General morphological correlation (GMC) is proposed and hardware design for a compact joint transform correlator(JTC) is proposed in order to implement GMC. Two kinds of modified general morphological correlation is studied. The gray-scale image is decomposed into a set of binary image slices in certain decomposition method. In the first algorithm,the edge of each binary joint image slice is detected and the joint power spectrum of which is summed. In the second algorithm,one situation is that the joint power spectrum of each pair is binarized or thinned and then summed,and another situation is that the summation of the joint power spectrums of these pairs is binarized or thinned. Computer-simulation results indicate that the modified algorithm can improve the discrimination capabilities with respect to the high similarity gray-scale face images.