3.1
Digital Image Processing
Hardware and Software Functions

John R. Jensen Department of Geography University of South Carolina Columbia, South Carolina 29208 Direct Comments to: jrjensen@sc.edu

Introduction

Adigital image processing system is the combination of the computer hardware and the image processing software.

Basic computer hardwares for digital image processing:

Image analysts perform digital image processing on mainframe computer systems, workstations, or personal computers (Russ, 1992). The major difference is in the speed at which the computer processes millions of instructions per second (MIPS). Mainframes are generally more efficient than workstations which perform better than personal computers. The MIPS being processed on all types of computers is increasing logarithmically while the cost of a computer per MIP is decreasing.

Mainframe computer

A mainframe computer system (> 32-bit central processing unit - CPU) usually uses batch or interactive mode from relatively dumb, alpha-numeric terminals. The advantage of the mainframe computer system is its high speed performance in routine processing. The disadvantage of the mainframe computer system is its coarse output (alphanumeric overprint or line plotter) and only occasionally have the opportunity to view the remote sensor data on a high resolution black-and-white or color monitor.

Workstation
Workstations (>32-bit CPU) are relatively inexpensive and generally consist of a sophisticated reduced instruction set computer (RISC) interfaced to a high resolution color display. RISC workstations function independently using their own operating system, CPU, and digital image processing software. They may also be networked (connected) to other workstations or to a file-server which contains the image processing software and remote sensor data. RISC workstations process information as rapidly as many mainframe computers, thus the distinction between mainframes and workstations is becoming less distinct (Berry, 1993).

Personal Computer
A personal computer (PC) system (16- to 32-bit CPU) with the appropriate software may perform relatively sophisticated digital image processing. Typical machines cost < $1,500 including a color monitor with an 8-bit (256 color) look-up table. Educators often purchase PC based digital image processing systems because they are able to configure numerous systems for laboratory instruction at reasonable cost. PC maintenance agreements are also relatively inexpensive when compared to those for mainframes and workstations. Recently, the available of X Window Server software make the PC functioned as a part of the networked workstations that largely broaden the functionality of the PC systems.

Basic software functions for digital image processing:

The most important functions typically performed on digital image processing systems are summarized in Figure 3-1. Every function listed may now be performed on personal computer digital image processing systems as well as workstations and mainframe computers.

Figure 3-1
Hypothetical
Workstation Network

Image Processing Functions Found in Many Image Processing Systems

Preprocessing

Radiometric correction (for sensor system and environmental effects)
Geometric correction (image-to-map, or image-to-image)

Display & Enhancement

Black & white, color-composite display
Density slice
Magnification, reduction, roam, pan
Transects
Contrast manipulation
Image algebra (band ratioing, image differencing, etc.)
Spatial filtering
Edge enhancement
Principal components
Linear combinations (e.g., Kauth transform)
Texture transforms
Frequency transformations (Fourier, Cosine, Hadammard, Walsh etc.)
Digital elevation models (DEMs)
3-dimensional transformations
Animation
Image compression

Information Extraction

Supervised classification
Unsupervised classification
Contextual classification
Incorporation of ancillary data during classification
Radar image processing
Hyper-spectral data analysis
Soft copy photogrammetry to extract digital elevation models
Soft copy photogramemtry to extract orthophotographs
Expert system and/or neural network image analysis

Image Lineage

Complete image or output GIS file history

Image/Map Cartographic Composition

Scaled postscript level II output of images and maps

Geographic Information Systems (GIS)

Raster (image) based GIS
Vector (polygon) based GIS (must allow polygon comparison)

Integrated Image Processing and GIS

Complete Image Processing Systems (Functions 1 to 23)
Complete Image Processing Systems and GIS (Functions 1 to 33)

Utilities

Network (Internet, local talk, etc.)

Go to Section 3.2 - Commercial and Publicly Available Digital Image Processing Systems

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References

Berry, F. C., 1993, Inventing the Future: How Science and Technology Transform Our World. Washington, DC: Brassey's, 180 p.

Jensen, J. R., 1996, Introductory Digital Image Processing: A remote sensing perspective, 2nd Edition. NJ: Prentice-Hall, pp. 66-67.