Image processing apparatus with variable clamping

• US 5,448,306 A
• Filed: 06/18/1993
• Issued: 09/05/1995
• Est. Priority Date: 06/30/1992
• Status: Expired due to Term

• Current Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Original Assignee: Canon Ayutthaya Limited (Canon Inc.)
• Inventors: Koyama, Shinichi
• Primary Examiner(s): Groody, James J.
• Assistant Examiner(s): Grant, Chris
• Application Number:
  US08/078,115
• Time in Patent Office: 809 Days
• Field of Search: 358/174, 358/172, 358/171, 358/34, 358/37
• US Class Current: 348/678
• CPC Class Codes: H04N 5/18 by means of "clamp" circuit operated by switching circuit
• CPC Class Codes: H04N 5/52 Automatic gain control

Abstract

Image processing apparatus wherein the level of an input analog picture signal from an imaging device is controlled by gain control circuitry, and the gain-controlled analog signal is then converted into a digital signal. Feedback clamping is performed by generating an error signal by subtracting a target value from the digital signal, and then adding the error signal to the gain-controlled analog signal. Correct clamping is made possible by allowing the target value to be varied based upon the gain set by the gain control means.

Claims

1. Image processing apparatus for processing an input analog image signal, comprising:

a) gain control means for controlling a level of the input analog image signal;

b) A/D conversion means for converting the analog image signal output from said gain control means into a digital image signal; and

c) modifying means for modifying a level of said digital image signal by using a reference signal, said modifying means including subtracting means for obtaining a difference between the digital image signal and the reference signal, said modifying means varying a level of the reference signal and a level of said gain control means, said modifying means varying the level of the reference signal in accordance with the level of said gain control means, said modifying means being capable of modifying said digital image signal level irrespective of the digital image signal.

2. An imaging apparatus, comprising:

a) imaging means for converting object light into an analog image signal;

b) gain control means, coupled to said imaging means, for controlling the level of the analog image signal output from said imaging means;

c) A/D conversion means, coupled to said gain control means, for converting the analog image signal output from said gain control means into a digital image signal;

d) processing means, coupled to said gain control means, for obtaining a difference between adding a reference signal and said digital image signal output from said A/D conversion means; and

e) control means, coupled to said processing means and to said gain control means, for controlling the level of said reference signal in accordance with the gain of said gain control means, and for controlling the gain of said gain control means.

3. An imaging apparatus according to claim 2, wherein said control means raises the gain of said gain control means when the level of said analog image signal output from said gain control means is low, and lowers the gain of said gain control means when the level of said analog image signal output from said gain control means is high.

4. An imaging apparatus according to claim 2, wherein said control means lowers the level of the reference signal when the level of said analog signal output from said gain control means is low, and raises the level of the reference signal when the level of said analog signal output from said gain control means is high.

5. An imaging apparatus according to claim 2, further comprising signal generating means for generating an error signal based upon a signal output from said processing means, said signal generating means including averaging means for averaging the signals output from said processing means for a predetermined period of time.

6. An imaging apparatus according to claim 5, wherein said signal generating means further comprises an integrating circuit which integrates a signal output from said averaging means.

7. An imaging apparatus according to claim 5, further comprising second processing means for adding said error signal and said analog signal output from said gain control means, and wherein said A/D conversion means converts the analog signal output from said second processing means into a digital signal.

8. An imaging apparatus according to claim 2, wherein the level of the reference signal is close to the lower limit level of said A/D conversion means.

9. An imaging apparatus according to claim 2, further comprising signal processing means for performing a predetermined signal processing on the signal output from said processing means.

10. An imaging apparatus according to claim 9, further comprising a recording means for recording the signal output from said signal processing means on a recording medium, and wherein said recording means includes a rotating head.

11. Image processing apparatus for processing an input analog image signal, comprising:

a) gain control means for controlling the level of the input analog image signal;

b) A/D conversion means for converting the analog image signal output from said gain control means into a digital image signal;

c) processing means for processing the digital image signal and a reference signal; and

d) adding means for adding an error signal which corresponds to the signal output from said processing means to said analog image signal output from said gain control means, said processing means varying the level of the reference signal in accordance with the gain of said gain control means.

12. An apparatus according to claim 11, wherein said processing means includes a subtracting circuit for subtracting the reference signal from the digital image signal, and wherein said error signal corresponds to a signal output from said subtracting circuit.

13. An apparatus according to claim 12, further comprising D/A conversion means for converting the error signal into an analog error signal.

14. An apparatus according to claim 11, further comprising imaging means for converting object light into the input analog image signal.

