EP0049388A2
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EP
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Video signal detector
Assignee: International Business Machines Corp
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Filing: 1981-09-16
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Granted: —
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Expires: 2001-09-16
Abstract
Abstract In an optical document reader a video signal detector is used to receive analog input signals (A) and to provide digital output signals (40, 70, F), said detector comprising a white level peak detector (C1, D3), a black level peak detector (C2, D1) and means (R2, R4, R8, R10) for combining the outputs from the white level and the black level peak detectors into a threshold signal (30, 60). Blocking means (D2) will prevent the black level peak detector to have an effect on the threshold signal when low contrast video signals are present. An output comparator (6) is used to compare a delayed video signal (E, 20, 50) with the threshold signal, whereby the delayed video signal is applied over a feedback resistor (R1) to the black peak detector. The combining means include control means (7, R10) for controlling the threshold signal level (a) and to compensate for displacement effects due to the optical components in the document reader.
Inventors
- 👤 Nils Gustaf Stälberg
Bibliographic Details
Application Number
—
Jurisdiction
EP
Data Source
google_patents
Last Synchronized
2026-10-28 03:51
CPC Classifications
G; G06; G06V; G06V30/00; G06V30/10; G06V30/16; G06V30/162
Claims Analysis
Total Claims: 12
Claim 1
Independent Claim
155 words
Video signal detector for detection of input analog video signals (A) from an optical document reader and for providing digital output signals (40, 70, F), comprising an input amplifier (5, 10, C3), a white level peak detector (Cl, D3) detecting the signal peak (B2) for such input video signals (Al-A6) which are provided by the document reader when a white area is scanned on the document, a black level peak detector (C2, Dl) detecting a video signal minimum value (B3) for black areas on the document, means (R2, R4, R8, R10) for combining the output signals from said both peak detectors into a threshold signal (30, 60) and an output comparator (6) comparing the threshold signal with a signal (E, 20, 50) representing the input video signal (A), characterized by means (D2) for preventing the black peak detector from having an effect on the threshold signal when input video signals are of low contrast type.
Claim 2
Dependent Claim
155 words
Video signal detector for detection of input analog video signals (A) from an optical document reader and for providing digital output signals (40, 70, F), comprising an input amplifier (5, 10, C3), a white level peak detector (Cl, D3) detecting the signal peak (B2) for such input video signals (Al-A6) which are provided by the document reader when a white area is scanned on the document, a black level peak detector (C2, Dl) detecting a video signal minimum value (B3) for black areas on the document, means (R2, R4, R8, R10) for combining the output signals from said both peak detectors into a threshold signal (30, 60) and an output comparator (6) comparing the threshold signal with a signal (E, 20, 50) representing the input video signal (A), characterized by means (D2) for preventing the black peak detector from having an effect on the threshold signal when input video signals are of low contrast type.
Claim 3
Dependent Claim
43 words
Video signal detector according to claim 1, characterized in that the preventing means (D2) connects the output (4) of the black level peak detector (C2, Dl) to the combining means (R2) when the signal level at this output falls below a given limit.
Claim 4
Dependent Claim
35 words
Video signal detector according to claim 2, characterized in that the preventing means is a diode (D2) and in that the given limit is defined by the voltage level at which the diode becomes conducting.
Claim 5
Dependent Claim
33 words
Video signal detector according to claim 1, characterized in that the input amplifier comprises an inverting integrator (5, C3) having a time controlled switch (10) connected over its input (R3) and output (11).
Claim 6
Dependent Claim
63 words
Video signal detector according to claim 1, characterized in that the white level peak detector comprises a diode (D3) and a condenser (Cl) that are connected in series, the input of this peak detector being connected to the output (11) of the input amplifier and its output (12) being connected through a further amplifier (3) to the combination means (R2, R4, R8, R10).
Claim 7
Dependent Claim
54 words
Video signal detector according to claims 1 and 2, characterized in that the black level peak detector comprises a condenser (C2) and a diode (Dl) that are connected in series, the input (15) of this peak detector being connected through a test and hold circuit (19) to the output (11) of the input amplifier.
Claim 8
Dependent Claim
37 words
Video signal detector according to claim 6, characterized in that the input (15) of the black level peak detector is connected through a delay circuit (8) to the video signal input (18) of the output comparator (6).
Claim 9
Dependent Claim
57 words
Video signal detector according to claim 7, characterized in that the common node (14) of the diode (Dl) and the condenser (C2) of the black level peak detector is connected through a resistor (Rl) to the video signal input (18) of the output comparator as well as through a further amplifier (4) to the combination means (R2).
Claim 10
Dependent Claim
52 words
Video signal detector according to claim 1, characterized in that the combination means (R2, R4, R8, R10) comprises control means (R2) in order to control the black level peak detector share and the white level peak detector share of the threshold signal at the threshold signal input (17) of the comparator (6).
Claim 11
Dependent Claim
44 words
Video signal detector according to claim 9, characterized in that the combination means comprises control means (7, R10) in order to control the threshold signal level (a) and to compensate the influence on the theshold level of the optical components of the document reader.
Claim 12
Dependent Claim
30 words
Video signal detector according to anyone of the claims 1-10, characterized by a feedback (12) for the output comparator (6) in order to lock the output signal (F, 40, 70).
References Cited (Backward Citations)
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