Dashiell S R, Sawchuk A A
Appl Opt. 1977 Jul 1;16(7):1936-43. doi: 10.1364/AO.16.001936.
The halftone screen process has proven to be a useful, flexible technique for achieving general nonlinear functions in coherent optical systems. The two steps to the process involve making a binary pulse-width modulated copy of the continuous-level input using a halftone screen and spatial filtering of single diffraction orders of the image to produce the nonlinearly transformed output. The halftone screens are usually monotonic nondecreasing functions; thus the fundamental sampling periodicity of the screen is maintained. This paper describes some generalizations of the process using nonmonotonic periodic halftone screens. With this new type of screen, functions with an arbitrary number of slope changes can be obtained in the first diffraction order. A detailed synthesis algorithm for specifying the screen shape is given, along with examples and experimental realization of irradiance notch filter and quantization functions. A technique for making the halftone process more resistant to line blooming is descr bed, and a binary phase system made by bleaching ordinary halftoned input is analyzed.
半色调加网处理已被证明是一种在相干光学系统中实现一般非线性函数的有用且灵活的技术。该处理过程的两个步骤包括使用半色调网屏制作连续电平输入的二进制脉宽调制副本，以及对图像的单个衍射级进行空间滤波以产生非线性变换输出。半色调网屏通常是单调非递减函数；因此，网屏的基本采样周期得以保持。本文描述了使用非单调周期半色调网屏对该处理过程的一些推广。使用这种新型网屏，可以在一阶衍射中获得具有任意数量斜率变化的函数。给出了一种用于指定网屏形状的详细合成算法，以及辐照度陷波滤波器和量化函数的示例和实验实现。描述了一种使半色调处理更抗线条晕染的技术，并分析了通过漂白普通半色调输入制成的二元相位系统。
