How content-aware scaling works
A seam is a connected path of one pixel per row (or column). The engine scores every possible seam by how much new edge its removal would create (“forward energy”), removes the cheapest, and repeats. To widen a picture it finds the cheapest seams and duplicates them instead, a batch at a time so no seam is stretched twice.
Paint over a face or a product with the Protect brush and seams route around it. Paint over something unwanted with Remove and seams go through it first. Turn on “Show seams” afterwards to see exactly which pixels were taken out or doubled.
When to use it — and when not
It shines on pictures with calm areas: landscapes, skies, studio backgrounds, walls. It struggles when the whole frame is busy or full of straight lines across the direction of change. Compare with Pad or Fill & crop in Resize image pixels, and keep whichever looks right.
Seams are computed on a copy of up to 1 megapixel, which keeps the job to seconds; larger pictures are reduced first, and you can scale the result back up to full size with Lanczos-3 in the same step.
Questions
Can I change aspect ratio without cropping?
Yes: content-aware scaling changes the shape by removing or adding low-detail seams. Pad mode in Resize image pixels is the other no-crop option, adding bars instead.
Will it distort faces?
It can if a face sits where the cheapest seams run. Paint the face with the Protect brush before scaling.
How much can I change the shape?
Removing up to about a third of a side usually looks natural on calm pictures. Beyond that, or on busy pictures, expect visible bending.
Is my picture uploaded anywhere?
No. Decoding, scaling and encoding all run in this browser tab, and the scaling engine runs in a Web Worker with no network code in it. The only download the site can make for you is an AI model file, and only after you press the button that names its size — that request contains no picture.