Can calcBackProject be used with HOG?

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Hello,

I have used calcBackProject() with color histograms to successfully locate a target patch within an image. I was wondering if I can do something similar using gradient histograms instead of color? From the digits.py example I see how I can construct gradient histograms from Sobel edge filters. But is there a way I can now plug these into the calcBackProject() function to locate a target in an image?

Thanks!
patrick