 30 images in one go without sending any of them anywhere.

If the file never leaves your device, there is no copy to delete, no server to be breached and no account to create. That is useful for photos of documents, IDs, medical forms and anything else you would rather not hand to a third party. Re-encoding through a canvas also normally removes embedded metadata such as camera details and location tags.

You don’t have to take any website’s word for it. Your browser can show you what is being sent:

In-browser processing depends on your device. Very large images use a lot of memory, which is why each file is limited to 50 MB. Which formats can be opened also depends on the browser: HEIC photos, for example, are only readable where the browser or operating system can decode them. If a file can’t be read, the tool tells you rather than failing silently.