Supermarket. Thermogram of a woman pushing a shopping trolley in a supermarket. The image shows variation in temperature. The temperature scale runs from red (warmest) through yellow, green, cyan and blue to mauve (coldest). Thermography is a technique for visualising the temperature of surfaces by recording the emission of long-wavelength infrared radiation. This heat radiation is detected electronically and displayed with different colours representing different temperatures. The contrast of the warm body temperature of the shopper and the cold freezer compartments (blue and mauve) is clearly shown here.