This kind of special images are usually photo-like prints or computer monitor displays produced from input data representing segments or intervals of the electromagnetic spectrum. A significant advance in sensor technology stemmed from subdividing spectral ranges of radiation into bands (intervals of continuous wavelengths), allowing sensors in several bands to form multispectral images. This concept should be familiar to anyone who has used color filters on a photo-camera. The first multispectral photography from space happened during the famous 1968 Apollo 9 mission. Scientist mounted four Hasselblad cameras in a holder such that they all aimed at the same target point when an astronaut triggered their shutters simultaneously. The astronauts took in the green, red, photo IR bands, and a (false) color IR picture. Skylab later used a six camera array.