According to the shortcoming of the classical gradient operator

this paper gives an improved computational formula for edge direction. The edge direction of the classical gradient operator is given by an anti-tangent function

and the angle range which the anti-tangent function can represent is [-π/2

π/2]

but the range of edge direction is [0

2π]. This paper analyzes the operator from the gradient operators

and points out that the classical gradient operator can not discrete two edges which have a difference ofπin edge direction

and gives a improved computational formula for edge direction. In the classical gradient operator

because the computational formula for edge direction is not precise

the following image edge thinning

short edge removing

aperture filling and edge linking are constructed on a non-precision foundation

error results being got. Because of the error in low-level image processing

the quality of following high-level image processing is low. The computer-simulated experiments show that

the improved computational formula of edge direction in this paper is correct and effective.