CODEWITHSUNDEEP
opencvcomputer-vision
JoeyCK
JoeyCK

Reputation: 1402

How can I transform an image to match a circular model in OpenCV

I'm trying to make a program that can take an image of a dartboard and read the score. So far I can get the position of each dart by comparing it to a model image as you can see here:

enter image description here

However this only works if the input image is practically the same. In this other case the board is slightly in a different perspective so I was thinking maybe I can transform the image to match the model image and then do the process that you can see above.

enter image description here

So my question is: How can I transform this last image to match the shape and pespective of the model dart board with OpenCV?

Upvotes: 0

Views: 519

Answers (2)

hiroki
hiroki

Reputation: 401

I don't think comparing an image with the model that was captured using a different subject with a different angle is a good idea. There should be lots of small differences even after perfectly matching them geometrically - like shades, lighting, color differences, etc.

I would just capture an image every time the game begin (reference) and extract the features (straight lines seem good enough) and then after the game, capture an image, subtract the reference, and do blob analysis to find darts.

Upvotes: 0

gfkri
gfkri

Reputation: 2179

The dart board is basically planar. Thus, you can model the wanted transformation by a homography. Now you can perform a simple feature extraction and matching like here or if speed is not as important utilize an intensity based parametric alignment algorithm (more accurate).

However, as already mentioned in the comments, it will not be as simple afterwards. The dart flights will (depending on the distortion) most likely cover an area of your board which does not coincide with the actual score. Actually, even with a frontal view it is difficult to say.

I assume you will have to find the point on which the darts stick in your board. Furthermore, I think this will be easier with a view from a certain angle. Maybe, you can fit lines segments just in the area where you detected a difference beforehand.

Upvotes: 1

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