Multiband Photography

A special type of photography wherein an object is photographed simultaneously in at least two regions of the spectrum in order to reveal or enhance differences in detail that are not captured in ordinary photography with visible light. In selecting the spectral regions to be used, the optical characteristics of the object and the reasons for which it is being photographed are taken into account. In some cases, pictures may have to be taken in both the visible and invisible parts of the spectrum. In other cases, selected narrow regions of the visible spectrum may be used. Both black-and-white and color photographic films are employed in multiband photography.

Black-and-white films may be used to obtain color-separation images in several regions of the spectrum, including the region where the contrast between the details being studied and their background is maximal. The separate negatives produced may be lined up and viewed directly or, in a discriminating study, through appropriate filters in a chromoscope.

When color films are used, the color-separation images are lined up from the moment they are formed, since in this case special two- or three-layer multiband films are used. (Three-layer films contain an infrared-sensitive layer.) When the photograph is taken, these materials do not record the entire spectrum of the light reflected by the object. Instead, they record only individual regions of the reflected light. The colors of the object are therefore distorted. It is precisely these distortions, however, that permit the details under study to be seen.

Multiband photography is employed in the aerial photography of objects in nature, such as crops, forests, and soils. Multiband photography plays an important role in photographing the surface of the earth and planets from spacecraft and artificial earth satellites (seeSPACE PHOTOGRAPHY). In addition, the multiband technique has come into use in the photomicrography of biological specimens and microsections of minerals that contain inclusions. Studies are being carried out on the feasibility of multiband photography with X rays when conventional three-layer color photographic films are used. Here, the color differences in the image correspond to the different depths to which the radiation penetrates (through one, two, or three emulsion layers) and, consequently, to the different degrees to which the radiation is attenuated by the object.