Matlab's Conv2 equivalent in OpenCV

Question

I have been trying to do Convolution of a 2D Matrix using OpenCV. I actually went through this code http://blog.timmlinder.com/2011/07/opencv-equivalent-to-matlabs-conv2-fun

Answer 1

If you want an exclusive OpenCV solution, use cv2.filter2D function. But you should adjust the borderType flag if you want to get the correct output as that of matlab.

>>> A = np.array([ [1,-2],[3,4] ]).astype('float32')
>>> A
array([[ 1., -2.],
       [ 3.,  4.]], dtype=float32)

>>> B = np.array([[ 0.707,-0.707]])
>>> B
array([[ 0.707, -0.707]])

>>> cv2.filter2D(A2,-1,B,borderType = cv2.BORDER_CONSTANT)
array([[-0.70700002,  2.12100005, -1.41400003],
       [-2.12100005, -0.70700002,  2.82800007]], dtype=float32)

borderType is important. To find the convolution you need values outside the array. If you want to get matlab like output, you need to pass cv2.BORDER_CONSTANT. See output is greater in size than input.