调幅网加网因子研究

Research of Screening Factor in Amplitude Modulation Screening

调幅式数字加网,由于各分色版的网点具有不同的网线角度,在确定原稿图像扫描输入分辨率时通常要乘以1.5～2.0的加网因子,这在业界已成定式。本文依据调幅网加网过程的原理分析和实验结果,查明加网因子源自RIP加网时原灰度图像的4个像素对应于加网图像的1个网格,与网线角度无关。采用加网因子可保留原图像较多的空间细节,提高加网图像的清晰度,并明确指出调幅网的加网因子应等于2。

Most researchers of printing industry believed that the scanning resolution should be multiplied by screening factor which was a rational number from 1.5 to 2.0, when original images were digitized. The main reason was that processing of color separation has four different screen angles. Based on the principle of AM screening and the analysis of experiments, the relationship was not observed between the screening factor and the screen angles. The real reason of using it was that four pixels in the original gray image correspond a halftone unit of the screening image. The research concludes that the screening factor enable to maintain more space detail of the original image, and to enhance the definition. Furthermore, the screening factor in AM screening should be 2.