Abstract: A raster display system is disclosed which utilizes a "sliding window" effect for enhancing the contrast of an image by adjusting the video gain and brightness within the window. The television display may have a raster having 512 lines and 512 elements per line. The display system utilizing digital circuitry calculates the average brightness of a "window" having a predetermined number of elements per display line and several parallel display lines, such as, for example, eight lines and eight elements per line. Thus, an eight-by-eight window is presented. The average brightness of the window is subtracted from the brightness of a centrally located element which results in the relative brightness of the element. This relative brightness signal is multiplied by a gain factor and the product is applied to an output circuit for controlling the bias of a central element of the window.

Abstract: Real time histogram equalization systems for a television type display that performs equalization with one or two dimensional processing on a local area or sliding window basis. For the two dimensional system, the intensity for any particular point in the image is adjusted according to a histogram of the area contained within a window immediately surrounding the point to be equalized. The histogram forming window provided by the system moves across the image in two dimensions both horizontally along each of a plurality of overlapping segments arranged parallel in the vertical dimension, and at each window position reassigned center picture elements are equalized. The processing of the histograms area or the sliding process is continued over the entire surface of the raster with the process being then repeated in a continuous fashion.