Color Desktop Publishing Q & A (4)

1. What is Postscript language? Postscript is a page description language developed by Adobe in the past based on a language oriented for three-dimensional graphics, and developed in 1985. It is an interface language output from the desktop system to photosetting devices, specifically for describing images and texts. And design. The function is to record the image text on the page, use a digital formula to record and run on a computer, and finally translate it into a desired output through a Postscript decoder, such as being displayed on a screen or output on a printer or a laser image-setter. Postscript language is the most popular form of page description language in the world. It has a large number of graphic operators that can be used in any combination. It can describe and process text, geometry, and external input graphics. Theoretically speaking, it can describe arbitrary complexity. The layout. The success of its design using this page description language has become a choice for many manufacturers. Its rich graphics capabilities and efficient description of complex layouts have attracted support from publishing software and graphics software. Nearly all prepress output devices support PS language, and the success of PS language also makes Open electronic publishing systems are widely used internationally. In the late 1980s, it became a de facto industry standard. After years of experience and feedback from many PS products, PS2 was introduced in 1990 and PS3 was further introduced in 1990. How is the gray level of the output device calculated? High-end DTP systems are usually equipped with laser imagesetters with output resolutions above 3000DPI. The gray scale of the output device can be calculated according to the following companies: Output device gray scale = (output resolution / number of network lines) 2 + 1 If the output resolution of the laser imagesetter is 2400 DPI, using 150 lpi, you can get its output gray Degree is 255. The gray level that can be distinguished by a person's naked eye is about 140 levels, and visible 255 levels greatly exceed this range, fully meeting the requirements of high-end products. The above company can be rewritten as: output resolution = sqrt (number of gray levels - 1) * number of lines. According to this formula, the closest resolution to meet the requirements can be calculated so that the output time of the imagesetter can be optimized. 3. What is digital proofing? Traditional proofing is to print plates with negative or positive pictures, and then use printing plates for proofing. In recent years, due to advances in computer image processing technology, color desktop publishing systems and color electronic prepress systems that integrate text and image processing have developed rapidly in the field of professional printing, and the requirements for digital printing systems that are compatible with them have also increased. more and more. The digital proofing system uses the prepress data before the negative or positive image is generated. The digital proofing system does not produce the intermediate media-film but directly produces the proof using the digital output method. It is a kind of proofing method to output digital color image information directly on the paper by dot-tone or other methods to simulate the printing effect. Digital proofing includes silver salt photography, inkjet printing, thermal sublimation, and color laser printing. 4. What is RIP and what is the basis for measuring RIP performance? RIP is an acronym for Raster Image Processing. When used as a noun, it refers to hardware or software that translates a PS code into a bitmap image in a photo system. Commonly referred to as raster image processor. It has a very important role in the electronic publishing system of the color prepress system. Its role is to quickly interpret the page description language from the workstation or server as a dot matrix command that can control the output of the laser recording device. It will act like an automatic electronic translator that can arrange the text image in the computer software. , Lines, graphics, etc., are automatically converted into digital image data, and these dot matrix data are sent to the recording equipment. They control the "yes" and "nothing" of the laser spot like a switch, and they are arranged well. Layout results are output to film. RIP's screening processing algorithm and high-speed text recovery technology (including Chinese character processing) are the main basis for measuring RIP performance. Second, RIP's compatibility with file formats and multi-functional support technologies such as trapping and color separation have also become a very important indicator of RIP. RIP verbs may be translated into "rasterization" or "matrix processing." 5. What is the working principle of OPI? Regardless of user systems or operating platforms, OPI is a relatively straightforward process. After an image is scanned at high resolution or entered into a computer, it will be saved as a document file or image file. The OPI operator will sub-sample the image to create a low-resolution alternative image. This low-resolution FPO image is usually saved in TIFF or EPS format depending on the original image. In order to match most desktop displays, FPO format images are often stored at 72 dpi. Because the OPI sample generator can recognize multiple document formats, it is easy to create low-resolution FPOS format images for preview use. Some original drawings must use special application software to watch. For example, some applications cannot read the SHLW format, or cannot use TIFF images that are compressed by some CCITT compression format. The most common document formats include TIFF, EPS, DCSV1 and V2, Scitex Handshake CT. and JPEG (these are the minimum formats that should be supported by any OPI server). Some other formats include Scitex Handshake Lw, Copy Dot TIFFS and Photoshop Mative. In order to make the layout easier, the designer fetches the FPO image from the server, arranges, crops, rotates, etc., and saves it. When the document is output to the PS device, two things happen. First, OPI writes a series of contents. These describe the position and characteristics of the FPO image on the page (cropping, scale, rotation), and also write down the image's name and path to find the location of the high-resolution image on the server, then the OPI image The server performs image conversion and sends large PS documents to RIP for processing output. According to this system, high-resolution documents can be (1) separated before being stored in the server; (2) separated by the OPI on the server ( 3) Save as a composite file separated by RIP.