How it works
Marking the corners
Drag each of the four corners onto a corner of the page, sign or screen. Drag an edge or the middle to move more than one corner at once, or use the arrow keys on a focused corner. The outline must stay a four-sided shape; if corners cross, the tool asks you to drag them back.
How it is straightened
The four corners define a perspective transform that maps your outline onto a rectangle. Its width and height come from the longer of each pair of opposite sides, so a page keeps about the size it has in the photo.
Aspect can stay Auto or be set to A4, Letter, 1:1, 4:3, 3:2, 16:9 or a custom ratio, which adjusts the shorter side. The straightened picture is saved as a PNG.
