Computer image processing is divided into two major categories, namely Vector graphic, also known as vector graphics; and Raster image or bitmap image, also known as raster image. In terms of prepress terms, it is divided into line-work, abbreviated as LW, usually lines, geometric figures and texts; the other is continuous-tone images, English is Continuous-tone, abbreviated as CT, these are A picture made up of pixels. The image obtained by the scanner or digital camera is a bit image, and most of the drawing software (such as lllustraor or Freehand) is a vector image; the font used in the computer is also divided into a bitmap and a vector image, such as PoStipt Type 1 fonts include dot matrix words (for on-screen display) and vector words (for printer output).
Vector graphics
The meaning of a vector is that it can only be expressed in terms of size and direction. Therefore, the vector graphic represents some control points by coordinate values, and the points are connected by lines to form a graphic, so it is also called the outer frame graphic. Because the coordinates and the frame are used to record the graphics, the graphics can be zoomed in and out at will, the effect is the same, and the required memory relative bitmap image is much smaller.
Dot matrix image
Dot matrix means that the image uses a lot of small squares, the term is called Pixel to form the picture of the picture, each pixel is recorded with different colors or shades, so the relative required memory or storage capacity The requirements are great. For example, a square-inch 8-bit gray-tone picture is recorded with a resolution of 300 dots per inch, and a total of 300,000 dots of 300×300 dots is used. When a bit is used to record a point, There are 90, O00byte, which is 88KB capacity.
The above are two commonly used graphics and image recording methods. There are different requirements on different software, fonts and output devices, so it should be clear that the similarities and differences, and then use the appropriate way to use, it is handy.
Image storage format
Based on the above image classification, file format storage is also divided into two categories: Pixel-based format is to describe images, these images are composed of pixels, for example, PhotoShop files are pixel-based.
The Object-based format is the main description of layout files. For example, files made with Illustrator, Freehand, PageMaker, and QuarkXPress are Object-based.
To know the type of file format, you can actually see "Saveas" and "Save a copyas" in PhotoShop at a glance. [next]
PS (FostScript)
PostScript was launched in 1985 by EiAdobe. It is a page description language used to describe text and graphics. It can be used to print brilliant graphic works on paper, film or zinc plate.
Designers can also choose to store as a PostScript file and then deliver it to the output center. Of course, PostScript files can only be exported if they are supported in a PostScript-compatible version.
The biggest benefit of storing as a PostScript file is that the output center does not require desktop publishing software to directly output the PS file. The disadvantage is that it cannot be previewed and modified. If there is a problem with the file output, the output center cannot check or correct the file.
The method of generating a PostScript file is to select the relevant PostScript printer (PPD) and print it into a file in the dialog window of the Print dialog box. The use of PostScript file output in Hong Kong is not very common, because Hong Kong's output center conventions check the documents and placed images before exporting. Because they cannot be arbitrarily changed, not many people will use this file format, but in foreign countries, Common use. PDF is very popular in the near future. Because it can be pre-screened and corrected, when you use Adobe Acrobat Distiller or RIP of prepress system flow to generate PDF, it is necessary to print and store PostScript in PoScript, so you need to know .
EPS (Encapsulated PostScript)
EPS is based on PostScript. EPS can contain a variety of data such as dot matrix, vector, glyph, preview and frame path. It is a versatile file format that is used in a variety of software. It plays an important role in the file format. Most software can store or place EPS files, or generate EPS files through the printing process. There are two obvious differences between EPS and PostScript files. The first is that we can modify the EPS from other software without returning the original file. The second EPS does not have the page size information. The EPS file cannot be generated by printing, but most of the tables. The publishing software can be stored as an EPS file.
Preview - Pre-view part of EPS can be selected lbit black and white or 8bit-256 color, and the resolution is generally 72dpi, which is convenient for other software to work faster. If you want to use Tiff with PC.
Encoding-ASCII is an earlier encoding method. Most of the earlier PostScript Levell and 11 RIPs only support ASCII. Later, the Binary encoding method was introduced. The biggest advantage is that the file is half as thin as ASCll, and the output is faster, but the old version of the software or RIP may not support it. JPEG encoding has compression, but there is distortion, not all software and RIP support, please choose carefully.
Clipping path - If you need to do the retreat, save it as an EPS and store it along with the object-based clipping path before you can put in other software for design and layout. [next]
DCS (Desktop Color Separation)
DCS is a type of EPS format that can be stored in PhotoShop. After the file is stored in DCS, there will be a total of five files, including four color versions of CMYK and a preview file, the so-called "Masterfile".
The biggest advantage of DCS is that the output is faster. Because the file has been divided into four colors, the image transfer time can be shortened by up to 75%, so it is suitable for large file color separation output.
