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Analog Video Detector Based on Multilevel Contrast Comparisons

IP.com Disclosure Number: IPCOM000077261D
Original Publication Date: 1972-Jul-01
Included in the Prior Art Database: 2005-Feb-25
Document File: 2 page(s) / 42K

Publishing Venue

IBM

Related People

Chang, DC: AUTHOR

Abstract

The circuit of Fig. 1, for converting analog video to two-level video, tolerates appreciable noise, or variation of background level in the analog video.

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Analog Video Detector Based on Multilevel Contrast Comparisons

The circuit of Fig. 1, for converting analog video to two-level video, tolerates appreciable noise, or variation of background level in the analog video.

Threshold comparator circuits C1, C2, C3 compare the video input (2.0) to respective black level references CL1, CL2, CL3 and produce respective outputs, illustrated in Fig. 2, when the video "blackness" exceeds the respective reference levels.

Negatively triggered latches L2, L3 are set and reset by particular sequences of outputs of the comparator circuits. L2 is set (output 2.4 "up") by negative transitions of the complement of output 2.2 of C2, the latter provided by inverter I2. L2 is reset by negative transition of output 2.1 of C1. L3 is set (2.5 "up") by negative transitions of the complement of 2.3 of C3, provided by inverter I3. L3 is reset by negative transitions of output 2.2 of C2.

The function of the higher threshold channels is to capture weak white details, such as between t5 and t6, in a basically black detection system, by looking for white not with respect to CL1, but with respect to CL2 or CL3 as the background changes.

The white levels of all channels are "OR'ed" by the "-0" circuit, resulting in the output of 2.8.

Sensitivity to directional change is controlled by the difference between on and off levels of each of the comparators C1 through C3. Greater resolution or independence from background variation is achieved by increasi...