Deemphasis and subsequent reemphasis of high-energy reversed-spectrum components of a folded video signal

• US 6,246,827 B1
• Filed: 07/08/1993
• Issued: 06/12/2001
• Est. Priority Date: 08/17/1990
• Status: Expired due to Fees

• Current Assignee: Samsung Electronics Co. Ltd.
• Original Assignee: Samsung Electronics Co. Ltd.
• Inventors: Limberg, Allen LeRoy, Yun, Jong Kyung, Wedam, Werner F., Schnitzler, Raymond, Ko, Jung Wan, Strolle, Christopher H., Weckenbrock, Hermann J.
• Primary Examiner(s): TRAN, THAI Q
• Application Number:
  US08/087,362
• Time in Patent Office: 2,896 Days
• Field of Search: H04/N.979, 358/310, 358/330, 348/571, 348/392, 348/427, 386/33, 386/109, 386/111, 386/112, 386/1
• US Class Current: 386/328
• CPC Class Codes: H04N 5/923 using preemphasis of the signal before modulation and deemphasis of the signal after demodulation volume compression or expansion in amplifiers in general H03G7/00
• CPC Class Codes: H04N 9/7976 by spectrum folding of the high frequency components of the luminance signal
• CPC Class Codes: H04N 9/80 Transformation of the television signal for recording, e.g. modulation, frequency changing; Inverse transformation for playback
• CPC Class Codes: H04N 9/8205 involving the multiplexing of an additional signal and the colour video signal
• CPC Class Codes: H04N 9/835 involving processing of the sound signal
• CPC Class Codes: H04N 9/898 using frequency multiplication of the reproduced colour signal carrier with another auxiliary reproduced signal, e.g. a pilot signal carrier H04N9/83 takes precedence

Abstract

A system for reproducing a luminance signal from a medium containing a previously recorded luminance signal with a high-frequency portion thereof compressed in dynamic range includes a circuit for recovering that luminance signal from the medium. Filtering is done to separate the low-frequency and compressed-in-dynamic-range high-frequency portions of the recovered luminance signal from each other. A corer responds to the separated compressed-in-dynamic-range high-frequency portion of the recovered luminance signal to provide a cored high-frequency portion with expanded dynamic range and reduced noise. The level of the cored high-frequency portion with expanded dynamic range and reduced noise is then boosted by a predetermined amount to compensate for energy losses during the compression of the dynamic range and added back to the low-frequency portion of the recovered luminance signal to reproduce a full-band luminance signal with at least partially restored dynamic range for high-frequencies and without readily visible high-frequency noise.

Claims

1. Apparatus for reversing the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan line rate, said apparatus comprising:

a source of said video signal having a lower video frequency portion and an upper video frequency portion;

a generator of a carrier signal of a carrier frequency that is a multiple of said prescribed scan line rate and above said upper video frequency portion;

a multiplier having a multiplicand input terminal coupled to receive one of said video and carrier signals and a multiplier input terminal coupled to receive another of said video and carrier signals for generating a product signal having a first amplitude-modulation sideband that is lower in frequency than said carrier frequency and having a second amplitude-modulation sideband that is higher in frequency than said carrier frequency; and

means for reversing at said prescribed scan line rate the phase of the carrier signal received by said multiplier, each reversal being at a respective instant between successive scan lines, thereby enabling conversion of said product signal into a reversed-spectrum video signal with line-to-line inversion of phase.

2. Apparatus as set forth in claim 1, in combination with:

means for linearly combining said video signal with said reversed-spectrum video signal with line-to-line alternation of phase to generate a combined signal.

3. A combination as set forth in claim 2, wherein said means for linearly combining said video signal with said reversed-spectrum video signal with line-to-line alternation of phase essentially consists of:

an adder connected for receiving said video signal as a first summand input signal, for receiving said reversed-spectrum video signal with line-to-line alternation as a second summand input signal, and for supplying said combined signal as a sum output signal.

