US3845242A
Expired / Lapsed
US
⏱️ 0.0 years remaining
Video signal processing system for facsimile transmission
Assignee: 3M Co
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Filing: 1972-11-21
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Granted: 1974-10-29
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Expires: 1992-11-21
Abstract
Abstract A facsimile transceiver for use with telephone line networks in which the original image is photoelectrically scanned to produce a video baseband signal, the baseband signal is shaped by a nonlinear transfer network and converted into a relatively high frequency period-modulated signal, whose carrier frequency is outside the passband of the telephone transmission link and, after frequency division to a frequency within the passband, the low frequency components of the resultant carrier signal are emphasized. In addition, the signal is pre-equalized to partially compensate for the delay and amplitude characteristics of the voice-grade telephone line transmission facilities which carry the period-modulated signal to a receiving station transceiver. The non-linear circuit which shapes the video baseband signal adapts to the changing character of the video signal being sent, providing improved gray-scale reproduction of the facsimile copy while enhancing the resolution of detailed image segments through variable emphasis of the high frequency components of the baseband signal. In the receiver section of the transceiver, the incoming signal is de-emphasized and post-equalized for correction of delay characteristics of the telephone line transmission link after which the upper sideband is removed, and the resulting signal, which possesses a substantial A.M. content is passed through a first hard-limiter which in effect produces a double sideband carrier signal which is then post-equalized for correction of the amplitude characteristics of the telephone line transmission link whereupon the signal is again hard-limited before being passed to a period-to-amplitude demodulator whose output, after further amplification, shaping and emphasis, drives a stylus to produce a faithful replica or facsimile of the original image.
Inventors
- 👤 W Richeson
- 👤 R Dreisbach
Bibliographic Details
Application Number
—
Jurisdiction
US
Data Source
google_patents
Last Synchronized
2026-11-03 13:57
CPC Classifications
H; H04; H04N; H04N1/00; H04N1/00095
Claims Analysis
Total Claims: 15
Claim 1
Independent Claim
148 words
In combination, means for converting image information into a time-varying electrical baseband signal, a non-linear transfer network for reshaping the waveform of said baseband signal to produce a modulating signal having limits between a first signal level representing black and a second signal level representing white, said network including means for increasingly shifting the short-term average level of said modulating signal toward said first level and away from said second level with increasing baseband signal frequency; means for translating said modulating signal into a message signal having an instantaneous frequency which varies between an upper frequency when said modulating signal is at said first level, to a lower frequency when said modulating signal is at said second level; means for transmitting said message signal over a communication channel to a receiving station; and means at said receiving station responsive to said message signal for reproducing said image information.
Claim 2
Dependent Claim
148 words
In combination, means for converting image information into a time-varying electrical baseband signal, a non-linear transfer network for reshaping the waveform of said baseband signal to produce a modulating signal having limits between a first signal level representing black and a second signal level representing white, said network including means for increasingly shifting the short-term average level of said modulating signal toward said first level and away from said second level with increasing baseband signal frequency; means for translating said modulating signal into a message signal having an instantaneous frequency which varies between an upper frequency when said modulating signal is at said first level, to a lower frequency when said modulating signal is at said second level; means for transmitting said message signal over a communication channel to a receiving station; and means at said receiving station responsive to said message signal for reproducing said image information.
Claim 3
Dependent Claim
112 words
An arrangement as set forth in claim 1 in which said means for converting image information into a time-varying baseband signal comprises, in combination, photoelectric means at said sending station for scanning an image composed of light and dark areas to produce a time-varying scan signal in which light areas are represented by signal levels of greater magnitude and dark areas by signal levels of lesser magnitude, and means for forming the sum of said scan signal and a constant-level signal of opposite polarity to form said baseband signal in which dark areas are represented by signal levels of greater magnitude and light areas are represented by signal levels of lesser magnitude.
Claim 4
Dependent Claim
63 words
An arrangement as set forth in claim 1 wherein said means for increasingly shifting the short term average level of said modulating signal with increasing frequency comprises, in combination, a capacitor serially connected with a non-linear impedance element, the impedance presented by said capacitor decreasing with increasing modulating signal frequency and the impedance of said non-linear element decreasing and increasing modulating signal amplitude.
Claim 5
Dependent Claim
24 words
An arrangement as set forth in claim 3 including at least one diode for providing a low-impedance path through which said capacitor can discharge.
Claim 6
Dependent Claim
147 words
In combination, a source of a time-varying baseband signal; a controlled signal generator responsive to said baseband signal for producing a message signal having a frequency related to the amplitude of said baseband signal, said message signal comprising carrier and sideband frequency components; a channel having a predetermined passband for transmitting said message signal from a sending to a receiving station; and means for shifting the effective carrier frequency of said message signal with respect to the passband of said channel to increase the proportion of said passband available for one sideband of said message signals whenever substantial high-frequency components appear in said baseband signal, said means for shifting the carrier frequency comprising a non-linear network interposed between said source of baseband signals and said controlled signal generator for altering the waveshape of the signal from said source to shift The average value of said baseband signal.
Claim 7
Dependent Claim
147 words
In combination, a source of a time-varying baseband signal; a controlled signal generator responsive to said baseband signal for producing a message signal having a frequency related to the amplitude of said baseband signal, said message signal comprising carrier and sideband frequency components; a channel having a predetermined passband for transmitting said message signal from a sending to a receiving station; and means for shifting the effective carrier frequency of said message signal with respect to the passband of said channel to increase the proportion of said passband available for one sideband of said message signals whenever substantial high-frequency components appear in said baseband signal, said means for shifting the carrier frequency comprising a non-linear network interposed between said source of baseband signals and said controlled signal generator for altering the waveshape of the signal from said source to shift The average value of said baseband signal.
