How it works
The image is drawn onto an HTML canvas at the size you choose, then exported in the format you pick. This resamples the image to the new pixel dimensions the same way a browser would when displaying it at that size.
Maintaining aspect ratio
With “maintain aspect ratio” on, changing width or height automatically scales the other dimension to match the original image’s proportions, preventing stretching or squashing. Turn it off to set an exact size regardless of the original shape.
Choosing an output format
PNG is lossless and supports transparency, making it the safest default for graphics and screenshots. JPEG is usually smaller for photos but cannot have transparency. WebP often beats both on file size at a comparable quality, with support in all current browsers.