how does filter2D works in image processing for RGB image to calculate matrix output manually?

Question

I'm newbie in image processing, i have tried to implement filter2D to reduce noise image with RGB color recently, and it works well. But i don't understand how it works manually in image matrix. Anybody can help me to explain how it works manually? This is the input matrix and output matrix i get. Input Image Matrix Output Image Matrix

Thanks for your help. :)

Answer 1

as a short answer, filtering an image means apply a filter (or kernel) to it, ie; convolving the image by this kernel. For that, you take each pixel on your image and consider a neighbourhood around it. You apply the kernel to the neighbourhood by multiplying each pixel of the neighbourhood with the corresponding kernel coefficient and sum all these values. For a pixel, this can be summarized by this figure ( source ) :

For example, by setting all the coefficients to 1/N (where N is the number of elements in your kernel), you compute the average intensity of your neighbourhood. You can see https://en.wikipedia.org/wiki/Multidimensional_discrete_convolution for more information about image convolutions.

OpenCV's documentation gives some practical examples of image smoothing.

Hope it helps