ANALOG VIDEO CHROMAKEY MIXER

• US 20020075411A1
• Filed: 01/05/1998
• Published: 06/20/2002
• Est. Priority Date: 06/28/1994
• Status: Active Grant

• Current Assignee: V-Silicon Semiconductors (HEFEI) Co., Ltd.
• Original Assignee: Sigma Designs Incorporated
• Inventors: NGUYEN, JULIEN T.
• Granted Patent: US 6,421,096 B1
• Time in Patent Office: Days
• US Class Current: 348/587
• CPC Class Codes: H04N 9/75 Chroma key

Abstract

An improved technique for mixing picture signals directed at a monitor screen. Two analog video signals (such as an analog VGA input and an analog ROB signal produced in response to a stored digital still or moving image) may be multiplexed in analog form. An analog chromakey mixer detects a background color in the first video signal (such as the analog VGA input), and replaces the portion of that first video signal with the second video signal. The time delays of the first video signal and the second video signal may be adjusted so that they reach the monitor screen (by means of a multiplexer output) at the same time. An alignment detector may attempt to align two known signals (such as a VGA sync signal and a signal generated for this purpose), and may adjust a set of time delays in the analog chromakey mixer until the time difference between the first and second video signals falls below a threshold.

Claims

3. A device, comprising

means for receiving a first analog video signal;

means for receiving a second analog video signal;

means for detecting a chromakey in said first analog video signal and for generating a comparison signal in response thereto;

means for replacing a portion of said first analog video signal with a portion of said second analog video signal in response to said comparison signal;

means for measuring a difference between a first time delay and a second time delay, said first time delay comprising a delay from input to output of said first analog video signal, said second time delay comprising a delay from input to output of said second analog video signal; and

means for adjusting said at least one time delay, so that said first time delay and said second time delay are substantially equal.

4. A device as in claim 3, wherein said means for adjusting comprises

means for supplying a selected first video input to said means for receiving said first analog video signal;

means for supplying a selected second video input to said means for receiving said second analog video signal;

means for comparing an output of said means for replacing with a selected analog video signal; and

means for controlling at least one time delay circuit in response to said means for comparing.

5. A device as in claim 3, wherein said means for adjusting comprises

means for supplying a selected first video input to said means for receiving said first analog video signal;

means for supplying a selected second video input to said means for receiving said second analog video signal;

means for comparing an output of said means for replacing with a selected analog video signal; and

means for controlling at least one time delay circuit to minimize a difference between said output of said means for replacing and said selected analog video signal.

6. A device as in claim 3, wherein said means for adjusting comprises

means for supplying a selected first video input to said means for receiving said first analog video signal;

means for supplying a selected second video input to said means for receiving said second analog video signal;

means for comparing an output of said means for replacing with a selected analog video signal;

means for tentatively selecting a first and a second one of a plurality of possible time delays for said time delay circuit;

means for examining an output of said means for comparing for said first and said second one possible time delays, responsive to said means for tentatively selecting; and

means for permanently selecting said first or said second one possible time delay in response to said means for examining.

7. A device as in claim 6, wherein said means for tentatively selecting repeatedly selects possible combinations of time delays for a plurality of time delay circuits until a difference between said output of said means for replacing and said selected analog video signal falls below a selected threshold.

8. A device as in claim 6, wherein said means for tentatively selecting selects substantially all possible combinations of time delays for a plurality of time delay circuits, and wherein said means for permanently selecting selects one of said substantially all possible combinations that minimizes a difference between said output of said means for replacing and said selected analog video signal.

9. A device as in claim 3, wherein said first analog video signal is an analog VGA input.

10. A device as in claim 3, wherein said means for replacing comprises an analog multiplexer coupled to said first analog video signal, said second analog video signal, and said comparison signal.

11. A device as in claim 3, wherein said second analog video signal is an analog RGB signal produced in response to a stored digital still or moving image.

15. A video system as in claim 14, comprising a video monitor coupled to an output of said analog chromakey mixer.

16. A video system as in claim 14, wherein said means for receiving analog video is coupled to a monitor driver circuit.

20. A method as in claim 19, wherein said step of adjusting comprises the steps of

supplying a selected first video input;

supplying a selected second video input;

comparing a result of said step of replacing with a selected analog video signal; and

controlling at least one time delay circuit in response to said step of comparing.

