TRIANGLE ORIENTATION DISCRIMINATION - THE ALTERNATIVE TO MINIMUM RESOLVABLE TEMPERATURE DIFFERENCE AND MINIMUM RESOLVABLE CONTRAST

The characterization of electro-optical system performance by means of the minimum resolvable temperature difference (MRTD) or the minimum r esolvable contrast (MRC) has at least three serious disadvantages: (1) the bar pattern stimulus is theoretically and practically unsuitable for 1-D or 2-D spatially sampled systems such as pixel-array cameras, (2) spatial phase is not taken into account, and (3) the results depen d on the observer's subjective decision criterion. We propose an adequ ate and easily applicable alternative: the triangle orientation discri mination (TOD) threshold. The TOD is based on an improved test pattern , a better defined observer task, and a solid psychophysical measureme nt procedure. The method has a large number of theoretical and practic al advantages: it is suitable for pixel-array cameras, scanning system s and other electro-optical and optical imaging systems in both the th ermal and visual domains, it has a close relationship to real target a cquisition, and the observer task is easy. The results are free from o bserver bias and allow statistical significance tests. The method lend s itself very well to automatic measurement, and can be extended for f uture sensor systems that include advanced image processing. The TOD c urve can be implemented easily in a target acquisition (TA) model such as ACQUIRE. An observer performance study with real targets shows tha t the TOD curve better predicts TA performance than the MRC does. The method has been implemented succesfully in a thermal imager field test apparatus called the thermal imager performance indicator (TIPI) and may be implemented in current MRTD test equipment with little effort. (C) 1998 Society of Photo-Optical instrumentation Engineers.