 This implies that the result of the Prewitt operator at an image point which is in a region of constant image intensity is a zero vector and at a point on an edge is a vector which points across the edge, from darker to brighter values.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.If we define formula_1 as the source image, and formula_2 and formula_3 are two images which at each point contain the horizontal and vertical derivative approximations, the latter are computed as