Another advantage is that the production speed is also faster. In fact, the DCS format is an important part of the OPl (Open Prepress Interface) workflow concept. OPI refers to the image with low resolution placed at the time of production, and the high resolution image is connected to the output. This can speed up the production. This workflow concept is especially suitable for some multi-image books or large-box production, so the DCS format is just similar to the OPI concept. When the low-resolution image is placed in the document, the output is output. A high resolution image is connected.
Since the five files are combined to form an image, it is important to note that the names of the five files must be the same, except that C, M, Y, and K are in the original name and cannot change the name of any one.
DCS2.0 is a newer color separation file format, which can include color versions other than CMYK, such as spot color and Hi-Fi Color. It can also be stored as a single file for easy delivery and storage, reducing the occurrence of paper leakage. .
When storing the DCS format, the Preview in the option is a 72dpi RGB image, mainly for screen display purposes, while Composite is a 72dpi CMYK image for printing a color draft.
PDF (Portable Document Format)
PDF translated as a portable file, developed by Adobe, is a cross-platform file format that allows you to open PDF files on any platform such as Mac, Windows, Linux and Unix, as long as you have Acrobat or PDF-compatible readers.
Normally, if you use a certain software to create a file, and some words are used in the file, if someone wants to open the file, they must have the words used in the software and the file; but if the file is used Stored in PDF format, no matter what software is used to make the file, or what type of word is used, others can open this file only by having Acrobat Reader. When the file is saved as a PDF, the elements in the file can be compressed for easy storage and delivery. This file format is gradually welcomed by various industries, such as e-book, CD Rom production and print media. However, it should be noted that the PostScript Levell and ll RIPs do not directly support this format, but the newer PostScript Level III output devices can already output PDF files directly. PDF files that are more suitable for printing can be found in PDF/X format. [next]
PDF/X
In order to meet the needs of prepress and printing, the United States The Committee for Graphic Arts Technologies Standards (CGATS), Digital Distribution of Advertising for Publications (DDAP) and the Newspaper Association of America (NAA) define a suitable output for printing based on PDF. The content was standardized and PDF/X was developed. The first definition is ANSI PDF/X-1:1999, which is based on the PDF1.2 specification; different versions of PDF/X are used to match different workflows.
PDF/X-1a: 2003 (ISO 15930-4:2003)
Suitable for four-color printing is PDF/Xla. This specification stipulates that the font must be embedded. The color mode is CMYK, spot color or grayscale tone. You cannot use RGB or Lab. File size, crop line and bleed should be included in the file; Trapping should be set to “True†or “False†and cannot be set to “Leave Undefindedâ€. It is not possible to encrypt the file. There is no OPI image. The Transparency image function cannot be used. It needs to be flattened first. The JPEG2000 format is not supported.
PDF/X-3:2003 (ISO 15930-6:2003)
PDF/X-3 is an extension of PDF/X-La:2001. The main difference is that PDF/X3 includes RGB or Lab color modes, which are suitable for color tube processes.
PDF/X-2.2003 (ISO 15930-5:2003)
PDF/X-2 is based on the PDF/X-3 specification, but with the addition of OPI functionality.
TIFF (Tagged Image File Format)
Developed by Aldus, it is a pixet-base-based image format widely used in Mac and PC computer software to describe different color data, including 1-bit black and white, 8-bit grayscale and RGB or CMYK color images. . Most software supports the TIFF format. PhotoShop can store clipping paths or alpha channel images together in TIFF format for retiring, but not all software supports.
Byte Order - Since the PC and Mac Tiff format are slightly different, this option actually allows you to choose whether you want to use this image on your Mac or PC. Don't be confused by the noun, just make a choice according to your needs. Yes.
File Compression - LZW Compression is a compression option for the TIFF file format. The LZW (Lempel-Ziv-Welch) compression structure records repeated and repeated data with shorter information. The compressed file quality does not deteriorate, but Not all software and output devices can support this compressed file, so care must be taken when choosing. [next]
PICT
PICT is a native graphics format for the Macintosh system. It is based on the OuickDraw display language and can handle vector graphics and dot matrix image formats. PICT is commonly used for the exchange of software between Mac machines, such as images stored in Scrapbook.
The PICT format supports (16-bit) RGB images of Bitmap, Grayscale, Index Color, and single alpha channel. There are 2-bit, 4-bit or 8-bit/pixel options for grayscale images. There are 16-bit or 32-bit/pixel options for RGB images. PICT is only suitable for non-PostScript output devices, such as general low-end inkjet printers.
