Electrical and Computer Engineering Department, University of Rochester, Rochester, NY 14627-0126, USA.
IEEE Trans Image Process. 2009 Dec;18(12):2718-34. doi: 10.1109/TIP.2009.2028367. Epub 2009 Jul 24.
A generalization of periodic clustered-dot halftones is proposed, wherein the phase of the halftone spots is modulated using a secondary signal. The process is accomplished by using an analytic halftone threshold function that allows halftones to be generated with controlled phase variation in different regions of the printed page. The method can also be used to modulate the screen frequency, albeit with additional constraints. Visible artifacts are minimized/eliminated by ensuring the continuity of the modulation in phase. Limitations and capabilities of the method are analyzed through a quantitative model. The technique can be exploited for two applications that are presented in this paper: a) embedding watermarks in the halftone image by encoding information in phase or in frequency and b) modulating the screen frequency according to the frequency content of the continuous tone image in order to improve spatial and tonal rendering. Experimental performance is demonstrated for both applications.
提出了一种周期性聚类点半色调的推广，其中使用二次信号调制半色调点的相位。该过程通过使用解析半色调阈值函数来完成，该函数允许在打印页面的不同区域生成具有受控相位变化的半色调。该方法还可用于调制屏幕频率，但存在额外的限制。通过确保调制相位的连续性，最小化/消除可见伪影。通过定量模型分析该方法的局限性和能力。该技术可用于本文介绍的两种应用：a）通过在相位或频率中编码信息将水印嵌入半色调图像中，b）根据连续色调图像的频率内容调制屏幕频率，以改善空间和色调渲染。对这两种应用都进行了实验性能验证。
