DOCSUPRA › Crooked Scan · Español
You photographed it from above. The page still came out a trapezoid.
The short answer. Holding a phone over a page almost never puts the lens perfectly parallel to the paper. A few degrees of tilt turns a rectangle into a trapezoid — one edge longer than the other, the text leaning. Perspective correction measures the four corners and maps them back to a true rectangle. It is geometry, not guesswork, and nothing in the document changes.
It looked straight on the screen when you took it. It is only when the portal shows it back to you, or a reviewer squints at it, that the lean becomes obvious.
The 5 reasons, in plain words
- Tilt is unavoidable by hand. To be truly parallel, the phone would have to be flat above the centre of the page. Held in a hand, it is always a few degrees off — enough to see.
- The far edge shrinks. Whatever is further from the lens photographs smaller. That is why the top of the page is narrower than the bottom, and why the text size drifts down the sheet.
- Rotation and tilt are different problems. Rotating an image fixes a page that is turned. It does nothing for a page that leans away from you — that needs the four corners moved, not the whole frame spun.
- A crooked page reads as a careless one. Nothing is wrong with the document, but a leaning scan in a file of straight ones invites a second look, and a second look is what you were trying to avoid.
- Cropping makes it worse. Trimming a trapezoid to a rectangle cuts off real content at the narrow end — often a line of the form.
Which of them can software fix?
All of it, and in one pass. The four corners of the sheet are located, the page is mapped back to a true rectangle, and the edges are trimmed to the paper. Because the correction is a single resample rather than a crop, no line of the form is lost and the text stays as sharp as the original capture allowed.
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