CODEWITHSUNDEEP
camerageometrycomputer-vision
Valeriy
Valeriy

Reputation: 805

Perspective distortions correction

I'm searching for a methods of text recognition based on document borders. Or the methods that can solve the problem of finding new viewpoint. For exmp. the camera is in point (x1,y1,z1) and the result picture with perspective distortions, but we can find (x2,y2,z2) for camera to correct picture.

Thanks.

Upvotes: 1

Views: 268

Answers (1)

Francesco Callari
Francesco Callari

Reputation: 11785

The usual approach, which assumes that the document's page is approximately flat in 3D space, is to warp the quadrangle encompassing the page into a rectangle. To do so you must estimate a homography, i.e. a (linear) projective transformation between the original image and its warped counterpart.

The estimation requires matching points (or lines) between the two images, and a common choice for documents is to map the page corners in the original images to the image corners of the warped image. This will in general produce a rectangle with an incorrect aspect ratio (i.e. the warped page will look "wider" or "taller" than the real one), but this can be easily corrected if you happen to know in advance what the real aspect ratio is (for example, because you know the type of paper used, whether letter, A4, etc.).

A simple algorithm to perform the estimation is the so-called Direct Linear Transformation.

The OpenCV library contains routines to help accomplishing all these tasks, look into it.

Upvotes: 2

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