JPEG (Joint Photographic Expels Group)
Is a compressed image format with distortion (Lossy). When you choose to store JPEG, there will be multiple levels of compression settings. The highest color is the best, but the file size will be larger. If you choose low color quality, the compression is the largest, and the file is the finest, for example one. The 2MB TIFF is compressed to the lowest quality and is only 88Kbytes. If compressed to the highest quality, it will become 1.1MB.
The original flgJPEG format was originally used to compress images used on Quick Time, and was later used for typography and design because the compressed file transfer speed was faster. Although the file transfer speed is fast, the compressed image quality is low, so the general designer may not use this format.
Prepress exchange file format
When customers and printers exchange data files, it is recommended to use some standard and highly portable file formats that are not related to the software and can be accepted by all those involved in the printing process, and will solve some system and application software versions. Different problems.
In the pre-press production process, there are opportunities to work through different prepress systems. Different operating systems have their own unique output file format. In order to solve the compatibility problem between different file formats, if some common The format is good for exchange.
Here are some common prepress production file formats. If you understand the advantages and use them, you will get twice the result with half the effort. [next]
TIFF/IT
This file format is intended to meet the needs of DDAP (Digital Distribution of Advertising for Publication) magazine publishing, advertising companies, prepress companies and printers. TIFF/IT is a standard for the exchange of digital advertisements and full pages. Only the four primary colors are printed and the spot colors are not supported. The design of this format is very similar to the Scitex CT/LW format, with three files per page. There is also a page file whose function is to establish a connection between CT and LW.
1-bit TIFF
Is a completely dot matrix file, the current RIP workflow can generate two files after rasterizing a file, one is the internal file of RIP, and the other is the 1-bit TIFF of the net. Using a single meta-data, RIP's job is to translate PostScript or PDF files into mechanical 1-bit data, including outlets, like traditional film functions, so the industry calls 1-bitTIFF a digital film.
Delta List
Produced by Heidelberg's Delta workflow, originally created by Linotype-Hell for the Delta workflow; it is a file format that has been interpreted by PostScript (generally referred to as the RIP file format), and then added through the screening Output. Some additional digital copying processes will accept this file format.
Scitex CT/LW
This file format was generated by Creo's Brisque workflow, which was originally owned by Sai Angel. The CT format is an uncompressed dot matrix file, and the LW file contains high-precision image information after dot matrixization. Because of the extremely high precision, the image will be very large, so use RLE compression technology to reduce the size of the file. Since the original LW format can only contain 248 colors and later evolved into NLW, this new format can contain 16,000 colors, making the image contained in the LW smoother.
The Hong Kong printing industry uses a variety of standards-compliant file formats, but it actually relies heavily on workflow to process files. Therefore, for color separation platesetters and printers, it is best to communicate and use what standards to produce the best prints. [next]
Image file compression
Compress image files to increase transfer speed and reduce file storage requirements. File compression has both "lossless" and "lossy". Lossy compression combines similar data, resulting in the loss of the original data in the final decompressed file. The most commonly used image compression type in the printing industry is JPEG (Joint Photographic Experts Group). The larger the "loss" value of the compression setting, the more similar information will be summarized in the same value. Large compressions in lossy types will result in reduced image quality and a large impact on image detail.
The ratio of file compression should not exceed 10:1, which is usually a low compression/high quality setting. However, even at a compression ratio of 10:1 or less, repeated compression and decompression will result in degradation of image quality. For example, an image compressed into JPEG format is decompressed and edited, and then compressed into JPEG format; a compressed image is decompressed for design, and finally saved as PDF, which will cause compression again. This repeated compression/decompression cycle can result in more quality loss.
Lossless compression only combines equal values, so the image is decompressed without loss of quality. Examples of lossless compression include: ZIP and LZW formats, which have a compression ratio of approximately 3:1.
The transmission of digital files does not require data compression, but data compression can speed up the transmission process of large files. The data compression transfer file can only be used if the sender and the receiver agree on the compression method.
Here are some detailed guidelines for using compression software:
• The degree of compression will affect the image quality. Do not use compression with a ratio greater than 10:1. It is best to perform a pre-test to determine the compression method.
• Typically, the recipient and the sender are required to have the same software tools to properly complete the decompression process.
• Do not split the file during compression.
· There are some commonly used compression applications that negotiate with the printer which application to use.
Both compression and decompression processes take up considerable time and hardware resources from the computer, but this is worthwhile because compressed files can be used to get smaller files that the network can handle, thus reducing delivery time.
• If the application software can control the degree of JPEG compression, set the black and white photo to “best quality†and the four color image to “high qualityâ€. This setup not only gives you the advantage of compression, but also guarantees high quality reproduction.
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