A majority of researchers recommend the in-situ mode of calibration. Here, calibration is carried out within the main experimental apparatus itself. A wide-band calibration technique (covering the bandwidth of the liquid crystal material) applied point-wise is proposed. Wide-band calibration employed by the previous researchers mostly calibrate the LCs using a single reference point on the test surface against temperature, and then apply this single-point calibration over the entire test surface (Smith, 2001). The illumination (source) as well as imaging (camera) positions is close to normal with respect to the test surface. For the micro-encapsulated thermochromic LCs, the sensitivity of hue to the viewing and illumination angles is found to be insignificant (Camci, 1992, 1993).

It is worth mentioning here that recent studies have opted for pixel-level calibration- namely generate calibration curves of hue vs temperature for each of the 1024 X 1024 pixels.

For the images discussed in the present chapter, an in-situ , single-point calibration has been performed under no-flow condition. The lighting arrangement and camera position are kept identical for the calibration stage and the full experiment. The parameters of the image processing system including color capturing settings are locked. The imaging camera is mounted at the top of the test section. The illumination system was also located on the camera side of the test surface (called on-axis lighting). With this configuration, the maximum permissible deviations of the viewing inclination and illumination angle from the normal are found to be less than 10^o and 20^o respectively.