The following functions are used to detect edges in an image by convolving various kernels in sequence over the image matrix. Edge detection is used to enhance image readability for certain types of features that depend on boundaries.
• freichen(M)—Performs edge detection by Frei-Chen convolution on matrix M.
• prewitt(M)—Performs edge detection by Prewitt convolution on matrix M.
• roberts(M)—Performs edge detection by Roberts convolution on matrix M.
• sobel(M)—Performs edge detection by Sobel convolution on matrix M.
The functions return a matrix containing the detected edges. The perimeter of the image is untreated, since the kernels do not fully overlap there.