INTRODUCTION

A great deal of confusion exists about the precise meaning of the terms Resolution and Addressability as applied to display systems, Additionally, once clarity of meaning is achieved, the problem remains of designing a system in which these two quantities are properly related to each other to maximize the quality of the displayed image. Such a relationship is one in which the image meets some perceptual cfiterion of image quality. This paper, then, is concerned with clarifying the meaning and specification of resolution and addressability in Cathode-Ray Tube (CRT) based display systems arid with presenting a visually derived metric for selection of the optimal relationship of resolution and addressability .

In essence, resolution is a property of the design of the display device. It is derived from the width of a line or spot imaged on the screen: The narrower the line or the smaller the spot, the higher the resolution. From the measured line width, resolution can be specified in a number of ways, such as lines per unit distance, Modulation Transfer Function (MTF), spot size, etc. We will consider the line width at 50% of the maximum luminance intensity, since simple conversions exist to translate the various metrics of resolution [1],[2].

Addressability is a characteristic of the display controller and represents the ability to select and activate a specific point of x,y coordinate on the screen. On rastered displays, this is usually stated in terms of the number of lines scanned from the top to the bottom of the display screen as well as the number of points along each raster line.

Since addressability is controiled by the hardware driving the CRT, and since resolution is determined by the design of the CRT, these two display characteristics are independent of one another, However, to obtain high levels of image quality, certain relations need to be maintained between resolution and addressability. For example, if resolution is too low (large spot sizes), successive lines will over-write preceding lines. Under some conditions, this may produce image artifacts such as false contours. Conversely, if addressability is too low (large spot separations), then adjacent raster lines will not merge and they will appear as visible stripes.