How to detect black edges only using sobel or matched filter?

I have an image with different kind of edges. But I want to detect the edges of black color. I have intended to so by using convolution. I need suggestions for the kernel filter.

Answer 1

[Kushagr Gupta]

In order to perform edge detection for black edges, it would be best to invert the values of the image such that the black pixels become white and vice-versa. Perform the filtering on the inverted image in order to see the edges. If need be, it can again be inverted to convert the edges back to black.

This way, you would not have to worry about the coefficients of the filters that are needed for the convolution operation.