CODEWITHSUNDEEP
c++opencvgeometrybackground-subtraction
Byron
Byron

Reputation: 21

Dynamic background separation and reliable circle detection with OpenCV

I am attempting to detect coloured tennis balls on a similar coloured background. I am using OpenCV and C++

This is the test image I am working with: https://i.sstatic.net/yXmO4.jpg

I have tried using multiple edge detectors; , and . All three detect the white line, but when the threshold is at a value where it can detect the edge of the tennis ball, there is too much noise in the output.

I have also tried the Hough Circle transform but as it is based on , it isn't effective.

I cannot use background subtraction because the background can move. I also cannot modify the threshold values as lighting conditions may create gradients within the tennis ball.

I feel my only option is too template match or detect the white line, however I would like to avoid this if possible.

Do you have any suggestions ?

Upvotes: 2

Views: 1267

Answers (2)

Yonatan Simson
Yonatan Simson

Reputation: 2575

What are you doing to the color image BEFORE the edge detection? Simply converting it to gray?

In my experience colorful balls pop out best when you use the HSV color space. Then you would have to decide which channel gives the best results.

Perhaps transform the image to a different feature space might be better then relying on color. Maybe try LBP which responds to texture. Then do PCA on the result to reduce the feature space to 1 single channel image and try Hough Transform on that.

Upvotes: 0

MSalters
MSalters

Reputation: 179907

I had to tilt my screen to spot the tennisball myself. It's a hard image.

That said, the default OpenCV implementation of the Hough transform uses the Canny edge detector, but it's not the only possible implementation. For these harder cases, you might need to reimplement it yourself.

You can certainly run the Hough algorithm repeatedly with different settings for the edge detection, to generate multiple candidates. Besides comparing candidates directly, you can also check that each candidate has a dominant texture (after local shading corrections) and possibly a stripe. But that might be very tricky if those tennisballs are actually captured in flight, i.e. moving.

Upvotes: 0

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