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How to straighten an image?

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I tried both Distort This! and Quadrilateral Correction without much success.


Here's a method that works pretty well, but the values I used were obtained more or less by trial and error.


Run my Perspective Transformation plugin on the linked-to image with the following settings:

Upper Left:       -0.801, -1.057

Upper Right:     1.2689, -1.103

Lower Right:     0.798, 1.009

Lower Left:       -0.751, 0.857

Scale:                 1.400       

XY Proportion:  0.010

X Offset:             0.000

Y Offset:             -0.055

Antialias:            Checked


I got the values by drawing a square Shape on a transparent higher layer. I then selected the the original image layer, and moved the Perspective Transformation nodes so that the corners of the record jacket were on the corners of the square. Then I adjusted the XY Proportion to make the record circular instead of elliptical.


Another method that works okay is to make a duplicate of the image layer, and zoom in with Layers>Rotate/Zoom so that the record jacket is bigger than the original record. Run Quadrilateral Correction on the enlarged record jacket to make it square. Then switch to the original image and rerun Quadrilateral Correction, adjusting the Height and Width to produce a circular record. Enlarging the jacket in necessary because Quadrilateral Correction crops to the quadrilateral, so the quadrilateral must be large enough to contain to record.

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  • toe_head2001 changed the title to How to straighten an image?

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