4. Apparatus as set forth in claim 1, further comprising:

means for lowpass filtering said combined signal, having a bandwidth that extends only to a frequency that is not higher than said carrier frequency.

5. Apparatus as set forth in claim 1, further comprising:

means for lowpass filtering said combined signal, having a bandwidth that extends only to a frequency that is not substantially higher than one half said carrier frequency.

6. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan line rate, said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier signal of a carrier frequency that is a multiple of said prescribed scan line rate and above said upper video frequency;

means for reversing the phase of the carrier signal at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier signal;

a highpass filter responsive to said video signal for supplying a high band video signal;

means for detecting the level of energy in said high band video signal, thereby to generate a detected energy signal;

means responsive to said detected energy signal exceeding a prescribed threshold level, for generating a gain control signal that is of maximum value until said prescribed threshold level is exceeded by said detected energy signal, that monotonically decreases in value as said prescribed threshold level is exceeded in greater amount by said detected energy signal, and that is zero for said detected energy signal reaching its own maximum value;

a first and a second multiplier each having a respective multiplicand input terminal, a respective multiplier input terminal and a respective product output terminal, the product output terminal of said first multiplier connecting to the multiplicand input terminal of said second multiplier, said high band video signal and said gain control signal and said folding carrier signal being applied to separate ones of the multiplicand input terminal of said first multiplier and the multiplier input terminal of said first multiplier and the multiplier input terminal of said second multiplier; and

means for linearly combining said video signal with a product signal supplied from the product output terminal of said second multiplier, to generate a combined signal.

7. Apparatus as set forth in claim 6, wherein said means for linearly combining said video signal with a product signal essentially consists of:

an adder connected for receiving said video signal as a first summand input signal, for receiving said product signal as a second summand input signal, and for supplying said combined signal as a sum output signal.

8. Apparatus as set forth in claim 6, further comprising:

means for lowpass filtering said combined signal, having a bandwidth that extends only to a frequency that is not higher than said carrier frequency.

9. Apparatus as set forth in claim 6, further comprising:

means for lowpass filtering said combined signal, having a bandwidth that extends only to a frequency that is not substantially higher than one half said carrier frequency.

10. Apparatus as set forth in claim 6, wherein said high band video signal is applied to the multiplicand input terminal of said first multiplier, said gain control signal is applied to the multiplier input terminal of said first multiplier, and said folding carrier signal is applied lo the multiplier input terminal of said second multiplier.

11. Apparatus as set forth in claim 6, wherein said high band video signal is applied to the multiplicand input terminal of said first multiplier, said folding carrier signal is applied to the multiplier input terminal of said first multiplier, and said gain control signal is applied to the multiplier input terminal of said second multiplier.

12. Apparatus as set forth in claim 6, wherein said means responsive to said detected energy signal exceeding a prescribed threshold level for generating a gain control signal comprises:

a rectifier for generating a rectified response to said detected energy signal exceeding said prescribed threshold level;

a lowpass filter for lowpass filtering said rectified response to said detected energy signal exceeding said prescribed threshold level to provide an average energy signal representing an average energy of said detected energy signal; and

a look-up table for providing said gain control signal in accordance with said average energy signal that is of maximum value until said prescribed threshold level is exceeded by said detected energy signal, that monotonically decreases in value as said prescribed threshold level is exceeded in greater amount by said detected energy signal, and that is zero when said detected energy signal reaches a maximum value.

13. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan line rate, said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier signal of a carrier frequency that is a multiple of said prescribed scan line rate and that is substantially the same in frequency as said upper video frequency;

means for reversing the phase of the carrier signal at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier signal;

a lowpass filter responsive to said video signal, for supplying a low band video signal extending up to a frequency at least as high as one half said carrier frequency;

a highpass filter responsive to said video signal, for supplying a high band video signal extending up from a frequency at least as low as one half said carrier frequency;

means for detecting the level of energy in said high band video signal, thereby to generate a detected energy signal;

means responsive to said detected energy signal exceeding a prescribed threshold levels for generating a gain control signal that is of maximum value until said prescribed threshold level is exceeded by said detected energy signal, that monotonically decreases in value as said prescribed threshold level is exceeded in greater amount by said detected energy signal, and that is zero for said detected energy signal reaching its own maximum value;

a first and a second multiplier each having a respective multiplicand input terminal, a respective multiplier input terminal and a respective product output terminal, the product output terminal of said first multiplier connecting to the multiplicand input terminal of said second multiplier, said high band video signal and said gain control signal and said folding carrier signal being applied to separate ones of the multiplicand input terminal of said first multiplier and the multiplier input terminal of said first multiplier and the multiplier input terminal of said second multiplier; and

means for linearly combining said low band video signal with a product signal supplied from the product output terminal of said second multiplier to generate a combined signal.

14. Apparatus as set forth in claim 13, wherein said means for linearly combining said video signal with a product signal essentially consists of:

an adder connected for receiving said video signal as a first summand input signal, for receiving said product signal as a second summand input signal, and for supplying said combined signal as a sum output signal.

15. Apparatus as set forth in claim 13 further comprising:

means for lowpass filtering said combined signal, having a bandwidth that extends only to a frequency that is not higher than said carrier frequency.

16. Apparatus as set forth in claim 13, further comprising:

means for lowpass filtering said combined signal, having a bandwidth extending across baseband past one half said upper video frequency, but not extending to said upper video frequency.

17. Apparatus as set forth in claim 13, wherein said high band video signal is applied to the multiplicand input terminal of said first multiplier, said gain control signal is applied to the multiplier input terminal of said first multiplier, and said folding carrier signal is applied to the multiplier input terminal of said second multiplier.

18. Apparatus as set forth in claim 13, wherein said high band video signal is applied to the multiplicand input terminal of said first multiplier, said folding carrier signal is applied to the multiplier input terminal of said first multiplier, and said gain control signal is applied to the multiplier input terminal of said second multiplier.

19. Apparatus as set forth in claim 13, wherein said means responsive to said detected energy signal exceeding a prescribed threshold level for generating a gain control signal comprises:

a rectifier for generating a rectified response to said detected energy signal exceeding said prescribed threshold level;

a lowpass filter for lowpass filtering said rectified response to said detected energy signal exceeding said prescribed threshold level to provide an average energy signal representing an average energy of said detected energy signal; and

a look-up table for providing said gain control signal in accordance with said average energy signal that is of maximum value until said prescribed threshold level is exceeded by said detected energy signal, that monotonically decreases in value as said prescribed threshold level is exceeded in greater amount by said detected energy signal, and that is zero when said detected energy signal reaches a maximum value.

20. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan lire rate, said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier of a carrier frequency that is a multiple of said prescribed scan line rate and that is at least as high in frequency as said upper video frequency;

means for reversing the phase of the carrier frequency at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier;

means for generating amplitude modulation of said folding carrier in accordance with said video signal; and

means for linearly combining said video signal and said amplitude modulation of said folding carrier to generate a combined signal.

21. Apparatus as set forth in claim 20, wherein said means for linearly combining said video signal and said amplitude modulation of said folding carrier consists of:

an adder connected for receiving said video signal as a first summand input signal, for receiving said amplitude modulation of said folding carrier as a second summand input signal, and for supplying said combined signal as a sum output signal.

22. Apparatus as set forth in claim 20, further comprising:

means for lowpass filtering said combined signal, having a bandwidth that extends only to a frequency that is not higher than said carrier frequency.

23. Apparatus as set forth in claim 20, further comprising:

means for lowpass filtering said combined signal, having a bandwidth extending across baseband past one half said upper video frequency, but not extending to said upper video frequency.

24. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line, at a prescribed scan lire rate, said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier of a carrier frequency that is a multiple of said prescribed scan line rate and that is at least as high in frequency as said upper video frequency;

means for reversing the phase of the carrier at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier;

de-emphasis means for de-emphasizing said upper video frequency of said video signal and providing said video signal having deemphasized high frequencies;

means for generating amplitude modulation of said folding carrier in accordance with said video signal having said deemphasized high frequencies; and

means for linearly combining said video signal and said amplitude modulation of said folding carrier to generate a combined signal having a first amplitude-modulation sideband that is lower in frequency than said carrier frequency and having a second amplitude-modulation sideband that is higher in frequency than said carrier frequency.

25. Apparatus as set forth in claim 24, wherein said de-emphasis means comprises:

a band-separation filter responding to said video signal for separating a lower video frequency portion and an upper video frequency portion from said video signal, said lower video frequency portion comprising only spectral components in a lower-frequency band extending up to said carrier frequency, and said upper video frequency portion comprising only spectral components in an upper-frequency band extending above said carrier frequency;

a rectifier for generating a rectified response to said upper video frequency portion separated from said video signal;

a threshold circuit for responding only to portions of said rectified response exceeding a predetermined threshold level;

a lowpass filter for producing in response to the response of said threshold circuit a deemphasis gain control signal dependent on the amount the level of said upper video frequency portion exceeds said predetermined threshold level;

means responsive to said deemphasis gain control signal, for generating a multiplier signal by multiplying said upper video frequency portion of said video signal by said deemphasis gain control signal; and

means for additively combining said multiplied signal with said lower video frequency portion of said video signal to provide said video signal having said de-emphasized high frequencies to said means for generating amplitude modulation of said folding carrier enabling generation of said combined signal.

26. Apparatus as set forth in claim 25, wherein said band-separation filter comprises:

a highpass filter for highpass filtering said video signal to separate said upper video frequency portion thereof; and

a lowpass filter for lowpass filtering said video signal to separate said lower video frequency portion thereof.

27. Apparatus as set forth in claim 25, wherein said means responsive to said deemphasis gain control signal for generating said multiplier signal essentially consists of means for subtracting said deemphasis gain control signal from a prescribed level.

28. Apparatus as set forth in claim 25, wherein said band-separation filter comprises:

a linear-phase finite-impulse-response filter comprising a tapped delay line with an odd number of taps spaced at one sample intervals, and a weighted summation circuit for weight samples with alternate negative and positive weights to provide a symmetrical kernel indicative of a highpass filter response of said video signal; and

a subtractor for subtracting from said video signal said upper video frequency portion separated from said video signal to provide said lower video frequency portion.

29. Apparatus as set forth in claim 25, wherein said de-emphasis means comprises:

means for separating an lower video frequency portion and an upper video frequency portion from said video signal;

means for rectifying said upper video frequency portion separated from said video signal to generate a rectified upper video frequency response;

means for baseline clipping said rectified upper video frequency response to generate a deemphasis gain control signal;

means for generating a multiplier signal having an amplitude that varies in response to said deemphasis gain control signal, growing smaller with increase in said deemphasis gain control signal and growing larger with decrease in said deemphasis gain control signal;

means for additively combining said multiplier signal with said lower video frequency portion separated from said video signal to provide said video signal having said de-emphasized high frequencies to said means for generating amplitude modulation of said folding carrier enabling generation of said combined signal.

30. Apparatus as set forth in claim 29, wherein said means for separating said lower video frequency portion and said upper video frequency portion from said video signal comprises:

a highpass filter for highpass filtering said video signal to generate said upper video frequency portion; and

a lowpass filter for lowpass filtering said video signal to generate said lower video frequency portion.

31. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan lire rate, said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier of a carrier frequency that is a multiple of said prescribed scan line rate and that is at least as high in frequency as said upper video frequency;

means for reversing the phase of the carrier at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier;

means for generating amplitude modulation of said folding carrier in accordance with said video signal, said amplitude modulation means comprising means for deemphasizing said upper video frequency of said video signal to generate a deemphasized high band video signal, and a

four-quadrant multiplier for multiplying said folding carrier with said deemphasized high band video signal to generate said amplitude modulation of said folding carrier; and

means for linearly combining said video signal and said amplitude modulation of said folding carrier to generate a combined signal.

32. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan lire rate. said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier of a carrier frequency that is a multiple of said prescribed scan line rate and that is at least as high in frequency as said upper video frequency;

means for reversing the phase of the carrier at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier;

means for generating amplitude modulation of said folding carrier in accordance with said video signal, said amplitude modulation means comprising;

means for detecting the energy level of upper video frequency of said video signal to generate a detected energy signal;

means responsive to said detected energy signal exceeding a prescribed threshold level, for generating a gain control signal that is of maximum value until said prescribed threshold level is exceeded by said detected energy signal, that monotonically decreases in value as said prescribed threshold level is exceeded in greater amount by said detected energy signal, and that is zero when said detected energy signal reaches its own maximum value;

a first four-quadrant multiplier for multiplying said gain control signal with said upper video frequency of said video signal to generate a deemphasized high band video signal; and

a second four-quadrant multiplier for multiplying said folding carrier with said deemphasized high band video signal to generate said amplitude modulation of said folding carrier; and

means for linearly combining said video signal and said amplitude modulation of said folding carrier to generate a combined signal.

33. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan line rate, said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier frequency that is a multiple of said prescribed scan line rate and that is at least as high in frequency as said upper video frequency;

means for reversing the phase of the carrier frequency at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier;

a highpass filter responsive to said video signal, for supplying a high band video signal;

means for detecting the level of energy in said high band video signal, thereby to generate a detected energy signal;

means responsive to said detected energy signal exceeding a prescribed threshold level for generating a gain control signal that is of maximum value until said prescribed threshold level is exceeded by said detected energy signal, that monotonically decreases in value as said prescribed threshold level is exceeded in greater amount by said detected energy signal, and that is zero for said detected energy signal reaching its own maximum value;

means for generating amplitude modulation of said folding carrier in accordance with said video signal;

means for regulating said amplitude modulation of said folding carrier in accordance with said gain control signal, included in said means for generating amplitude modulation of said folding carrier in accordance with said video signal; and

means for linearly combining said video signal and said amplitude modulation of said folding carrier to generate a combined signal.

34. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan line rate, said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier frequency that is a multiple of said prescribed scan line rate and that is at least as high in frequency as said upper video frequency;

means for reversing the phase of the carrier frequency at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier;

a lowpass filter responsive to said video signal, for supplying a low band video signal extending up to a frequency at least as high as one half said carrier frequency;

a highpass filter responsive to said video signal, for supplying a high band video signal extending up from a frequency at least as low as one half said carrier frequency;

means for generating amplitude modulation of said folding carrier in accordance with said high band video signal; and

means for combining said low band video signal with at least the portion of said amplitude modulation of said folding carrier extending up to a frequency at least as high as one half said carrier frequency, thereby providing a folded-spectrum video signal.

35. Apparatus as set forth in claim 34, wherein said means for generating amplitude modulation of said folding carrier in accordance with said high band video signal comprises:

means for deemphasizing said high band video signal to generate a deemphasized high band video signal; and

a four-quadrant multiplier for multiplying said folding carrier with said deemphasized high band video signal to generate said amplitude modulation of said folding carrier.

36. Apparatus as set forth in claim 34, wherein said means for generating amplitude modulation of said folding carrier in accordance with said high band video signal comprises:

means for detecting the level of energy in said high band video signal to generate a detected energy signal;

means responsive to said detected energy signal exceeding a prescribed threshold level for generating a gain control signal that is of maximum value until said prescribed threshold level is exceeded by said detected energy signal, that monotonically decreases in value as said prescribed threshold level is exceeded in greater amount by said detected energy signal, and that is zero for said detected energy signal reaching its own maximum value;

a first four-quadrant multiplier for multiplying said gain control signal with said high band video signal to generate a deemphasized high band video signal; and

a second four-quadrant multiplier for multiplying said folding carrier with said deemphasized high band video signal to generate said amplitude modulation of said folding carrier.