21. A method as in claim 19, wherein said step of adjusting comprises the steps of

supplying a selected first video input;

supplying a selected second video input;

comparing a result of said step of replacing with a selected analog video signal; and

controlling at least one time delay circuit to minimize a difference between said result of said step of replacing and said selected analog video signal.

22. A method as in claim 19, wherein said step of adjusting comprises the steps of

supplying a selected first video input;

supplying a selected second video input;

comparing a result of said step of replacing with a selected analog video signal;

tentatively selecting a first and a second one of a plurality of possible time delays for said time delay;

examining a result of said step of comparing for said first and said second one possible time delays; and

permanently selecting said first or said second one possible time delay in response to said step of examining.

23. A method as in claim 22, wherein said step of tentatively selecting selects substantially all possible combinations of time delays for a plurality of time delay circuits, and wherein said step of permanently selecting selects one of said substantially all possible combinations that minimizes a difference between said result of said step of replacing and said selected analog video signal.

24. A method as in claim 22, wherein said step of tentatively selecting is performed repeatedly to select possible combinations of time delays for a plurality of time delay circuits until a difference between said result of said step of replacing and said selected analog video signal falls below a selected threshold.

25. A method as in claim 24, wherein said step of receiving a second analog video signal comprises the steps of producing an analog RGB signal in response to a stored digital still or moving image, and receiving said analog RGB signal.

26. A method as in claim 24, wherein said step of replacing comprises the step of using an analog multiplexer coupled to said first analog video signal, said second analog video signal, and said comparison signal.

28. A video system as in claim 27, comprising the step of displaying a result of said step of multiplexing.

30. A method as in claim 29, comprising the step of displaying a result of said step of replacing.

31. A device as in claim 4, wherein said selected analog video signal comprises an all-black signal.

32. A method as in claim 20, wherein said selected analog video signal comprises an all-black signal.

12. A video system, comprising

a digital signal processor coupled to a source of digital video;

a video D/A converter coupled to an output of said digital signal processor;

an analog video input;

a chromakey detector coupled to said analog video input;

an analog multiplexer coupled to an output of said video D/A converter, to said analog video input, and to said chromakey detector;

at least one adjustable delay coupled to an input of said analog multiplexer; and

an alignment detector coupled to an output of said analog multiplexer.

13. A video system, comprising

a sync input;

a phase locked loop coupled to said sync input;

a first delay circuit coupled to said phase locked loop;

a digital signal processor coupled to said sync input and to said first time delay circuit;

a video D/A converter coupled to an output of said digital signal processor;

a second and a third delay circuit coupled to said digital signal processor;

an analog video input;

a chromakey detector coupled to said analog video input;

a logic circuit coupled to said chromakey detector and to said second and third delay circuits;

a fourth delay circuit coupled to said analog video input;

an analog multiplexer coupled to an output of said D/A converter, to an output of said fourth delay circuit, and to said logic circuit; and

an alignment detector coupled to an output of said analog multiplexer.

14. A video system, comprising

means for receiving analog video;

a digital signal processor coupled to a source of digital video;

a D/A converter coupled to said digital signal processor;

an analog chromakey mixer coupled to an output of said D/A converter and to said means for receiving analog video;

at least one adjustable delay coupled to an input of said analog chromakey mixer; and

an alignment detector coupled to an output of said analog multiplexer.

19. A method comprising the steps of

receiving a first analog video signal;

receiving a second analog video signal;

detecting a chromakey in said first analog video signal and generating a comparison signal in response thereto;

replacing a portion of said first analog video signal with a portion of said second analog video signal in response to said comparison signal;

adjusting at least one time delay between said means for receiving a first analog video signal and said means for replacing;

measuring a difference between a first time delay and a second time delay, said first time delay comprising a delay from input to output of said first analog video signal, said second time delay comprising a delay from input to output of said second analog video signal; and

adjusting at least one time delay, so that said first time delay and said second time delay are substantially equal.

