Resolution

The deflection of the incident light beam by the test medium is measured on the color filter during the color schlieren measurements. The image of the filter is recorded with a certain number of pixels in two directions and is digitized over the RGB scale of (8-bit). The hue-displacement information is contained in the calibration curve where the hue is plotted as a function of the spot position. The quality of the calibration curve depends on the pixel size, the color scale, the micrometer used for vertical movement of the filter, and the spot sized attained after decollimation.

The sensitivity of color schlieren measurements is generally quite high and is adjustable by proper selection of the optical components and design of the color filter. Equation 3 shows that the deflection of the light beam is proportional to L, the length of the test section in the direction of propagation of light and , the focal length of the decollimating lens. Thus, large values of and can be used to detect small gradients in temperature and concentration. The measuring range of the color schlieren is the maximum deflection angle at which linear range of color indicator i.e. hue value is achieved. It is defined as:

(6)

where b_f and b_s are the dimensions of the color filter and the source respectively. In the present case, = 2.6 mm, = 0.23 mm and =750 mm, returning mrad. For the 8-bit color camera, the theoretical sensitivity is of the full range. When the filter is at the central position corresponding to the zero beam deflection, the deflection can be measured in the interval mrad. Thus, the dynamic range is equal to 128 with minimum detectable deflection angle of 0.012 mrad.

The sensitivity of the color schlieren technique is inversely proportional to the range and therefore the color filter can be designed for required resolution. The sensitivity also depends on the change in refractive index with respect to temperature and concentration. In terms of temperature, this derivative in air and in water. Clearly, sensitive measurements can be carried out in water since it has a higher sensitivity compared to air, by around two orders of magnitude.