Convolution involving turning each pixel value to the most represented pixel value of the neighbourhood

Question

In order to correct gradual changes of intensities in the background of grey-scales images, I have been blurring them and then subtracting the original images from the convolved one.

In some cases, I have seen improvement using median blur instead of blur.

I was therefore wondering if I could go further and use a filter that convolves a grey-scale image so that each pixel will take the value of the most represented pixel value in the histogram of a rectangular neighbourhood.

Do you know the name of this convolution ?

Are you aware of any implementation in OpenCV ?

Thank you very much,

Answer 1

This is a non-linear filter, the operation being performed is not a convolution and cannot be represented by a filter kernel. It is sometimes called a mode filter, by analogy to the median filter, since the value taken by a pixel is the mode of the distribution of the neighboring values. OpenCV does median filtering (cvSmooth with CV_MEDIAN parameter), I don't think it does mode filtering though.