37. Apparatus for folding the spectrum of a full-band video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan line rate, said apparatus comprising:

a source of said full-band video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier frequency that is a multiple of said prescribed scan line rate and that is at least as high in frequency as said upper video frequency;

means for reversing the phase of the carrier frequency at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier;

a band-splitting filter responsive to said full-band video signals for supplying a low band video signal and a high band video signal respectively substantially below and substantially above a crossover frequency that is one half said carrier frequency;

means for adaptively deemphasizing said high band video signal to generate a deemphasized high band video signal;

means for combining said deemphasized high band video signal and said low band video signal to generate a modified full-band video signal;

means for generating amplitude modulation of said folding carrier in accordance with said modified full-band video signal;

means for combining said modified full-band video signal with said amplitude modulation of said folding carrier to generate a combined signal; and

a lowpass filter for receiving said combined signal and for supplying response to the portion of said combined signal that is below said crossover frequency, and suppressing the portion of said combined signal that is above said crossover frequency.

38. Apparatus as set forth in claim 37, wherein said means for adaptively deemphasizing said high band video signal to generate said deemphasized high band video signal comprises:

a rectifier for generating a rectified response to said high band video signal;

a threshold circuit for responding only to portions of said rectified response exceeding a predetermined threshold level;

a lowpass filter for generating said deemphasis gain control signal by lowpass filtering said high band video signal, said deemphasis gain control signal being varied in response to the energy level of said high band video signal exceeding said predetermined threshold level;

means responsive to said deemphasis gain control signal, for generating a multiplier signal by multiplying said high band video signal by said deemphasis gain control signal; and

means for additively combining said multiplied signal with said low band video signal to provide said modified full-band video signal.

39. Apparatus as set forth in claim 38, wherein said band-splitting filter comprises:

a highpass filter for highpass filtering said full-band video signal to generate said high band video signal above said crossover frequency that is one half said carrier frequency; and

a lowpass filter for lowpass filtering said full-band video signal to generate said low band video signal below said crossover frequency that is one half said carrier frequency.

40. Apparatus for folding the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan line rate, said apparatus comprising:

a source of said video signal having a bandwidth extending across baseband to an upper video frequency;

a generator of a carrier frequency that is a multiple of said prescribed scan line rate and that is at least as high in frequency as said upper video frequency;

means for reversing the phase of the carrier frequency at said prescribed scan line rate, each reversal being at a respective instant between successive scan lines, to supply a folding carrier;

a lowpass filter responsive to said video signal for supplying a low band video signal extending up to a frequency at least as high as one half said carrier frequency;

a highpass filter responsive to said video signal for supplying a high band video signal extending up from a frequency at least as low as one half said carrier frequency;

means for adaptively deemphasizing said high band video signal to generate a deemphasized high band video signal;

means for generating amplitude modulation of said folding carrier in accordance with said deemphasized high band video signal;

means for combining said low band video signal with at least the portion of said amplitude modulation of said folding carrier extending up to a frequency at least as high as one half said carrier frequency, thereby providing a folded-spectrum video signal.

41. Apparatus as set forth in claim 40, wherein said means for adaptively deemphasizing said high band video signal to generate said deemphasized high band video signal comprises:

a rectifier for generating a rectified response to said high band video signal;

a threshold circuit for responding only to portions of said rectified response exceeding a predetermined threshold level;

a lowpass filter for generating said deemphasis gain control signal by lowpass filtering said high band video signal, said deemphasis gain control signal being varied in response to the energy level of said high band video signal exceeding said predetermined threshold level;

means responsive to said deemphasis gain control signal, for generating a multiplier signal by multiplying said high band video signal by said deemphasis gain control signal; and

means for additively combining said multiplied signal with said low band video signal to provide said modified full-band video signal.

