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The color desktop publishing system is also called the DTP system. Its task is to perform various processing on the images, text, and graphic information that need to be copied and to make a film or a printing plate.
The color desktop publishing system is a rapid and effective plate making device mainly composed of a computer, which is mainly composed of a scanner (or an extension front end), a computer, and an image forming machine. The color separation platemaking is basically divided into three parts: graphic information input, graphic information processing and graphic information output. Here mainly introduces the input of graphic information, namely color separation technology.
The collection of graphic and textual information mainly has two methods: one is an electronic method, such as the use of a digital camera or a camera for taking manuscripts. In the past, due to the low precision of these devices, the manuscripts were rarely used in the printing of manuscripts, but in recent years, there have been few applications. Due to the continuous improvement of these devices, more and more applications have been made in the field of plate separation; the other method is the mechanical scanning method, including drum scanning and flat panel scanning.
Flat-panel scanners use CCDs as photoelectric conversion devices. They are not as good as the drum scanners that use photomultiplier tubes as photoelectric conversion devices in sampling accuracy, resolution, gradation range, and dark tone details. Although the high-end professional flatbed scanner has a certain gap with the drum scanner, it has now developed to a very high level and the price is much cheaper than the drum scanner. It can be used for scanning production of many high-end products and is now widely used.
Due to the high accuracy of the sampling and the wide range of tone adjustments, the roller scanning method can display a rich level of darkness, which is an indispensable device for high-grade original scanning.
2 The basic principle of separation
Using the principles of color science, we know that all colors can be formed by combining the three primary colors yellow, magenta, and cyan of pigments in different proportions. That is to say, in principle, any color can be reproduced with the ideal three-primary color materials, but the actual production The color reproduction capabilities of these three primary color inks are limited, and therefore, there are always some errors in the color reproduction of some manuscripts, such as purer blue-violet colors, which are difficult to reproduce completely.
Colors can be divided into two categories, colored and non-colored. Achromatic, also known as achromatic, refers to white, black, and shades of gray. They form a series, from white to light gray, medium gray, and then dark gray until Black, called black and white series. Color refers to a variety of colors other than the black and white series, even red, there are light red, dark red and bright points. In order to analyze and distinguish the various colors correctly, the world has unifiedly defined the three attributes of color discrimination: hue, lightness, and saturation. Hue, also known as hue, is the physical quantity of a color feature. It is used to identify different colors. Each hue has a corresponding wavelength, which is a feature that distinguishes colors from each other. Brightness, also known as brightness, distinguishes the difference between bright and dark in the same color. Saturation, also known as chroma, refers to the purity or vividness of color, and the saturation of each monochromatic light in the visible spectrum is the highest. There is only a difference in brightness for achromatism, and there is no hue and saturation. For each color, it has these three attributes. Therefore, it is extremely important to correctly grasp these three attributes in color separation.
The color image is printed and overprinted with yellow (Y), magenta (M), cyan (C), and black (K) four-color inks. Therefore, the color image needs to be decomposed by color, that is, the original is colorful. The color is decomposed into four colors of C, M, Y, and K to obtain the four-color printing plate. Such a process is called color separation. What the platemaking does is the decomposition of the color, what the printing does is the synthesis of the color, the conversion in the middle is the transmission of the color. To get the perfect print, first of all, to separate the technology of good separation, so color separation is a crucial process in the reproduction of the entire manuscript.
The purpose of an electric extension or a roller scanner as a scanning input system is to decompose continuous colors on a manuscript into color separation information through a color filter, and to form discrete dot matrix images by scanning heads so that information on each point on the manuscript After scanning and sampling, it is decomposed into color information for each point of space coordinates, and these colors are corrected and processed.
The principle of color separation is to use a corresponding color filter, using the principle of complementing each other to perform color separation, so that the basic color light is transmitted and the complementary color light is absorbed, and the complementary color light absorbed is exactly corresponding to a printed color material primary color. Namely: The blue-violet color filter is used for the yellow version, the green filter is used for the red version, and the red filter is used for the cyan version, and the amber filter is generally used for the black version. This shows that people engaged in color separation technology need to have a certain amount of color knowledge, master color light plus color method and color material subtractive color method.
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1 Color Desktop Publishing System Process