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!


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).


| improve this answer | |
  • 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

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.