Deskew

Deskew straightens a photograph of a document by undoing the perspective: you drag four handles onto the corners of the page and get a flat rectangle back. A page shot from an angle is a trapezoid rather than a parallelogram, which is more than a canvas transform can express, so the tool solves an eight-unknown homography from the corners you place and samples every output pixel back through the inverse of it, bilinearly. The output shape can follow the quad you drew, or lock to A4, Letter or square.

How it works

  1. Drop one photo of a document Deskew works on one image at a time. Drop several and the first one is kept.
  2. Drag the four handles onto the page corners They start inset from the edges of the image, clockwise from the top left. Once a handle has focus the arrow keys move it a pixel at a time and shift moves it ten.
  3. Choose the output shape Auto reads the size back from the quad you drew — the average of its two widths and the average of its two heights. A4, Letter and Square fix the ratio instead and the size follows the long edge.
  4. Adjust the output size if you want The width and height fields are prefilled from the quad. Type over them and corner drags stop resizing the output.
  5. Export the straightened page Pick a format and, for lossy formats, a quality, then export. The flattened rectangle is written from the canvas at the size you set.

Questions

Does deskew crop away everything outside the four corners?
The four corners you place are mapped onto the corners of a rectangle and every output pixel is sampled back through that map. Nothing is cut out as such — whatever lies outside the quad is simply never sampled, so it does not appear in the result.
Does it find the page for me?
No. There is no page detection: you place the four corners yourself, and it handles one image at a time rather than a batch. The corners also have to form a convex quad — four points that fold over each other, or that sit close to a straight line, describe no page shape, and the tool says so rather than producing something wrong.
Does the exported file keep the camera's EXIF data?
No. Exporting writes a new file from the canvas, so the camera model, the timestamp and any location tag in the original are not carried over.

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