As the liquid crystal passes through its active range of colors (blue to red), images are acquired for every 0.2^oC drop in the surface temperature. Simultaneously, wall temperatures from thermocouples are recorded using the data acquisition card, NI-4351 (National Instruments). Subsequently the series of images are digitized, and the hue information (in fact, hue, saturation, and intensity) is extracted for a sample region of 50 × 50 pixels, corresponding to an area of 25 × 25 mm² . The sample region (Figure 6.4(b)) is selected in such a manner that there is a thermocouple that lies centrally underneath.

Figure 6.4(b): Using a small patch of area for hue calculation