Television display utilizing local area brightness control

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. The window is moved one element over and a second computation is made which in turn results in a new bias being set for a second element centrally located within the second window. The window is slid one element at a time and a bias adjustment is made for each centrally located element until all of the elements in the first eight lines have been entered into the computation. The window is then deflected one line down and back to the first eight elements of the second through ninth display lines. The process of sliding the window to the right continues again until all the elements within this second set of sliding windows is completed. Thus, the window slides across the display one element at a time and down one line at a time at the end of each set of lines until all of the elements in the display have entered into the computation.