Vision is arguably the most important human sense. The processing and recording of visual data therefore has significant importance. The earliest images are from prehistoric drawings on cave walls or carved on stone monuments commonly associated with burial tombs. (It is not so much the medium that is important here – anything else would not have survived to today). Such images consist of a mixture of both pictorial and abstract representations. Improvements in technology enabled images to be recorded with more realism, such as paintings by the masters. Images recorded in this manner are indirect in the sense that the light intensity pattern is not used directly to produce the image. The development of chemical photography in the early 1800s enabled direct image recording. This trend has continued with electronic recording, first with analogue sensors, and subsequently with digital sensors, which include the analogue to digital (A/D) conversion on the sensor chip.
Imaging sensors have not been restricted to the portion of the electromagnetic spectrum visible to the human eye. Sensors have been developed to cover much of the electromagnetic spectrum from radio waves through to X-rays and gamma rays. Other imaging modalities have been developed, including ultrasound, and magnetic resonance imaging. In principle, any quantity that can be sensed can be used for imaging – even dust rays (Auer, 1982).
Since vision is such an important sense, the processing ...