分析了联合傅里叶变换相关器存在较强的零级衍射且宽度很大，限制了输入图像的大小和相对位置的问题.提出了将参考图像和待识别图像分别置于马赫—曾德干涉仪的两臂，并将实时采集到的联合功率谱与事先存储的待识别和目标图像的功率谱进行相减的方法.改进方法可使原两个相关输出项移到坐标中心，既提高了识别能力，也增大了输入图像的尺寸.

The Joint Fourier Transform Correlator (JTC) exists a strong and widely zero-order diffraction, which restricts the input image size and its relative position. A method is presented to place respectively the reference image and the image to be identified in the arms of Mach-Zehnder interferometer, and to make the joint power spectrum and the identified targets power spectrum subtraction. The improving method can make two original outpour items move to eh coordinate center, it not only improves the ability of identification, but also increases the input image size.