The addition and subtraction of characters can be performed in a coherent optical processing system if a grating is used as a filter.
利用光栅作为滤波器，在相干光处理系统中可对字符进行相加和相减。
2
With a phase grating located at Fourier frequency plane, optical image subtraction is obtained as a result of the coherent superposition of the zeroth and the first order of the diffracted light.
置一位相光栅于相干光学处理系统频谱平面，利用其零级与一级衍射光的相干迭加实现图象相减。
3
An improved nearest neighbor subtraction algorithm was presented and applied in the Computational Optical Section Microscopy (COSM).