42. Apparatus for reversing the spectrum of a video signal descriptive of the scanning of successive image frames supplied at a prescribed frame rate, which scanning is done line-by-line at a prescribed scan line rate, said apparatus comprising:

a source of said video signal having a lower video frequency portion and an upper video frequency portion;

a generator of a carrier signal of a carrier frequency that is a multiple of said prescribed scan line rate and above said upper video frequency portion;

a multiplier having a multiplicand input terminal coupled to receive one of said video signal and said carrier signal and a multiplier input terminal coupled to receive another of said video signal and said carrier signal, for generating a product signal having a first amplitude-modulation sideband that is lower in frequency than said carrier frequency and having a second amplitude-modulation sideband that is higher in frequency than said carrier frequency;

de-emphasis means for de-emphasizing said upper video frequency portion of said video signal and providing said video signal with deemphasized high frequencies to said multiplier for enabling generation of said product signal; and

means for reversing at said prescribed scan line rate the phase of the carrier signal received by said multiplier, each reversal being at a respective instant between successive scan lines, thereby enabling conversion of said product signal into a reversed-spectrum video signal with line-to-line inversion of phase.

43. Apparatus as set forth in claim 42, wherein said de-emphasis means comprises:

a band-separation filter responding to said video signal for separating said lower video frequency portion and said upper video frequency portion from said video signal, said lower video frequency portion comprising only spectral components in a lower-frequency band extending up to said carrier frequency, and said upper video frequency portion comprising only spectral components in an upper-frequency band extending above said carrier frequency;

a rectifier for generating a rectified response to said upper video frequency portion separated from said video signal;

a threshold circuit for responding only to portions of said rectified response exceeding a predetermined threshold level;

a lowpass filter for producing in response to the response of said threshold circuit a deemphasis gain control signal dependent on the amount the level of said upper video frequency portion exceeds said predetermined threshold level;

means responsive to said deemphasis gain control signal, for generating a multiplier signal by multiplying said upper video frequency portion of said video signal by said gain control signal; and

means for additively combining said multiplied signal with said lower video frequency portion of said video signal to provide said video signal having said de-emphasized high frequencies to said multiplier for enabling generation of said product signal having said first amplitude-modulation sideband that is lower in frequency than said carrier frequency and having said second amplitude-modulation sideband that is higher in frequency than said carrier frequency.

44. Apparatus as set forth in claim 43, wherein said band-separation filter comprises:

a highpass filter for highpass filtering said video signal to separate said upper video frequency portion thereof; and

a lowpass filter for lowpass filtering said video signal to separate said lower video frequency portion thereof.

45. Apparatus as set forth in claim 43, wherein said means responsive to said deemphasis gain control signal for generating said multiplier signal essentially consists of means for subtracting said deemphasis gain control signal from a prescribed level.

46. Apparatus as set forth in claim 44, wherein said band-separation filter is a tapped-delay-line filter comprising:

a tapped delay line coupled to receive said video signal, having an odd number of taps for supplying consecutively numbered tap signals with increasing increments of delay;

a first weighted summation circuit for generating a first weighted sum of odd-numbered ones of said consecutively numbered tap signals, as weighted by weights of a first polarity;

a second weighted summation circuit for generating a second weighted sum of even-numbered ones of said consecutively numbered tap signals, as weighted by weights of first polarity;

an adder for additively combining said first and second weighted sums to provide said lower frequency portion of said video signal; and

a subtractor for differentially combining said first and second weighted sums to provide said upper frequency portion of said video signal.