27. A method comprising the steps of

receiving a first analog video signal;

converting a source of digital video to a second analog video signal;

multiplexing said first analog video signal and said second analog video signal;

measuring a difference between a first time delay ad a second time delay, said first time delay comprising a delay from input to output of said first analog video signal, said second time delay comprising a delay from input to output of said second analog video signal; and

adjusting at least one time delay, responsive to said step of measuring, so that said first time delay and said second time delay are substantially equal.

29. A method comprising the steps of

receiving a first analog video signal;

detecting a chromakey in said first analog video signal;

converting a source of digital video to a second analog video signal;

replacing a portion of said first analog video signal with a portion of said second analog video signal in response to said chromakey;

measuring a difference between a first time delay ad a second time delay, said first time delay comprising a delay from input to output of said first analog video signal, said second time delay comprising a delay from input to output of said second analog video signal; and

adjusting at least one time delay, responsive to said step of measuring, so that said first time delay and said second time delay are substantially equal.

33. Apparatus including

a first input port disposed for receiving a first analog video signal;

a second input port disposed for receiving a second analog video signal;

a chromakey detector coupled to said first input port;

a multiplexer coupled to said chromakey detector, said first input port, and said second input port;

an output port coupled to said multiplexer;

an adjusting circuit disposed for adjusting a time delay in said apparatus, whereby a difference is minimized between a first time delay between said first input port and said output port and a second time delay between said second input port and said output port.

34. Apparatus as in claim 33, including

a clock input port disposed for receiving a clock signal;

and

a detector coupled to said output port, said detector being responsive to an output signal appearing at said output port, said output signal including a plurality of horizontal lines each having a plurality of pixels, said pixels being responsive to said clock signal.

35. Apparatus as in claim 33, including a control input port disposed for receiving a signal indicative of a status of said second analog video signal.

36. Apparatus as in claim 35, including a circuit coupled to said control input port, to said chromakey detector, and to said multiplexer.

37. Apparatus as in claim 33, including a detector coupled to said output port, said detector being responsive to an output signal appearing at said output port, said output signal including a plurality of horizontal lines each having a plurality of pixels.

38. Apparatus as in claim 33, wherein said time delay includes a time delay between said chromakey detector and said multiplexer.

39. Apparatus as in claim 33, wherein said time delay includes a time delay between said first input port and said chromakey detector.

40. Apparatus as in claim 33, wherein said time delay includes a time delay between said first input port and said multiplexer.

41. Apparatus as in claim 33, wherein said time delay includes a time delay between said second input port and said chromakey detector.

42. Apparatus as in claim 33, wherein said time delay includes a time delay between said second input port and said multiplexer.

43. Apparatus as in claim 33, wherein said time delay includes a coarse time delay and a fine time delay.

44. A method including the steps of

receiving a first analog video signal;

receiving a second analog video signal;

detecting a chromakey in said first analog video signal;

replacing at least a portion of said analog video signal with at least a portion of said second analog video signal in response to said chromakey;

outputting a resultant signal of said step of replacing;

adjusting a time delay, whereby a difference is minimized between a first time delay between said step of receiving said first analog video signal and said step of outputting and a second time delay between said step of receiving said second analog video signal and said step of outputting.

45. A method as in claim 44, including the steps of

receiving a clock signal;

and

detecting said resultant signal, said resultant signal including a plurality of horizontal lines each having a plurality of pixels, said pixels being responsive to said clock signal.

46. A method as in claim 44, including the step of receiving a control signal, said control signal being indicative of a status of said second analog video signal.

47. A method as in claim 46, wherein said step of replacing is responsive to said control signal.

48. A method as in claim 44, including the step of detecting said resultant signal, wherein said resultant signal includes a plurality of horizontal lines each having a plurality of pixels.

49. A method as in claim 44, wherein said time delay includes a time delay between said step of detecting a chromakey and said step of replacing.

50. A method as in claim 44, wherein said time delay includes a time delay between said step of receiving a first analog video signal and said step of detecting a chromakey.

51. A method as in claim 44, wherein said time delay includes a time delay between said step of receiving a first analog video signal said step of replacing.

52. A method as in claim 44, wherein said time delay includes a time delay between said step of receiving a second analog video signal and said step of detecting a chromakey.

53. A method as in claim 44, wherein said time delay includes a time delay between said step of receiving a second analog video signal and said step of replacing.

54. A method as in claim 44, wherein said time delay includes a coarse time delay and a fine time delay.