Local area contrast enhancement device
AssigneeHoneywell Inc.
InventorsRobert C. Fitch, Patrenahalli M. Narendra
Life of this patent
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Abstract
A local area contrast enhancement scheme for a video display includes a two dimensional recursive filter to obtain a moving average of the intensity variations in all areas of the display. This moving average is subtracted from the original signal to produce a signal which contains only local variations and this latter signal is expanded to increase the display contrast. The local area contrast enhancement scheme allows low contrast details to be perceived and permits hands-off operation of the display under varying scene conditions. The recursive filter approach results in a simple implementation of the enhancement scheme with both analog and digital circuitry.
Claims8
A system for providing local area contrast enhancement of an input signal comprising two dimensional recursive filter means connected to receive the input signal for producing a running average of the input signal, first means connected to receive the input signal and connected to said recursive filter means to receive the running average for subtracting the running average from the input signal to produce a subtracted signal, second means connected to said first means to receive the subtracted signal for amplifying the subtracted signal by an amount which varies with the running average to produce an amplified signal and third means connected to said second means to receive the amplified signal and connected to said first means to receive the running average for adding a portion of the running average to the amplified signal to produce an enhanced signal.
Apparatus for providing local area contrast enhancement of a vidicon signal which contains fluctuations indicative of a scene containing a target in a background comprising in combination:
- a first recursive filter having an input connected to receive the vidicon signal and operable to produce a first output signal indicative of the running average of the vidicon signal fluctuations;
- first summing means having a first input connected to receive the vidicon signal, having a second input connected to the first recursive filter to receive the first output signal and operable to produce a first sum signal indicative of the difference between the vidicon signal and the summing average of the vidicon signal;
- an absolute value circuit having a first input connected to receive the vidicon signal, having a second input connected to said first recursive filter to receive the first output signal and operable to produce a second sum signal indicative of the absolute difference between the vidicon signal and the running average of the vidicon signal;
- a second recursive filter having an input connected to said absolute value circuit to receive the second sum signal and operable to produce a second output signal indicative of the running average of the second sum signal;
- variable gain means having a first input connected to said first summing means to receive the first sum signal, having a second input connected to said second recursive filter to receive the second output signal and operable to produce a modified output signal indicative of the first sum signal amplified by an amount dependent upon the magnitude of the second output signal;
- and
- second summing means having a first input connected to said variable gain means to receive the modified output signal, having a second input connected to said first recursive filter to receive the first output signal and operable to produce a resultant signal indicative of the sum of the modified output signal and a portion of the running average of the vidicon signal.
Dependencies are inferred from the claim text.