| 摘要 |
An iterative real time histogram modification system for use in image processing, such as image contrast enhancement of for example scenes, radiograms and thermograms. In the described system input analogue video signals to be modified are digitized and applied to an encoding module including a code RAM which compresses the input grey levels into a lesser number of output grey levels in accordance with a recoding strategy applied to the code RAM. The recoding strategy is determined iteratively using a predetermined scene adaptive operator. This is done by forming a histogram of the pixels in the respective output grey levels. Thereafter the count in each grey level is compared with a predetermined population figure for that grey level and if the difference between the count and population figure is outside an acceptable range, termed a window, then the recoding strategy to be used during the next frame of the input signals is altered so that the number of input grey levels compressed into the particular output grey level is adjusted appropriately. The recoding strategy may be applied to a local area of the frame, which area is selected at will, or to the entire frame in which case the histogram is formed from a subset of all the pixels. The scene adaptive operators include histogram equalization, Gaussian distribution, hyperbolic and exponential. By using a suitably programmed microprocessor different scene adaptive operators may be selected at will and a "zoom" facility may be provided in which the size of the local area is varied and corresponding changes are made to the window and set of population figures.
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