Introduction

Information density in displays in increasing rapidly with the phenomenal growth of data and graphics displays. The introduction of color to data and avionics displays has required improvement of the shadow-mask CRT, which heretofore had only limited resolution demands place on it, mostly for television use. The color shadow-mask CRT requires special considerations when measuring resolution to avoid anomalies caused by the physical structure of the screen. All of this has renewed interest in display resolution and resolution measurement.

The resolution of date displays and data-display cathode-ray tubes is a most difficult parameter to characterize accurately. Large difference in resolution measurements are often observed, due to the diversity of display formats, such as raster scan and stroke writing, alphanumerics and graphics. The large diversity of measurement techniques also produces differing results. Differences in test operator perception and skills and to the problem. Resolution data should therefore be used with caution. Figure 1 shows some of the major sources of resolution measurement error.

When comparing displays or CRTs, the display engineer must be sure that resolution data are comparable. A display form manufacturer A specified as having 20-mil resolution at the half-amplitude points with 200-microampere beam current may actually have better resolution than a display from manufacturer B specified as having 10-mil spot size measured with the shrinking-raster technique at 100 microamperes. It's the age-old "apples-and-oranges" problem again.

The resolution of CRT display may be expressed in any of several ways, including:

• spot size

• line width

• number of TV lines

• modulation depth at a specified spatial frequency

• MTF curve

Each of these measurements has differing connotations ad is not usually directly comparable to the others, especially if drive or duty-cycle differences are considered.

Resolution may be measured in an even greater number of ways, as shown in Figure 2. It is the purpose of this paper to present information on as many techniques as possible.