Showing papers on "Histogram equalization published in 1975"

Histogram equalization system for display improvement

Abstract: 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.

Raster display histogram equalization

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. 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.

Gray-level transformations for interactive image enhancement.

Abstract: A gray-level transformation method suitable for interactive image enhancement was presented. It is shown that the well-known histogram equalization approach is a special case of this method. A technique for improving the uniformity of a histogram is also developed. Experimental results which illustrate the capabilities of both algorithms are described. Two proposals for implementing gray-level transformations in a real-time interactive image enhancement system are also presented.