Several problems in the application of the phase encoding plate formed by bleaching silver halide film in image processing is described. This paper consists of four parts: 1) when the phase change of the encoding plate is limited within the definite range, the output image after bleaching is the same as before; 2) when the phase change surpasses the definite range, the pseudocolor image appears; 3) the problems of the application for pseudocolor density encoding; 4) the pseudocolor phenomenon can also appear in the other typs of tho phase encoding plate. The theoretical analysis and experimental demonstration are offered in this paper also.