Using the coca cola logo as the calibration pattern for camera

Question

I am looking for camera calibration techniques with OpenCV and saw the chessboard and circles methods, but I wanted to calibrate the camera with something that is in the real world and you don't have to print (printers are also not very accurate in what they print).

Is it possible to do calibration with complex shapes like the Coca Cola logo on the cans? Is it a problem that the surface is curved?

Thanks

Answer 1

Depending on what you want to achieve this is not at all necessarily a bad idea, and you are not the first one who had it. There was a technology that uses a CD, which is a strongly standardised object which at least used to exist on most households, for a simple camera calibration task. (There is little technical to be found online about this, as the technology was proprietary. This is business document, where the use of the CD is mentioned. Algorithmically, however, it is not difficult if you know camera calibration.)

The question is whether the precision you get is sufficient for your application. Don't expect any miracles here. Generally you can use almost any object you like to learn something about a camera, as long as you can detect it reliably and you know its geometry. Almost certainly you will have to take several pictures of the object. Curved surfaces are no problem per see. I regularly used a cylinder (larger than a beverage can, though, with a simple to detect pattern) to calibrate a complete camera rig of 12 SLRs.

Don't expect to find out of the box solutions and don't expect implementation to be trivial. You will have to work your way through the math. I recommend the book by Hartley and Zisserman, Multiple View Geometry for Computer vision. This paper describes an analysis-by-synthesis approach to calibration, which is the way to go for here (it does not describe exactly what you want, but the approach should generalise to arbitrary objects as long as you can detect them).

Answer 2

i can understand your wish, but it's a bad idea.

the calibration algorithm works by comparing real world points from the cam with a synthetical model ( yes, you have to supply that , too! ). so, while it's easy to calculate a 2d chessboard grid on the fly and use that, it will be very hard to do for your tin can, or any arbitrary household item you grab.

just give in, and print a rectangular chessbord grid to a piece of paper

(opencv comes with a pdf for that already).

don't use a real-life chessboard, a quadratic one is ambiguous to 90° rotation.

Answer 3

interesting idea.

What about displaying a checkerboard pattern (or sth else) on an lcd screen display and use that display as calibration pattern?? You would have to know the displaying size of the pattern though. Googling I found this paper:

CAMERA CALIBRATION BASED ON LIQUID CRYSTAL DISPLAY (LCD) ZHAN Zongqian http://www.isprs.org/proceedings/XXXVII/congress/3b_pdf/04.pdf

comment: this doesn't answer the question about the coca-cola can but gives and idea for a solution to the grounding problem: camera calibration with a common object.