Claim 8
Dependent Claim
108 words
An arrangement as set forth in claim 5 in which said source of a time-varying baseband signal comprises, in combination, photoelectric means at said sending station for scanning an image composed of light and dark areas to produce a time-varying scan signal in which light areas are represented by signals levels of greater magnitude and dark areas by signal levels of lesser magnitude, and means for forming the sum of said scan signal and a constant-level signal of opposite polarity to form said baseband signal in which dark areas are represented by signal levels of greater magnitude and light areas are represented by signal levels of lesser magnitude.
Claim 9
Dependent Claim
192 words
An arrangement for transmitting an image from a sending to a receiving station comprising, in combination, means for scanning said image to produce a time-varying electrical baseband signal characterized in that black image areas are represented by a first signal level, white by a second signal level, and the intermediate black-to-white gray-scale by the scale of signal levels bounded by said first and second levels; first signal reshaping means at said sending station for preferentially amplifying low-frequency baseband signal variations near said first signal level in comparison to like variations near said second signal level; second signal reshaping means at said sending station for shifting the short-term average value of said baseband signal toward said first level whenever said baseband signal contains substantial high-frequency components; means for converting said baseband signal, as modified by said first and second reshaping means, into a cyclical message signal having an instantaneous frequency related to the magnitude of said modified baseband signal; a band-limited communication channel for transmitting said message signal from said sending station to said receiving station; and means at said receiving station for converting said message signal into a replica of said image.
Claim 10
Dependent Claim
192 words
An arrangement for transmitting an image from a sending to a receiving station comprising, in combination, means for scanning said image to produce a time-varying electrical baseband signal characterized in that black image areas are represented by a first signal level, white by a second signal level, and the intermediate black-to-white gray-scale by the scale of signal levels bounded by said first and second levels; first signal reshaping means at said sending station for preferentially amplifying low-frequency baseband signal variations near said first signal level in comparison to like variations near said second signal level; second signal reshaping means at said sending station for shifting the short-term average value of said baseband signal toward said first level whenever said baseband signal contains substantial high-frequency components; means for converting said baseband signal, as modified by said first and second reshaping means, into a cyclical message signal having an instantaneous frequency related to the magnitude of said modified baseband signal; a band-limited communication channel for transmitting said message signal from said sending station to said receiving station; and means at said receiving station for converting said message signal into a replica of said image.
Claim 11
Dependent Claim
142 words
In a facsimile system, a circuit for reshaping the waveform of a time-varying signal representing white by a first signal amplitude level, black by a second signal amplitude level, and the white-to-black gray-scale by amplitudes within the range bounded by said first and second levels, said circuit comprising, in combination, an amplifier having an input and an output, a negative feedback network connected between said input and said output, said network including a first non-linear impedance element for reducing the amount of negative feedback as the amplitude of said signal approaches said second amplitude level and a second non-linear impedance element serially connected with a capacitor for reducing the amount of negative feedback for higher frequency signal variations greater than a predetermined intensity, and clamping means for limiting said signal to amplitudes within a range bounded by said first and second levels.
Claim 12
Dependent Claim
142 words
In a facsimile system, a circuit for reshaping the waveform of a time-varying signal representing white by a first signal amplitude level, black by a second signal amplitude level, and the white-to-black gray-scale by amplitudes within the range bounded by said first and second levels, said circuit comprising, in combination, an amplifier having an input and an output, a negative feedback network connected between said input and said output, said network including a first non-linear impedance element for reducing the amount of negative feedback as the amplitude of said signal approaches said second amplitude level and a second non-linear impedance element serially connected with a capacitor for reducing the amount of negative feedback for higher frequency signal variations greater than a predetermined intensity, and clamping means for limiting said signal to amplitudes within a range bounded by said first and second levels.
Claim 13
Dependent Claim
23 words
A circuit as set forth in claim 8 including at least one diode connected to provide a low-impedance discharge path for said capacitor.
Claim 14
Dependent Claim
106 words
In a fascimile transceiver capable of operation in both sending and receiving modes, a stylus driving network comprising, in combination, a demodulator for producing a stylus-driving signal in which white is represented by substantially zero signal amplitude and black is represented by a signal of substantial magnitude having a first polarity, and a logic circuit for applying a signal of opposite polarity to said stylus to retract said stylus whenever said transceiver is operating in said sending mode and to further retract said stylus when said transceiver is operating in said receiving mode for predetermined periods preceding and following the appearance of said stylus driving signal.
Claim 15
Dependent Claim
106 words
In a fascimile transceiver capable of operation in both sending and receiving modes, a stylus driving network comprising, in combination, a demodulator for producing a stylus-driving signal in which white is represented by substantially zero signal amplitude and black is represented by a signal of substantial magnitude having a first polarity, and a logic circuit for applying a signal of opposite polarity to said stylus to retract said stylus whenever said transceiver is operating in said sending mode and to further retract said stylus when said transceiver is operating in said receiving mode for predetermined periods preceding and following the appearance of said stylus driving signal.
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USPTO Annuity & Maintenance Windows
| Annuity Stage | Window Opens | Payment Deadline | Surcharge Period Until | Estimated Fee | Status |
|---|---|---|---|---|---|
| 3.5 Years (Year 4) | 1977-10-28 | 1978-04-29 | 1978-10-29 | $2000.00 | Window Closed / Lapsed |
| 7.5 Years (Year 8) | 1981-10-28 | 1982-04-29 | 1982-10-29 | $3760.00 | Window Closed / Lapsed |
| 11.5 Years (Year 12) | 1985-10-28 | 1986-04-29 | 1986-10-29 | $7700.00 | Window Closed / Lapsed |