Hughes Aircraft Company

David J Ketcham

Eugene W Opittek

Michael D Pruznick

Roger W Lowe

Edward J Dragavon

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.

Television display utilizing local area brightness control

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. The area being equalized for each window position may be selected equal horizontally and vertically to the respective amount of shifting along each segment between window positions and of the shifting of the window between adjacent segments. In order to process the histograms at the video rate and resolution the system computes mini or subhistograms from an area formed of a selected number of elements of the histogram in the horizontal dimension by the number of histogram lines in the vertical dimension of the window and sums the statistics of a selected number of the mini histograms to generate one histogram for equalizing the central area. In the continuous process the mini histograms are read out in parallel to form a plurality of histograms and multiple truncation maps which are stored in a selected number of RAM memories. Digital video is then processed through these transformed memories and stored in output buffers which may be required because of the multiplexing. In the system utilizing one dimensional processing, histograms are formed for the data of a selected number of lines in order to equalize the data of a selected line or lines and the histogram window area is moved vertically over the entire raster area.

Raster display histogram equalization

A histogram equalization system that adaptively redistributes the intensity coding of the video in order to provide an equal number of elements at all display intensity levels. The actual amplitude value of the input video as stored in an integrator, for example, is utilized to address a random access memory which originally is loaded with all zeros. The memory is organized such that there are as many addressable words as there are possible video intensity values carried in the integrator thereby building up a histogram within the memory. Upon completion of the histogram, a constant equal to the number of picture elements corresponding to the data used to form the histogram divided by the number of values to which it is desired to truncate, is utilized in a comparator as the histogram memory is sequentially read out and accumulated to determine the truncation points. A latching circuit is filled with the truncation point values and these points are used in a truncation logic circuit responding to the input video signal to reduce the number of video bits. The truncated signal increases the sensitivity to localized signal variations of a scene so as to increase the detail of the gray scale region requiring additional intensity codes.

Growing community of inventors

Lakewood, CA, United States of America

David J Ketcham