中文摘要：

数字半色调又称数字加网,它实现了连续调图像到半色调图像的转变.频率调制（FM）半色调是数字半色调技术中继幅度调制半色调之后出现的另一种技术.调频网点数量大且尺寸微小难以控制,网点容易丢失导致图像阶调损失.同时,远超过调幅加网的网点总周长直接造成网点的严重扩大变形,致使数字图像还原存在较大色偏.为有效控制网点扩大,真实再现数字原稿图像,提出了一种高阶网点集聚型重心定位频率调制半色调算法.首先对重心定位进行建模分析,确定用于随机数选取的发生器,并建立组合随机数组筛选模型以选取网点重心.根据网点重心和灰度级分配方案,具体构建了生成高阶网点集聚的算法模型.针对存在的问题,确定了重心取舍和压盖关系处理模型,最后通过实验对算法做出评价.实验表明,该算法能够生成高阶网点集聚的半色调图像,在网点统计数据等多项指标上均优于传统算法,能够有效控制网点周长和扩大,真实再现原稿图像.

英文摘要：

Digital halftoning is also called screening.It realizes the transformation from continuous tone image to halftone image.FM halftoning is a new technique after AM screening in digital halftoning technology.The quantity of FM screening dots is large while they are hard to be controlled.Usually,they will be easily lost to cause image tone missing.Meanwhile,the total dot perimeter of FM halftoning far exceeds AM halftoning,which directly causes severe dot gain and more color cast.In order to control dot gain and reproduce digital image,this paper brings forward a FM halftoning algorithm of high-order dot gathering based on dot center location.Firstly,the idea is modeled and analyzed.Then pseudo random generator is confirmed and selecting model is set up to select combined pseudo random numbers to confirm dot centers.According to grey level distribution,dot generating algorithm model is set up.Aiming at existing problems,dot center accept or reject model and dot cover relationship model are set up.Finally,ex-periments are performed and testify that this algorithm can generate halftone image with high-order dot gathering.In many index such as dot statistics data,etc,this algorithm is better than traditional ones,which can effectively control dot perimeter and dot gain as well as accurately reappear manuscript image.