The Digital Screening Technique In The Map Publishing Visualization

The map publishing visualization is an important means of spatial data visualization. Since the map color is very important to the spatial recognition, the color rendition of map is an important issue in the map publishing visualization. The digital screening is the kernel technique of map color reproduction and color rendition. Thus, in order to enhance the effect of color reproduction in map publishing, it is very necessary to research on and apply the advanced digital screening technique. This paper thoroughly researches on the technique characteristics, arithmetic models of FM (frequency modulation) screening and AM (amplitude modulation) screening and their advantages and disadvantages. It also brings forward a new screening means, namely, FCAM (frequency conversion amplitude modulation) screening. The main researches and innovations in this paper are as follows:1. This paper analyzes and discusses the concept model of spatial data visualization, describes the relationships among the spatial data visualization, map and map publishing. It considers the map as the main product form of spatial data visualization and the publishing visualization of map as an important means of implementing spatial data visualization. It also discusses the process and principles of color transfer in map publishing system and synthetically analyzes the digital screening technique.2. It concludes many color spaces involved in map publishing system, presents the transfer relationships among the color spaces, discusses the principles of color rendering in screen dot image duplication and deduces the neugebauer equation of calculating the dot area. It also researches on the principle of Mode strips when the regular screen dot images overlap. By theoretical analysis and mathematical description of screen dot character and Morie strips, the traditional screen angles, namely, 0°, 15°, 45° and 75° in four-color printing are scientific and reasonable in theory. These four angles can reduce the effect of Morie strip to the minimum.3. Since AM screening is the mainstream in current digital screening, this paper researches thoroughly on the arithmetical model of digital AM screening technique and analyzes and compares the advantages and disadvantages of every screening algorithm. It also analyzes and researches on the principle and characteristics of FM screening technique, focusing on the arithmetical models of FM screening which include dithering arithmetic model, random and pseudo random model and dot filling model, establishes the arithmetic model of FM dot enlargement and analyzes its cause.4. Based on the analysis and evaluation of the advantages and disadvantages of current digital screening techniques, a new method of FCAM screening is brought forward independently. Through many experiments, this paper presents the basic principle and techniques of the new method, discovers and sums up some laws in the FCAM screening, and brings forward several application schemes of FCAM screening. Under the current printing technique and in virtue of the mature FM screening technique, the high fidelity color printing of four colors+ custom colors (including five colors, six colors and seven colors) can be implemented successfully by this method.5. This paper summarizes three theorems of avoiding the Morie strip in the image screening duplication. Since the screening technique was invented more than one century ago, there are two ways to avoid the Morie strip in the image screening duplication. One is FM screening in which the overlapping angles are changed, the other is AM screening. The FCAM screening brought forward in mis paper will be the third theorem of avoiding the Morie strip besides the two above-mentioned theorems.6. To meet the demands of relative projects, such as the research on the digital screening technique and the system of map publishing, the author and his colleagues in the projects develop the RIP software used for map publishing. The RIP software contains many digital screening algorithms mentioned above which can solve the problems of high quality map printing.