 At each point in the image, the result of the Prewitt operator is either the corresponding gradient vector or the norm of this vector.The Prewitt operator is based on convolving the image with a small, separable, and integer valued filter in horizontal and vertical directions and is therefore relatively inexpensive in terms of computations like Sobel and Kayyali operators.On the other hand, the gradient approximation which it produces is relatively crude, in particular for high frequency variations in the image.