DISPLAYING UNDERSAMPLED IMAGERY

Standard digital video displays use 640x480 (NTSC) or 512x512 (PAL) pi xels to display a full screen image, while observers searching such im ages for small targets (or reading text) will typically operate with a screen subtense of 25x35 deg. Often, however, the region of interest in these images may be about 100x100 pixels in size, and so subtend on ly about 5x5 deg on a standard screen. In this case enlargement-that i s, increasing the angular subtense-of the region of interest may well be appropriate. To obtain a larger viewing angle, the image must be zo omed, with some form of interpolation being used to generate new inter mediate pixels. This paper reports on two experiments in which the eff ects of various methods of zooming on target acquisition are psychophy sically evaluated. The results show that zooming generally enhances pe rformance, but that for zooming factors greater than 2, smooth zooming techniques need to be used.