Error Concealment | JPEG | MPEG-4 | Wavelet | YUV

Hi,

        I am learing Image processing. I want to do an edge detection
programme without using the masks (sobel, canny,robert..). So the
point is, given a image, find the gradient and apply the threshold.

       I have struck up in very first step that is finding a gradient
for image matrix(2d). 

        Please tell me the ideas how to find gradient of a image.

thanks in advance.
Pradeep

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