15. An apparatus according to claim 14, further comprising:

signal processing means for performing a predetermined signal processing on the digital image signal output from said processing means.

16. An apparatus according to claim 15, further comprising:

recording means for recording the digital image signal output from said signal processing means on a recording medium.

17. An apparatus according to claim 16, wherein said recording medium comprises a magnetic tape.

18. A signal processing apparatus, comprising:

a) gain control means for controlling a level of a received analog image signal, and for converting the received analog image signal into a digital image signal; and

b) modifying means for modifying a level of the digital image signal by using a reference signal, said modifying means including subtracting means for obtaining a difference between the digital image signal and the reference signal, said modifying means varying a level of the reference signal according to the level set by said gain control means, said modifying means being capable of modifying the level of the digital image signal irrespective of the digital image signal.

19. An apparatus according to claim 18, wherein said subtracting means includes a subtracting circuit for subtracting the reference signal from the digital image signal.

20. An apparatus according to claim 18, further comprising:

imaging means for converting object light into the received analog image signal.

21. An apparatus according to claim 20, further comprising:

signal processing means for performing a predetermined signal processing on the digital image signal output from said modifying means.

22. An apparatus according to claim 21, further comprising:

recording means for recording the digital image signal output from said signal processing means on a recording medium.

23. An apparatus according to claim 22, wherein said recording medium comprises a magnetic tape.

24. A signal processing apparatus, comprising:

a) gain control means for controlling a level of a received analog image signal, and for converting the received analog image signal into a digital image signal; and

b) modifying means for modifying a level of the digital image signal by using a reference signal, said modifying means including subtracting means for obtaining a difference between the digital image signal and the reference signal, said modifying means varying a level of the reference signal and a level of said gain control means,, said modifying means being capable of modifying the level of the digital image signal irrespective of the digital image signal.

25. An apparatus according to claim 24, wherein said subtracting means includes a subtracting circuit for subtracting the reference signal from the digital image signal.

26. An apparatus according to claim 24, further comprising:

imaging means for converting object light into the received analog image signal.

27. An apparatus according to claim 26, further comprising:

signal processing means for performing a predetermined signal processing on the digital image signal output from said modifying means.

28. An apparatus according to claim 27, further comprising:

recording means for recording the digital image signal output from said signal processing means on a recording medium.

29. An apparatus according to claim 28, wherein said recording medium comprises a magnetic tape.

30. A signal processing apparatus, comprising:

(a) gain control means for controlling a level of a received analog image signal, and for converting the received analog image signal into a digital image signal; and

(b) modifying means for modifying a level of the digital image signal by using a reference signal, said modifying means including subtracting means for obtaining a difference between the digital image signal and the reference signal, said modifying means varying a level of the reference signal and a level of said gain control means, said modifying means includes a control means for controlling the level of the reference signal according to the level of said gain control means, said modifying means being capable of modifying the level of the digital image signal irrespective of the digital image signal.

31. A signal processing apparatus, comprising:

a) first level adjusting means for controlling a level of a received analog image signal, and for converting the analog image signal into a digital image signal;

b) second level adjusting means for adjusting a level of the digital image signal, said second level adjusting means including subtracting means for obtaining a difference between the digital image signal and a reference signal; and

c) control means for controlling said first and second level adjusting means, said control means being capable of controlling an operation of said second level adjusting means irrespective of the digital image signal.

32. An apparatus according to claim 31, wherein said subtracting means includes a subtracting circuit for subtracting a reference signal from the digital image signal.

33. An apparatus according to claim 32, wherein said control means controls a level of said first level adjusting means and a level of the reference signal.

34. An apparatus according to claim 33, wherein said control means controls the level of the reference signal according to the level of said first level adjusting means.

35. An apparatus according to claim 31, wherein said first level adjusting means includes (i) a gain control circuit for controlling the level of the received analog image signal, and (ii) an A/D converter for converting the analog image signal into a digital image signal, said gain control means controlling the level of the received analog image signal in accordance with the level of the analog image signal output from said first level adjusting means.

36. An apparatus according to claim 31, further comprising:

imaging means for converting object light into the received analog image signal.

37. An apparatus according to claim 36, further comprising:

signal processing means for performing a predetermined signal processing on the digital image signal output from said second level adjusting means.

38. An apparatus according to claim 37, further comprising:

recording means for recording the digital image signal output from said signal processing means on a recording medium.

39. An apparatus according to claim 38, wherein said recording medium comprises a magnetic tape.

40. An apparatus according to claim 31 incorporated into a digital VCR.