The entire electronic workstation is designed around a compute fig 3-8 . There are three major computer platforms in use for digital photography-the Apple Macintosh, PCs (IBM or compatibles), and Unix-based machines. The most popular computer for digital imaging is the Apple Macintosh. However, PCs and IBM compatibles are also used for digital imaging. They are becoming more popular in the digital-imaging marketplace. Unix-based workstations are used for science-oriented operations and high-volume publishing of books and technical manuals. Therefore, Unix-based machines are not commonly found in Navy imaging facilities.

Regardless of whether you are using an IBM compatible or a Macintosh platform for electronic imaging, the applications are basically the same. Specific computer systems are not covered in this training manual. Only the principles that apply to electronic imaging are discussed.

Computer Configurations

As a guideline, the computer must have a minimum of 8Mb of RAM. For work efficiency, you need at least 32Mb of RAM. Storage may also become a problem because of the large-size file of color digital images. A high-resolution scanned image can require 250 megabytes or more of memory. A hard drive in excess of 600Mb is not uncommon for an electronic-imaging workstation.

The computer system must also have sufficient expansion slots to install interface cards for add-on peripherals, such as scanners, film recorders, and printers. A number of interface cards are available for both Macintosh and PCs that convert analog images to digital format.

Software

Like computer platforms, a vast number of software packages are available for scanning and modifying images. Computer software (programs) makes it possible for you to communicate with the hardware.

Figure 3-R_-Electronic imaging workstation centered around an AT computer.

These software packages are capable of doing more than you could accomplish in a conventional darkroom; they do it much quicker.

Advancements in the development of software packages have made it possible to transform computer imaging from minicomputers or mainframe computers to desktop models. Because software is continually being improved and updated, the application of specific computer software is not addressed in this chapter. Software packages are used to modify and enhance images and to control input and output devices.

DISPLAYS

Most of the computer color monitors available for desktop computers have far less resolution than a digital photograph. A number of graphic boards are available for computers that can produce Super VGA resolution of more than 1,000 by 1,000 pixels on cathode-ray tube (CRT) color displays. A high-resolution, noninterlaced monitor and a 24-bit video card are essential viewing images. A 24bit video card allows for 16.8 million colors to be displayed.

Graphic images displayed on a computer monitor are bit-mapped images. Bit-mapped images are produced by a pattern of dots. Bit-mapped images are sometimes called "pixel-oriented," "raster," or "paint" images. At high resolutions, the individual dots are not discernable.

When you are working on enhancement, modifications, and page makeup of digital images, it is important for you to view what you have done. Therefore, a calibrated color monitor is important so you can see the images or "soft proofing" before you print the images. Monitors for electronic imaging use the additive system. They combine red, green, and blue and add it to the black surface of the screen to create colors.

Monitor quality depends on screen resolution. The finer the pitch of the screen, the sharper the image. The PITCH of the screen is the size of a single pixel. On color CRT screens, a single pixel is composed of three phosphor dots: red, blue, and green. These phosphor dots are struck by an electron gun through a screen or mask. The resolution of the CRT depends on the size of the holes in the mask. The holes in the mask are necessary to direct the electron beam so it strikes the correct phosphor dots as the electron gun scans the screen fig 3-9.

Color monitors are available from standard EGA levels to pixel levels of 2,048 by 2,048. The monitor that is selected for your imaging system must match the display card in the computer, since it is the display card that limits the resolution of the monitor.