HOGDescriptor window size adjustment adjustment

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I am using HOGDescriptor::compute to get the HOG feature descriptor in the input image, but my input image if of size 80x64 of which HOG feature descriptor is required. AS default window size of HOGDescriptor is 64x128 so the program end with exception. that is why i need to change the default window size of HOGDescriptor equal to input image to avoid the exception. i read HOG documentation at [http://docs.opencv.org/3.1.0/d5/d33/s...] but don't understand.. if possible kindly help me