Histogram-based intensity expansion

Abstract

A method and apparatus for selectively scaling portions of image data based on the intensity levels of historical image data. The selective scaling, or level expansion, provides improved images by increasing or decreasing the intensity of a portion of image pixels. Black level expansion reduces the intensity of dark pixels and is appropriate when a relatively large number of the image pixels have a high intensity level. White level expansion increases the intensity of bright pixels and is appropriate when a relatively large number of image pixels have a low intensity level. Level expansion is implemented by using histogram comparators to compare the intensity of each pixel with a threshold, typically on a frame-by-frame basis. When an adequate number of pixels in each frame meet the threshold criteria, the level expansion is increased. Field accumulator is used to determine whether and by how much the image data is scaled. Field accumulator increments each time a frame meets the expansion criteria, as determined by the histogram comparators , and decrements each time a frame does not meet the expansion criteria. The value accumulated by the field accumulator is used by level expander to scale at least a portion of the input data.