6.1- Introduction
6.2 -Gradient Based Edge Detection
        6.2.1 Roberts
        6.2.2 Sobel
        6.2.3 Prewitt

6.3 - Laplacian Based Edge Detection
6.4 - Canny’s Edge Detection

6.2.1 ROBERTS          

  The Roberts cross operator provides a simple approximation to the gradient magnitude:

 

Using convolution masks, this becomes:
 

 

where Gx and Gy are calculated using the following masks:
 

 

    As with the previous 2 x 2 gradient operator, the differences are computed at the interpolated point [i + 1/2, j + 1/2]. The Roberts operator is an approximation to the continuous gradient at this interpolated point and not at the point [i, j] as might be expected.

Click here For The Gradient Based Edge Detection Applet