Chapter 9 - Goodheart-Willcox

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Figure 9-15. Encoding options available when saving a file using the JPEG compression option. digital document result in a very large file. EPS-JPEG compression creates files for incorporation into page composition software that are significantly smaller than standard EPS files. Images vary in amount of compressible data without detracting from visible quality. The user should experiment with quality settings to determine the maximum compression usable without perceptibly altering appearance. Since data is lost in each compression/decompression cycle, experienced users recommend using JPEG compression only on final images, and using it at the maximum quality setting, Figure 9-16. Figure 9-16. JPEG compression should be used at maximum quality to preserve the integrity of the data being compressed. <strong>Chapter</strong> 9 Electronic Prepress and Digital Printing 183 File Formats Many different file formats exist; each type varies in the way images are saved, how they can be modified, and how well they will reproduce. File formats contain a number of important aspects, including image placement, resolution, color, and background. The following are some of the most commonly used formats. Tagged image file format (TIFF or TIF) The tagged image file format (TIFF or TIF) is a raster graphic file used for exchanging bitmapped images between applications. Depending on the source application, a TIFF file can allow lossless or JPEG compression. The format supports bitmap, grayscale, RGB, CMYK, and indexed color models. It also allows the inclusion of embedded paths and alpha channels. TIFF files can be exchanged among several platforms, including Mac OS, DOS, PC, and UNIX. Tagged image file format for image technology (TIFF/IT-P1) The tagged image file format for image technology (TIFF/IT-P1) is a device-dependent format used for describing four-color documents, including specifications for printing presses. TIFF/IT-P1 is a raster-based input format designed to be used with high-end CEPS (Color Electronic Prepress Systems). It is favored by the magazine industry for digital delivery of color advertising files. The P1 or “profile one” component was added when the format was accepted by the International Standards Organization (ISO) for consideration as an international standard. TIFF/IT-P1 is designed to reduce the need for additional time and labor created when CEP systems cannot communicate easily. Encapsulated PostScript (EPS) The Encapsulated PostScript (EPS) is one of the most stable of the file formats used in outputting to an imagesetter. It is less convenient than a TIFF but will usually provide more stable results when output. EPS provides a very reliable format for graphic images because it handles both vector and raster images. 184 Graphic Communications The EPS format allows inclusion of low-resolution previews for screen display and nonPostScript printing. It is also possible to display just a box with the file name of an image instead of the image itself, Figure 9-17. The EPS format supports bitmap, grayscale, RGB, CMYK, spot color, and indexed color models. Figure 9-17. Since image files are usually very large and tend to slow a system down, the EPS file format allows the user to display just a box with the filename of an image instead of the image itself. EPS files also allow the inclusion of open press interface (OPI) comments and the creation of embedded paths. The open press interface (OPI) file format allows the replacement of low-resolution images in files from one system with high-resolution image files on another. If saved in ASCII data format, EPS pictures can be opened and read in a text editor. Windows Metafile (WMF) and PICT The Windows Metafile (WMF) is the Windows 95/NT version of the PICT file format. The PICT is a Mac graphics file based on the original Mac OS QuickDraw drawing routines. Both the WMF and the PICT format can hold both bitmapped and object-oriented images. The original PICT format could only support 8 colors, but a newer version called PICT2 supports up to 256 colors. Desktop color separations (DCS 1.0 and DCS 2.0) The desktop color separations 2.0 (DCS 2.0) file format is an EPS graphic saved as a single file that can include up to six plates (cyan, magenta, yellow, black, and two spot colors) and a master image. The master file is used for composite printing. The DCS format supports grayscale, RGB, spot color, and CMYK color models. DCS files print faster than standard EPS files and can contain both bitmap and object-oriented information. The desktop color separations 1.0 (DCS 1.0) creates five separate files, one for each process color (CMYK), and a data or master file. DCS 1.0 is also referred to as five-file format. The Photo CD The Photo CD or proprietary Eastman Kodak Company format is designed for storing compressed photographic images on CD-ROM. It can only contain raster information. The format supports grayscale, RGB, and CIELAB color models. The digital images can be viewed on-screen or retrieved with the proper system. Graphics interchange format (GIF) The graphics interchange format (GIF) was originally designed by CompuServe to transfer graphic files between computer systems. GIF files can support only raster images, but can handle up to 256 colors, and various resolutions. GIF includes data compression, making it especially effective for scanned photos and a popular graphics format for images on the Internet. Autotracing Some graphics programs incorporate an autotracing feature. Autotracing is a process for converting a raster image into a vector image. Most autotracing packages read files in a variety of bitmapped formats (PCX and TIFF are the most common) and produce a file in a vector format such as an EPS. The conversion techniques used, and the accuracy of the conversion process, differ from one package to another. File names File naming conventions are often overlooked or even ignored. However, carefully naming your files will help keep your work organized. Whether
