In the prepress processing system, the commonly used page description language is Adobe's Postscript language. Page description language is a general-purpose programming language with strong graphic functions. Its main function is to describe text, graphics and images on the output page. Since this description is completed by extracting graphical entities, the description is of high quality, cost-effective, and has nothing to do with equipment.
1. Basics of Postscript-based printing page programming
1. Features of Postscript language
From the perspective of the PS language itself, on the one hand, it is a general programming language with strong graphics functions, and on the other hand, it is a page description language with the characteristics of general programming languages. In other words, Postscript has the dual characteristics of general programming language and page description language. In summary,
PS language has the following main features:
â‘ With some basic structures of general programming language, the page information described by Postscript is compact and effective.
â‘¡ With powerful text, graphics and image processing functions.
It can be composed of straight lines, arcs and cubic curves of any shape. The graphics can be self-intersecting or contain unconnected parts and holes; the filling operation allows the contour lines of the graphics to be any shape and any width; the clipping path can be any shape; fill Colors can be specified through Grayscale, RGB, CMYK, CIE-based, etc. It can also be repeated patterns, smooth gradients, color mapping and spot colors; the text is completely processed as graphics, so any graphics operator in PS language is also applicable For text; PS language can describe the sampled image at any resolution according to different color models, providing the function of processing and outputting the sampled image; In the universal coordinate system, PS language supports compounding composed of linear transformations such as translation, transformation ratio and rotation Transformations, and these transformations apply to all elements of the page description, namely text, graphics and images.
2. The basic method of Postscript page graphic description
The most remarkable feature of PS language is that it has a powerful page description function. According to the imaging model proposed by Adobe, the PS language simplifies the description of the graphics on the page into two basic processes: construction path and coloring path. Through these two basic operations, geometric shapes of arbitrary shapes can be generated.
â‘ Path structure.
Postscript path is a method to define various shapes, trajectories and areas. Paths are used to draw lines, specify the borders of filled areas, and define templates for cutting other graphics. The path is composed of straight and curved segments. These line segments may or may not be connected to each other. The topology of the path is not limited. It can be convex or concave. It can contain multiple closed sub-paths, so Represents several areas, and the paths can intersect themselves in any way.
The path is represented by the internal data structure of the Postscript graphics mechanism. Although the path is not directly accessible like the Postscript object, its construction and use are completely under the control of the Postscript program.
â‘¡ Coloring processing and graphics generation.
Shading operators represent the marks on the current page by transforming geometric scans into raster memory. Commonly used shading operators are stroke and fill. The more specialized operator is image.
â‘¢ The characteristics of Postscript characters and fonts.
In the PS language, the text is composed of a series of Postscript characters, and any Postscript character is a graphic that can perform any graphic operation. It's just that they have different shapes, and these graphic shapes are composed of a Bezier curve segment and a straight line segment.
Font resource is one of the most important resource classes provided by PS language. It is a collection of various characters, which contains the definition of character shape path. Since characters have multiple font attributes, the character shape when the same character is in different fonts is different. Therefore, Postscript stores the character definitions of a font in a font resource instance, such an instance is a font. As a resource, the font is usually loaded into the virtual memory by the interpreter only when needed by the Postscript program. Usually, fonts exist in the form of program files, so a font is a "font program". When the interpreter encounters findfont, it will execute a font program according to the font name provided by its operand object, thereby creating a font dictionary and storing it in global or local virtual memory. Generally, the font name is always represented by the corresponding font name with the prefix “/ ', such as / Helvetica, / Times-Roman, etc.
Since the Postscript font is defined by vectors, the Postscript characters can be scaled arbitrarily without distortion or aliasing. Therefore, it is only necessary to define a character shape of a size in the Postscript font library, and corresponding characters of any size can be obtained by scaling the character coordinate system.
â‘£ The process of processing text in a graphical manner.
The PS language treats any character as a graphic, and the description of the character path is included in the font resource provided by Postscript. The Postscript program can call these character paths as long as the corresponding font is used. PS language control text output includes two major processes, namely setting the current font and displaying characters.
Morden French Nails,Double French False Nails,Double French Press On Nails,Longlasting Press On Nail
Zhong Shan Senboma Artware Co.,Ltd , https://www.senbomanails.com