47. Apparatus as set forth in claim 44, wherein said band-separation filter is a tapped-delay-line filter comprising:

a tapped delay line coupled to receive said video signal, having an odd number of taps for supplying consecutively numbered tap signals with increasing increments of delay;

a first weighted summation circuit for generating a first weighted sum of odd-numbered ones of said consecutively numbered tap signals, as weighted by weights of a first polarity;

a second weighted summation circuit for generating a second weighted sum of even-numbered ones of said consecutively numbered tap signals, as weighted by weights of said first polarity;

a third weighted summation circuit for generating a third weighted sum of even-numbered ones of said consecutively numbered tap signals, as weighted by weights of a second polarity opposite to said first polarity;

a first adder combining said first and second weighted sums to provide said lower frequency portion of said video signal; and

a second adder combining said first and third weighted sums to provide said upper frequency portion of said video signal.

48. Apparatus as set forth in claim 43, wherein said band-separation filter comprises:

a linear-phase finite-impulse-response filter comprising a tapped delay line with an odd number of taps spaced at one sample intervals, and a weighted summation circuit for weight samples with alternate negative and positive weights to provide a symmetrical kernel indicative of a highpass filter response of said video signal; and

a subtractor for subtracting from said video signal said upper video frequency portion separated from said video signal to provide said lower video frequency portion.

49. Apparatus as set forth in claim 42, wherein said de-emphasis means comprises:

means for separating said lower video frequency portion and said upper video frequency portion from said video signal;

means for rectifying said upper video frequency portion separated from said video signal to generate a rectified upper video frequency response;

means for baseline clipping said rectified upper video frequency response to generate a deemphasis gain control signal;

means for generating a multiplier signal having an amplitude that varies in response to said deemphasis gain control signal, growing smaller with increase in said deemphasis gain control signal and growing larger with decrease in said deemphasis gain control signal;

means for additively combining said multiplier signal with said lower video frequency portion separated from said video signal to provide said video signal having said de-emphasized high frequencies to said multiplier for enabling generation of said product signal having said first amplitude-modulation sideband that is lower in frequency than said carrier frequency and having said second amplitude-modulation sideband that is higher in frequency than said carrier frequency.

50. Apparatus as set forth in claim 49, wherein said means for separating said lower video frequency portion and said upper video frequency portion from said video signal comprises:

a highpass filter for highpass filtering said video signal to generate said upper video frequency portion; and

a lowpass filter for lowpass filtering said video signal to generate said lower video frequency portion.

51. Apparatus as set forth in claim 44, wherein said band-separation filter is a tapped-delay-line filter comprising:

a tapped delay line coupled to receive said video signal, having an odd number of taps for supplying consecutively numbered tap signals with increasing increments of delay;

a first weighted summation circuit for generating a first weighted sum of odd-numbered ones of said consecutively numbered tap signals, as weighted by weights of a first polarity;

a second weighted summation circuit for generating a second weighted sum of even-numbered ones of said consecutively numbered tap signals, as weighted by weights of first polarity;

an adder for additively combining said first and second weighted sums to provide said lower frequency portion of said video signal; and

a subtractor for differentially combining said first and second weighted sums to provide said upper frequency portion of said video signal.

52. Apparatus as set forth in claim 44, wherein said band-separation filter is a tapped-delay-line filter comprising:

a tapped delay line coupled to receive said video signal, having an odd number of taps for supplying consecutively numbered tap signals with increasing increments of delay;

a first weighted summation circuit for generating a first weighted sum of odd-numbered ones of said consecutively numbered tap signals, as weighted by weights of a first polarity;

a second weighted summation circuit for generating a second weighted sum of even-numbered ones of said consecutively numbered tap signals, as weighted by weights of said first polarity;

a third weighted summation circuit for generating a third weighted sum of even-numbered ones of said consecutively numbered tap signals, as weighted by weights of a second polarity opposite to said first polarity;

a first adder combining said first and second weighted sums to provide said lower frequency portion of said video signal; and

a second adder combining said first and third weighted sums to provide said upper frequency portion of said video signal.