1. Chapter III Desktop Imaging Systems & Issues

2. Chapter III, Digital Imaging Systems and Issues: Lesson I Processing Image Data

3. Desktop computer systems, which began as simple text and data processing systems, have evolved into powerful image processing systems. Desktop systems are now capable of performance that, only a few years ago, typified workstations. Developments which have made this possible include:

4. Easy access to high resolution images through scanners, Photo CD, and digital cameras.
The availability of affordable imaging software through commercial channels.

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The availability of affordable memory and an increasing number of high capacity storage options.

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And, the arrival of higher performance, lower cost CPUs which provide the power to process large image files.

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The latest generation processors increase performance in a number of ways: New 32- and 64- bit processors increase overall throughput by moving more data or by reading multiple instructions at the same time. Higher bit depths are like wider highways capable of handling more traffic.

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Some CPUs, known as RISC processors, use a simple or reduced set of machine instructions. Complex operations can then be programmed from these simple instructions, most of which execute in a single clock cycle.

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Caching is another factor significantly increasing performance. A lot of processor time is spent accessing memory for instructions. A cache stores frequently used instructions in high speed RAM, directly accessible to the CPU. This saves processor time, which would otherwise be spent waiting for normal speed RAM.

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Advances in microcircuit fabrication have also enabled faster chip performance. Processors built to operate at higher clock speeds accelerate all processing operations. But clock speed alone doesn't determine how fast a computer will run.

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When a processor is not pipelined it must run back and forth fetching then executing instructions. Pipelining speeds execution by eliminating the waiting time for fetching new instructions. When the processor executes one instruction, pipelining has the next instruction ready and waiting, thus increasing overall throughput.

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Two recently introduced processors which are enhancing digital image processing on the desktop are the Power PC and the Pentium.

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A new generation of Macintosh computers are based on the Power PC, a RISC processor featuring a faster clock, pipelining and caching.

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Compatible desktop systems featuring the Pentium processor also provide faster clock speeds, after pipelining and caching.

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Performance of desktop imaging systems can be further enhanced by adding accelerator hardware. Accelerator hardware usually consists of a RISC processor or a digital signal processor specially programmed to accelerate imaging tasks such as filtering, re-sizing, compression, and color management.

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Another factor enabling desktop computers to handle image files is higher bandwidth internal buses. The bus is a shared highway connecting the CPU with other system components, as well as input/output peripherals. A 32-bit data bus transfers data twice as fast as a 16-bit data bus.

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Macintosh traditionally uses Nu-Bus, a 32-bit self-configuring bus. Simple plug-in installation of cards has made Macintosh computers a convenient solution for imaging system needs.

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PCs have traditionally used the Industry Standard Architecture, or ISA bus which comes in 16-bit versions. The Extended ISA bus or EISA bus has extended this to 32-bits.

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The 32-bit VESA local bus was designed with fewer buffers and delays to increase throughput. The connector slot extends the ISA slot, accommodating 32-bits for greater data flow.

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The 32-bit PCI bus is the latest standard now offered on both MAC and PC. This bus specifies that cards use FIFO or first in/first out transfer which increases the speed of data from the CPU.

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An emerging standard in PC buses is being issued by the Personal Computer Memory Card International Association. The PCMCIA bus was designed to provide high density storage in a compact package about the size of a small stack of credit cards.

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PCMCIA devices are available in three varieties known as type 1, type 2, and type 3. These devices range from RAM cards and FLASH memory to large storage devices such as high capacity hard drives.

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A common bus-related problem for PC users is configuring cards. Selecting base addresses, interrupt and BIOS addresses without conflicts can be frustrating. That's why several computer companies have collaborated to create the Plug and Play specification.

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PCI Local Bus cards incorporating Plug and Play capabilities configure expansion cards invisibly and automatically.