Learning OpenCV 4 Computer Vision with Python 3 - Third Edition

HPFs and LPFs

An HPF is a filter that examines a region of an image and boosts the intensity of certain pixels based on the difference in the intensity of the surrounding pixels.

Take, for example, the following kernel:

[[ 0,    -0.25,  0   ],[-0.25,  1,    -0.25],[ 0,    -0.25,  0   ]]

A kernel is a set of weights that are applied to a region in a source image to generate a single pixel in the destination image. For example, if we call an OpenCV function with a parameter to specify a kernel size or ksize of 7, this implies that 49 (7 x 7) source pixels are considered when generating each destination pixel. We can think of a kernel as a piece of frosted glass moving over the source image and letting a diffused blend of the source's light pass through.