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I have a project that requires that picture frames and similar objects in an image taken from a smartphone app be measured. The smartphone will likely be able to provide some angle & orientation data.

Is this possible to do within a quarter of an inch with openCV?

Examples would be very helpful, someone that wants cash for an mvp would be outstanding

Robert Speer
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  • Start by detecting squares/rectangles: http://stackoverflow.com/questions/8667818/opencv-c-obj-c-detecting-a-sheet-of-paper-square-detection – Dan Dec 03 '14 at 18:18

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No can do from a single image, without additional information. Absolute scale is lost in projection. A good survey of what is possible/not possible from single image is this paper.

Francesco Callari
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  • Fascinating. I am considering multiple pictures at different angles, and/or a orientation graphic printed on a standard piece of printer paper. Would either of those make this doable? – Robert Speer Dec 04 '14 at 19:56
  • Yes. If a "standard" object of known size is visible and it is on the same plane as the object to be measured, then one image is enough and scale can be trivially recovered. The paper I mentioned extends this idea to cases in which parallel planes can be identified. If you go to multiple images / multiview reconstruction you can relax some constraints, but you will still need either a scale reference or a calibrated camera setup to recover size with any accuracy. – Francesco Callari Dec 04 '14 at 21:47