you create a standard in-house convention or take advice from your service bureau, the format must be applied in a consistent manner. Computer platforms and programs are subject to their own conventions. Macintosh file names should be kept under 20 characters in length, and although the latest versions of Windows allow file names to contain up to 255 characters, PC file names should be limited to less then 20 characters with a three character extension. In addition to these builtin limitations, there are several general rules you should follow. ■ Only alphanumeric characters should be used. The use of symbols should be avoided. ■ File names should not begin with a space. ■ Each file name should be unique. ■ The appropriate file extensions should be used to identify file type, such as .TIFF, .EPS, or .FPO. To avoid confusion, revised files should not be submitted with the same name as the original file. However, if you are using automatic picture replacement (APR) or OPI files, it is important that you do not rename them. The name of the file serves as the link to the high-resolution image and changing the name will cause delays while the link is reestablished. Internal and External Storage Devices Every computer system comes with a certain amount of physical memory, usually referred to as main memory or RAM. RAM is the short-term memory the computer uses to store information in process. Systems can be updated and memory capabilities can be increased to support additional programs. In addition to having a computer system that is capable of running your programs, you must have some means for storing and transmitting data. The term memory identifies data storage that comes in the form of chips, while the word storage is used for memory that exists on tapes or disks. Although compression methods can be used to reduce file size, most page composition files remain very large. Fortunately, there are many types of storage devices available that will accommodate large files. Storage devices vary in terms of size (physical and memory), access capabilities, speed, <strong>Chapter</strong> 9 Electronic Prepress and Digital Printing 185 reusability, and integrity. Storage capacity is measured in kilobytes (1024 bytes), megabytes (1024 kilobytes), and gigabytes (1024 megabytes). Disk storage There are two basic types of disks, magnetic and optical. (A disk is a round plate on which data can be encoded.) Data is encoded as microscopic magnetized needles on a disk’s surface. You can record and erase data on a magnetic disk any number of times, just as you can with a cassette tape used for recording music. Magnetic disks come in a number of different forms, including hard and floppy. The hard disk drive, or hard drive, is a machine that reads data from and writes data to a hard disk. Hard disk drives are usually built into the computer system. The hard disk drive contains one or more permanent aluminum hard disks coated with a magnetic material, Figure 9-18. The aluminum disks are rotated very quickly and a read/write head moves over the disk surface, which contains densely packed magnetic tracks. The read/write head is used to write (record) or read (retrieve) information as the magnetic tracks spin past the head. Storage capacity varies and can be increased by adding another hard drive, replacing your hard drive with a higher-capacity one, or using a new configuration known as RAID (redundant array of independent disks), Figure 9-19. Figure 9-18. Storage capacity varies and can be increased by adding another hard drive or replacing your hard drive with a higher-capacity one. 186 Graphic Communications Figure 9-19. RAID storage devices consist of a base unit, expansion units, and a removable cover. Most configurations are hot-swappable, allowing the removal and replacement of failed drives or power supplies without shutting down the system. (The RAIDinc Cobra LTE, courtesy of RAID, Inc.) RAID offers almost unlimited storage capacity. The RAID configuration connects a number of highcapacity hard disk drives together to act as a single huge hard drive. In addition to increased storage capacity, RAID increases file-access speeds and data-transfer rates while providing varying degrees of data protection and failure-proofing the storage subsystem. RAID continually copies data to each of its drives so, if and when a drive crashes, it can be replaced without system downtime or loss of data. Removable hard disk drives are often referred to as removable cartridge devices. Removable hard drives are hard disks encased in a metal or plastic cartridge so you can remove them just like a floppy disk. Removable hard disk drives are very fast (often faster than fixed hard disks) and have a typical storage capacity ranging from 60 Mb to 250 Mb. Floppy disk drives function in the same way as a hard disk drive but they use a removable disk known as a floppy disk. Floppy disk drives are relatively slow and have a limited capacity, making them unsuitable for graphics applications. Floppy disks, however, are portable, inexpensive, and fairly reliable for text files. A high-density 3 1/2″ floppy disk can hold 1.44 Mb of data. Hard disk drives are from two to 20 times faster than a floppy so it is recommended that you work from your hard drive and save to the floppy. ZIP, JAZ, and SyQuest SparQ disks are essentially floppy disks with a vast amount of storage capacity. The disks themselves are, like a floppy disk, 3 1/2″ in size, but they are twice the thickness and can typically store more than 100 Mb of data. Some disks can hold over 1 Gb of data. Special ZIP, JAZ, and SparQ disk drives are required, Figure 9-20. Figure 9-20. ZIP drives are available as external or internal units. Unlike floppy and hard disks, which use electromagnetism to encode data, optical disk drives use a laser to read and write data. Optical disks have very large storage capacity but they are not as fast as hard disks. Five and one-quarter inch opticals may hold up to 2.3 Gb of digital information per side while 3 1/2″ opticals hold 230 Mb. The less expensive optical disk drives are read-only. Read/write optical disk systems record data by burning microscopic pits in the surface of the disk with a laser. To read the disk, another laser beam shines on the disk and detects the pits by changes in the reflection pattern. Optical disks have a much larger data capacity than magnetic disks. Optical disks come in three forms, CD-ROM, WORM, and erasable optical. CD-ROMs are read-only disks, Figure 9-21. You can read the data from a CD-ROM but you cannot
Page 1 and 2: This sample chapter is for review p
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Page 13 and 14: Final product Press proof Printing
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