The Effect of Polarity on Object Recognition in Thermal Images

Abstract

Thermal imaging (TI) systems, transform the distribution of relative temperatures in a scene into a visible TV image. TIs differ significantly from regular TV images. Most TI systems allow their operators to select preferred polarity which determines the way in which gray shades represent different temperatures. Polarity may be set to either black hot (BH) or white hot (WH). The present experiments were designed to investigate the effects of polarity on object recognition performance in TI and to compare object recognition performance of experts and novices. In the first experiment, twenty flight candidates were asked to recognize target objects in 60 dynamic TI recordings taken from two different TI systems. The targets included a variety of human placed and natural objects. Each subject viewed half the targets in BH and the other half in WH polarity in a balanced experimental design. For 24 out of the 60 targets one direction of polarity produced better performance than the other. Although the direction of superior polarity (BH or WH better) was not consistent, the preferred representation of the target object was very consistent. For example, vegetation was more readily recognized when presented as dark objects on a brighter background. The results are discussed in terms of importance of surface determinants versus edge determinants in the recognition of TI objects. In the second experiment, the performance of 10 expert TI users was found to be significantly more accurate but not much faster than the performance of 20 novice subjects.

Enhanced/Synthetic Vision Systems: Human Factors Research and Implications for Future Systems

“…Additionally, in a separate study, the specific gray-shade mapping for IR non-terrain targets has also been found to influence recognition. Brickner and Zvuloni (1991), found that IR polarity, the mapping of black to hot or white to hot, strongly affected the ability to recognize non-terrain objects. Thus, for non-terrain targets, it appears that IR imagery improves recognition performance over direct vision or TV (due to display parameters), but that the gray-shade mapping can also affect recognition.…”