Special property of complementary suppression modulated transmission (CSMT) of bacteriorhodopsin (bR) film was used to establish a new kind of optical filter,which can be used to remove incoherent bright-background in optical image. This new kind of optical filter was demonstrated and its behavior was analyzed theoretically. The calculated results showed that the quality (the contrast, the transmitted intensity and the space distribution) of the processed image was affected by the parameters (concentration and lifetime of M state) of bR film and the intensity of the bias light. With the increasing of bR film concentration, the transmitted intensity and the curvature degree of the space distribution of the transmitted intensity decreased, and the contrast increased to the maximum and then decreased to zero. By prolonging the lifetime of M state, the transmitted intensity, the curvature degree of the space distribution of the transmitted intensity increased and the contrast increased to the stable value. Accompanying the increase of the intensity of the bias light, the transmitted intensity decreased, the space distribution was not changed, and the contrast can be increased to 1. But when the concentration of bR film, the lifetime of M state and the intensity of the bias light were too large, the processed image might be distorted.