Infrared scanner using dynamic range conserving video processing
First Claim
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1. A method for decreasing the dynamic range of a scene video signal for processing said signal in a channel of limited dynamic range comprising the steps of:
- including in the scene video signal at the point of origin thereof a pair of reference signals of predetermined video intensity difference,separating the transient alternating current component of the video signal from the direct current reference component;
discarding the direct current reference component;
adding a first new direct current reference component signal to said transient alternating current component during the signal time portions corresponding to said reference signals;
adding a second new direct current reference component signal to said transient alternating current component during the signal time portions corresponding to scene video;
whereby the overall dynamic range of the processed video signal from said adding of first and second new reference component signals is of limited amplitude.
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Abstract
A video scanning and signal processing arrangement usable with devices such as a forward looking infrared system. The signal processing disclosed employs an analog-to-digital converter of limited dynamic range and incorporates plural closed loop signal modifying for optimizing the use of this limited dynamic range.
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Citations
21 Claims
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1. A method for decreasing the dynamic range of a scene video signal for processing said signal in a channel of limited dynamic range comprising the steps of:
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including in the scene video signal at the point of origin thereof a pair of reference signals of predetermined video intensity difference, separating the transient alternating current component of the video signal from the direct current reference component; discarding the direct current reference component; adding a first new direct current reference component signal to said transient alternating current component during the signal time portions corresponding to said reference signals; adding a second new direct current reference component signal to said transient alternating current component during the signal time portions corresponding to scene video; whereby the overall dynamic range of the processed video signal from said adding of first and second new reference component signals is of limited amplitude. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8)
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9. Apparatus for processing infrared scene video signals of wide dynamic range comprising:
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N channel scanning means for generating N electrical signals each representing sequential video pixels of said infrared scene taken along a plurality of adjacent scanning paths; reference signal generating means including a pair of reference infrared sources of predetermined temperature difference and located near an end of said scanning paths for incorporating in each of said N video signals a pair of electrical signals representing a predetermined temperature difference; video amplifier means including N AC coupled amplifiers for amplifying and extracting the transient AC component signal from each of said N electrical signals; automatic gain control means responsive to said reference signal amplitude difference for equalizing the channel gains in said N channel scanning means; means for adding a first new direct current reference signal to each of said transient AC component signals during the time interval corresponding to said reference signal pair therein; means for adding a second new direct current reference signal to each of said transient AC component signals during the time interval corresponding to said scene video signals, said AC component signal with said added first and second new reference signals comprising a reconstituted signal; signal multiplexer means for arranging samples of said N signals into an ordered serial signal; analog-to-digital converter means for converting said ordered serial signal into a sequence of digital signals whereby the dynamic range required of said analog-to-digital converter can be substantially reduced with the selection of appropriate values for said first and second direct current reference signals. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
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20. DC restorer apparatus for processing a scene video signal of wide dynamic range using components of lesser dynamic range comprising:
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reference video means for including in the scene video signal a pair of reference signals of predetermined video intensity difference; AC coupling means for separating the alternating current component of the video signal from the direct current reference component and for discarding the direct current reference component; means for generating and adding to said transient alternating current component signal a first new direct current reference component signal during the signal time interval corresponding to said reference signals; means for generating and adding to said transient alternating component signal a second new direct current reference component signal during the time interval corresponding to scene video; whereby large amplitude DC components of said scene and reference composite video signal may be replaced with DC components of smaller preferable magnitude.
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21. Electronic scanning apparatus comprising:
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a plurality of transducer elements each capable of producing a video signal electrical output representing successive pixels of an aperture framed input scene scanned along predetermined sampling paths traversing said aperture; a pair of uniform intensity reference signal sources located adjacent said aperture and scanned sequentially by said transducer elements near one end of each of said sampling paths, said reference sources being maintained at a predetermined intensity difference; gain controllable AC coupled channel signal amplifier means including an amplifier coupled with each of said transducer elements for removing the DC reference component and controllably amplifying the AC transient component of each transducer element video signal; multiplex channel commutating means for sampling said plurality of transducer element amplified video signals and generating an output signal comprised of segments sequentially taken therefrom; DC coupled signal amplifier means including a gain control input and a DC level control input for generating from said multiplexer signal a newly DC referenced scanning output signal; first loop automatic gain control means connected with said scanning output signal and said gain control input of said DC coupled signal amplifier means and responding to reference source intensity difference components in said output signal, for gain adjusting said DC coupled signal amplifier means in compensation for transducer element differences; second loop level control means connected with said scanning output signal and said DC level control input of said DC coupled signal amplifier means for generating a first level control signal complementary to the overall average intensity of said reference signal sources for each said transducer and a second level control signal biased with respect to said first level control signal t be complementary to the scene sampling path average intensity for all transducer elements, for relating said scanning output signal to a common reference for said multiplexed channels; third loop automatic gain control means connected with said scanning output signal and said AC coupled signal amplifier means and responding to scene contrast data for controlling the gain of said AC coupled amplifier and the image contrast in the output signal of said amplifier.
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Specification