Man drinking. Thermogram of a man drinking from a bottle, showing the variations in temperature. The temperature scale runs from red (warmest) through yellow and green to mauve (coldest). Thermography is a technique for visualising the temperature of surfaces by recording their emission of long-wavelength infrared radiation. This heat radiation is detected electronically and displayed with different colours representing different temperatures. In this case the temperature variations on the surface of the body and bottle of drink.