are vacuum phototubes that amplify light by accelerating the photoelectrons to knock more electrons free from a series of electrodes. They are among the most sensitive light detectors but are not well suited to photography. Aliasing Aliasing can occur in optical and chemical processing, but it is more common and easily understood in digital processing. It occurs whenever an optical or digital image is sampled or re-sampled at a rate which is too low for its resolution. Some digital cameras and scanners have anti-aliasing filters to reduce aliasing by intentionally blurring the image to match the sampling rate. It is common for film developing equipment used to make prints of different sizes to increase the graininess of the smaller size prints by aliasing. It is usually desirable to suppress both noises such as grain and details of the real object that are too small to be represented at the sampling rate. See also Astrophotography Underwater photography Infrared photography Ultraviolet photography Silver bromide Photographic processing Image editing Highlight headroom References Photography, science of Photography