How can we use the colormatrix only a part of image rather than whole image?

Question

I know the use of colormatrix. but this work on the whole image. is there any way to work with colormatrix only a part of image rather than whole image.

eg i want to give the brightness of only border area of image.

i am working with c#.

Answer 1

Given that a ColorMatrix only works on individual colour vectors/pixels, "all" you need to do is choose your pixels carefully so that they match your criteria.

It's been a while, but if you scan the pixels row by row then the whole of the first and last n rows and the first and last n columns of all the other rows can be transformed.