A digital image is a numeric representation of (normally binary) a two-dimensional image. Depending on whether the image resolution is fixed, it may be of vector or raster type, by itself, the term ¿digital image¿ usually refers to raster images or bit mapped images. As the Sobel edge detection is approximation of the gradient of the image intensity a very common first order edge detection operator which computes an function. At each part in the image the result of the Sobel operator is the corresponding norm of this gradient vector. The Sobel operator only considers the two orientations which are 0°and 90°convolution and there must be more work on, more than two convolution kernels to detect the edge of image so that higher accuracy can be gained.