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1、 摘 要 数字半色调技术的研究摘 要 数字半色调技术的研究 本文主要研究了数字半色调技术,分析、实现并对比了误差扩散算法、有序抖动算法和点扩散算法,对它们三种算法的结果进行优劣比较。对三种算法都做了改动,将原来的误差扩散的逐行扫描修改为 S 型的扫描;有序抖动算法进行了改进,改善了半色调图像的显示效果,对于点扩散算法在不改变显示效果的前提下,提高算法的执行效率。 数字半色调技术是利用人眼视觉的一些特性,在数学、计算机等工具的帮助下,将一幅连续图像转换成二值图像的一门技术。人眼在看图像时,是将在空间上几个相互接近的几个或更多的点看成一个整体而取平均。利用这个特性,我们在观察用半色调处理过的图像时
2、,对某一图像的局部的平均灰度等级接近于该图像原始连续图像的灰度等级,使该半色调图像在整体上形成连续的效果。 误差扩散算法是一种应用广泛且处理效果较好的半色调算法。这种算法主要是对邻域的处理,在不引起网点增大的情况下它能够为印刷机提供更高的半色调质量,而且生成的半色调图像灰度等级丰富,各像素点同时具有各向异性。其方法可以理解为先按照规定的扫描路径 (路径可以是逐行也可以自定义) 进行阈值量化该图像的像素,然后将量化后所得的误差以某种特定的方式扩散到与其相邻的且未被处理的像素上。 点扩散技术是两者的合二为一,它同时兼有两者的优点,所以它处理后的图像即不会像误差扩散算法处理后的图像带有龟纹,也不会像
3、有序抖动算法那样使人感觉图像特别生硬。该方法是首先对亮度等级为 1 的像素进行定位,然后与所选的抖动矩阵进行对比,所得的误差再用误差扩散算法进行处理,这一结果比有序抖动方法处理后的图像更加清晰,但是有时也会产生源图像所没有的特征。在实际应用中,点扩散算法在打印图像时的效果也明显好于误差扩散算法和有序拉动。 关键词:关键词: 误差扩散算法, 有序抖动算法, 点扩散算法, 数字半色调技术 Abstract Abstract The Research on Digital Halftone This paper mainly investigates digital halftone algorit
4、hm including error diffusion algorithm, ordered dither algorithm and dot diffusion algorithm. The performance of three algorithms is compared and analyzed. The improvement of ordered dither algorithm makes it different with the result of the original algorithm. Digital halftone technology uses some
5、features of the human vision, and converts a continuous image into a binary image with the tools such as mathematics and computer. When looking at an image, human eyes will take a few or more close points as a whole and take the average. Using this feature, when we observe a halftone image, an avera
6、ge gray level in a particular local area is close to the gray level of the corresponding original continuous image, and forms a continuous effect on the whole. Error Diffusion algorithm is a widely used algorithm with better results. This algorithm is mainly used for neighborhood processing. Under t
7、he condition of avoid increasing point size, it can provide higher quality for printing, and the generated halftone images have rich gray levels, each pixels in the halftone images are anisotropic. The method can be implemented by thresholding the image pixels according to the predefined scan path (
8、scan path can be line by line or can be customized), the obtained error after thersholding is spread to nonprocessed pixels in the neighborhood in some specific ways. Dot diffusion technology incorporates the two algorithms, and has the merits of both at the same time, so the processed image using d
9、ot diffusion doesnt have artifacts as error diffusion algorithm does, and doesnt makes people feel image special curt as ordered dither algorithm does. The produced results using dot diffusion is clearer than the results using ordered dither algorithm. In practical applications, the printing effect
10、using dot diffusion algorithm is significantly better than error diffusion algorithm and ordered dither algorithm. Keywords: Keywords: Error Diffusion algorithm, ordered dither algorithm, Dot diffusion algorithm, Digital Halftones 目 录 摘 要ABSTRACT第 1 章 绪 论.1 1.1 数字半色调技术 .1 1.2 数字半色调技术的分类 .1 1.3 数字半色调
11、技术的发展 .2 第 2 章 MATLAB 程序设计 .3 2.1 MATLAB 简介.3 2.2 特 点.3 2.3 算法相关函数介绍 .4 第 3 章 半色调技术.5 3.1 半色调技术中图像的显示 .5 3.2 规定抖动矩阵的规则 .6 3.3 高等级模板的结构 .7 3.4 误差扩散的基本思想 .8 3.5 有序抖动的基本思想 .9 3.6 点扩散算法的基本思想 .10 3.7 边界的加强 .11 第 4 章 误差扩散、有序抖动和点扩散的实现.12 4.1 误差扩散算法的实现 .12 4.1.1 误差扩散算法的 MATLAB 代码.12 4.1.2 对程序的解释 .13 4.1.3 误差扩散算法的结果分析 .14 4.2 有序抖动算法的实现 .14 4.2.1 有序抖动算法的 MATLAB 代码.14 4.2.2 有序抖动算法的解释.15 4.2.3 有序抖动算法的结果.16 4.3 点扩散算法的实现 .17 4.3.1 点扩散算法的 MATLAB 代码.17 4.3.2 点扩散算法的解释.18 4.3.3 点扩散算法的结果.20 4.4 对误差扩散的改进 .20 4.4.1 误差是固定值.20 4.4.2 边界的加强.