Prewitt operator

The Prewitt operator is used in image processing, particularly within edge detection algorithms.

Technically, it is a discrete differentiation operator, computing an approximation of the gradient of the image intensity function.

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[1] operators.

On the other hand, the gradient approximation which it produces is relatively crude, in particular for high frequency variations in the image.

At each image point, the gradient vector points in the direction of largest possible intensity increase, and the length of the gradient vector corresponds to the rate of change in that direction.

Mathematically, the operator uses two 3×3 kernels which are convolved with the original image to calculate approximations of the derivatives - one for horizontal changes, and one for vertical.