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I wonder can anyone give me some recommendations on image-adjustment programmes for a PC which can correct the perspective distances in a scanned photograph?

 

I am doing a lot of drawing from photographs and have used GIMP to correct the converging horizontals and verticals in the photos, but that program has no facility (as far as I know) to correct the gradual compression of scale away from the centre of a photograph. Can anyone recommend an alternative program which has this facility please?

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gimp can do forward and reverse perspective correction as standard. See the gimp book or ask google for "gimp reverse perspective correction" for some tutorials.

 

The real nasty evil horror here that most people don't understand though is that if you correct the perspective for one depth of an image it is wrong for every other depth. So if you correct a van for example to be flat on chances are the doors are now not quite in the right place. Sometimes you can do two corrections (eg for outside framing) other times you just have to guess.

 

At least you can build your 3D model for printing and put it in a scene to compare with the photograph at the same angles.

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Pixels,

Thanks, but for the record GIMP cannot correct the distance distortion of perspective. One superimposes a rectangular grid onto the photograph and moves the corners to form a trapezium which follows the converging lines which should be horizontal or vertical. So far so good. However the elements of the original grid in GIMP are all the same size, instead of reducing gradually towards the convergence points. To quote the manual for GIMP 2.8, Section 4.8 Perspective: “ This tool is not actually a perspective tool, as it doesn't impose perspective rules. It is better described as a distort tool.”

Considering the classic train photo from a ¾ angle with the locomotive at the front and the train gradually receding into the distance. The apparent length of the coaches reduces drastically towards the rear of the train and this needs a gradually reducing grid to support distance correction. Does anyone have any suggestions please?

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It is not mathematically possible to do true correction of an object with multiple depths. There is not sufficient information in the image to do this. Hence my warning about depths.

 

Note also you need the *reverse perspective* tool not the perspective tool.

 

See the tutorial at: http://www.templot.com/martweb/info_files/gimp_example.htm

 

which is a worked example of rescaling a van in order to measure it up.

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