Abstract: Image information entropy and gray modification average value arc two familiar image encryption effect evaluation criterions. We pointed out that these two criterions are influenced obviously by the size of images,and two new image encryption effect evaluation criterions were presented,that is,histogram proportion degree and run statistic. Histogram proportion degree can be used in the effect evaluation of image encryption algorithm based on the image pixel gray values modification, and run statistic can be used in the effect evaluating of image encryption algorithm based on the image pixel coordinate permutation. The proposed criterions arc simple on expression and convenient in computation, their main advantages arc having litter effect on the size of images and the computing process arc only related with the encrypted image.

Key words: Image encryption, Image information entropy, Gray modification average value, Evaluation criterion