Print Image Information Processing - Color Desktop Publishing System

Section Five Color Desktop Publishing System

The color desktop publishing system, also known as DTP, is an abbreviation of Desk Top Publishing, and is named for its small size that can be placed on the desktop.

The color desktop publishing system is a new type of prepress processing equipment introduced in the 1990s. It is composed of desktop color separation and desktop electronic publishing. Its advent, fundamentally solved the electronic color processing machine text function is weak, can not be a good production of graphic and textual negative film or film defects.

The color desktop publishing system is divided into three major parts: output, processing, and output.

First, DTP input device

The basic function of the input device is to scan, color-separate, and enter the system. In addition to text input and computer typesetting system, the image input can use a variety of devices, such as: scanners, electronic color machines, cameras, plotters and satellite ground receiving stations. Mostly used scanners.

Scanners are available in both flatbed and roller versions. Scanners for color desktop publishing systems should have input resolution, color number of bits, and scan density range suitable for printing requirements.

(a) The input resolution refers to the number of points sampled per inch and is expressed in dpi. Dpi and outlet line lpi have the following relationship:
Dpi (input resolution) = number of dot lines × scaling factor × coefficient

The coefficient is generally 1 to 2. As the magnification increases, the required resolution increases. The magnification of the reflected manuscript is small, and it can be calculated by 5 times and 1500 dpi is sufficient. The width of the transmitted manuscript is small, calculated at 10 times, 3000 dpi only. Some scanners have a resolution of 6000-8000 dpi. The actual resolution used depends on the resolution of the output resolution and the zoom factor of the image.

(b) Color number and scanning density range

The number of color bits refers to how many bits are used for a certain color, such as 8-bit, 16-bit, 24-bit, and 36-bit. The scan density range refers to the density difference in the lightest and darkest places. Generally, the larger the scan density range, the larger the number of color bits, and if the density range is greater than 3.0, at least 10 bits.

In addition, the scanner is required to provide a standard universal data format, accurately and reliably accept the control of the workstation, has an automatic environment correction function, can compensate for external light interference, and on the premise of ensuring that the main technical indicators of the scanner are met, The faster the scanning speed, the better.

Second, DTP processing equipment

Processing equipment is collectively referred to as a graphic workstation. The basic function is to process the manuscript data entering the system, such as: color correction, revision, imposition and creative production, plus text, symbols, etc., to form a complete picture-text page, and then transmitted to the output device.

Currently, the computer used has a mac camera (MAC)? PCs and workstations, etc. Since the hardware devices and software that can be used on the desktop system are extremely rich, when selecting a hardware and software combination suitable for printing requirements, considerations such as processing speed, processing capacity, system network, and Chinese environment should be considered.

(1) Processing Speed ​​Image processing requires point-by-point processing of the points in the image. The amount of data is large, and it requires a very high speed. A higher-grade microcomputer or workstation should be used.

(2) Processing capacity image processing Since the requirements for input resolution and output resolution are becoming higher and higher, workstations are required to process data with increasing capacity. It also requires the storage of a large number of ready-made libraries and fonts.

(3) If the work of the system network color desktop publishing system is connected to the network, multiple computers will jointly complete a task and people will enjoy expensive scanning and recording equipment. Therefore, it is necessary to choose a reasonable system network and network server and file server for support.

(4) The development of various applications of foreign languages ​​in the Chinese environment is very rapid. It is not possible to use the new application software after it is finished in Chinese. This requires the workstation to have a good Chinese environment and good compatibility with the open performance. It can put new The Western-style software that was opened was directly ported to the system's Chinese environment without any problems.

Third, DTP output device

The output device is the device that the color desktop publishing system generates the final product. It is mainly composed of a high-precision laser imagesetter (also called a graphic recorder) and a RIP (raster image processor). The laser image-setter uses a laser to collect the light beam into a light spot, strike the light-sensitive material to make it light-sensitive, and develop it into a black-and-white negative film. The RIP accepts the layout of the Postscript language, converts it into a raster image, and outputs it from the imagesetter. (Postscript is a page description language developed by Adobe. Now it is accepted by many people and becomes a standard.) RIP can be implemented by hardware or software. Hardware RIP consists of a high-performance computer plus dedicated chips. Software RIP consists of a high-performance general-purpose microcomputer and corresponding software. In order to meet the requirements of image processing for printing, the output resolution, output repeatability, output screening structure, and output speed of laser image-setter and RIP must be considered.

(1) The output resolution text resolution is generally 700 to 900 dpi, and the image resolution is 60 lines/cm. The resolution requires 2400 dpi, and 70 lines/cm requires 3200 dpi.

(2) Reproducible output precision fine prints, with a maximum allowable error of 5 μm. General prints such as manuals, books and periodicals, allow for repeatability of 20 to 25 μm. Low-grade prints, such as colored newspapers, have an error tolerance of 25 to 50 μm.

(3) The output screening structure can output dots of different dot lines and dot shapes. In order to ensure that the color image is not copied, there is no obvious tortoise or density fluctuations, and the output device is required to produce dots with good printing performance.

(4) Output Speed ​​The output speed depends on the performance of RIP and teletext recorders. Hardware RIP is fast and software RIP is slow. With the same mass of color separations, the faster the better.

In addition, the output device should also have a standard interface and the ability to output Chinese characters, and the output format can meet the printing requirements.

The output devices of the color desktop publishing system also include various color printers such as laser printers, inkjet printers, thermal printers, and various multimedia carriers (slide makers, optical disks, video recorders, etc.).

Fourth, high-end networking

The color desktop publishing system is associated with various existing electronic color separation machines and is called high-end networking. This is yet another working method of the desktop system.

When using high-end networking to obtain high quality graphic negatives, the electronic color separation interface must address two key issues. First, the speed issue. Due to the fact that the electronic color separation machine cannot be paused at the time of its state and state, the interface and interface workstation must be fast enough to simultaneously receive the scan data of the electronic color separation machine and send data to the electronic color separation machine. Second, the picture and text output the way of film. If the dot generator of the electronic color separation machine is used to generate dots, only one high-resolution interface is added to jointly complete the graphic and text output. If you do not use dot generators of the electronic color separation machine to generate dots and only treat the recording part of the electronic color separation machine as an imagesetter, you need to add another RIP processing dot and text. The desktop system uses the electronic color separation machine through RIP. .

High-end networking has formed a full-page imposition system with a general-purpose computer as its core. Not only does the electronic color separation machine have a high input resolution and good image processing quality, but it also integrates the desktop system to handle text and text simultaneously. It is flexible, fast, creative, and full-page data can be accessed repeatedly. For manufacturers with electronic color separation machines, improving the ability and efficiency of color platemaking has opened up an excellent way.