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I have seen several scales/scalebars for use in fieldwork/scientific photography that include quartered circles (similar to targets). If I understand correctly, those would be useful to correct images that were taken with the camera at an angle regarding the surface being photographed - a circle being photographed at an angle would appear as an ellipse in the final image.

Nevertheless, I've never been able to find a clear explanation of how this is done in post-processing/image editing software. Can anyone help me out with this? Many thanks!

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I assume you're talking about forensic/evidence scales. AFAIK, the circles are more to help align the camera in order to prevent oblique angles.

Generally, editing such images is not a good idea as correcting one portion could cause additional distortion elsewhere. But to correct such an image you would overlay a circle on a new layer and transform the image layer so the target circle aligned (using a program like photoshop).

The process is called rectification and involves a lot of additional steps/checks to make sure you do not create additional errors (i.e. scale comparisons, etc).

https://read.nxtbook.com/wordsmith/evidence_technology/spring_2019/angular_correction_of_forensi.html

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  • Not exclusively forensic scales, but yes, those also include such targets. I had always assumed such circles could also be used for post-processing steps but still hadn't found the best term for it - rectification. I'll look into it. Thanks! – James Jan 15 at 15:52
  • Awesome! Many, many thanks! – James Jan 15 at 19:24

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