Thermogram of the head and upper torso of a naked man. Thermography is an imaging technique for mapping the heat distribution over the surface of a body. Here, the colour-coded image shows temperature variation in 0.1 degree celsius steps, from blue, for the coldests, through green, pink, red, orange and yellow, for the hottest areas. Thermography has proved useful in manufacturing and medicine (where it may reveal disorders such as tumours and arthritis). It was developed by the military in the 1970's and 1980's to assist night vision; the solid state sensors used in the thermograph can detect infra-red radiation even in darkness and/or smoke.