The distorted (scale and rotation etc.) target images and the training images are edge extracted by Prewitt operator. The Maximum Average Correlation Height filter is synthesized with the training images. The low frequency information of the distorted target images and the filter is enhanced. Then the edge extracted distorted target image is filtered by the Maximum Average correlation Height filter. Thereby, the distortion tolerance of the Maximum Average Correlation Height filter is expanded. By this method, when the space edge extraction combines with frequency domain filtering, the scale distortion tolerance is 0.76~1.56 times; the rotation distortion tolerance can reach up to 80 degrees. For the targets exceeding the distortion tolerance range, the intensity of correlation peak becomes weaker and weaker, but some of the targets can still be identified.
