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OpenCV: Computer Vision Projects with Python by Michael Beyeler, Prateek Joshi, Joseph Howse

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Custom kernels – getting convoluted

As we have just seen, many of OpenCV's predefined filters use a kernel. Remember that a kernel is a set of weights, which determine how each output pixel is calculated from a neighborhood of input pixels. Another term for a kernel is a convolution matrix. It mixes up or convolutes the pixels in a region. Similarly, a kernel-based filter may be called a convolution filter.

OpenCV provides a very versatile function, filter2D(), which applies any kernel or convolution matrix that we specify. To understand how to use this function, let's first learn the format of a convolution matrix. It is a 2D array with an odd number of rows and columns. The central element corresponds to a pixel of interest and the other elements ...

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