Contrast Enhancement Techniques Study. Phase III.

摘要

The development of a real-time TV compatible contrast enhancement unit was conducted. This development was the result of a three phase study program to evolve and evaluate, by computer simulation, alternate contrast enhancement techniques. The three techniques studied were the Local Area Histogram Equalization (LAHE), Local Area Brightness and Gain Control (LABGC), and Haar Transform Filtering (HTF). The three techniques studied were the Local Area Histogram Equalization (LAHE), Local Area Brightness and Gain Control (LABGC), and Haar Transform Filtering (HTF). The LABGC technique was selected for hardware implementation due to its relative simplicity and simulated performance. The LABGC algorithm basically operates on and adjusts the gain and bias of a single pixel element as a function of the statistics of immediate surrounding pixels. If there is a wide variation in the values (high contrast) no gain is applied; conversely, high gain is applied when the immediate area exhibits small variations (low contrast). During the first part of this project, a design study was conducted using the computer simulation model to optimize the mechanization parameters. In particular, the pixel area size of 4 x 4 pixels was selected, the video is digitized to 6 bits and multiple gain transfer functions were selected. An all digital mechanization was selected in order to eliminate analog noise and nonlinearity problems.