Parabolic mixer for video signals

• US 6,469,747 B1
• Filed: 09/02/1999
• Issued: 10/22/2002
• Est. Priority Date: 09/02/1999
• Status: Expired due to Term

• Current Assignee: Blackmagic Design Pty Limited
• Original Assignee: Da Vinci Intellectual Property (Blackmagic Design Pty Limited)
• Inventors: Gibson, Joel D., Rai, Sanjay Devappa
• Primary Examiner(s): HSIA, SHERRIE Y
• Application Number:
  US09/389,150
• Time in Patent Office: 1,146 Days
• Field of Search: H04/N.974, H04/N.976, H04/N.964, H04/N.968, H04/N.557, 348/584, 348/585, 348/598, 348/599, 348/650, 348/645, 348/649, 348/588, 348/687
• US Class Current: 348/584
• CPC Class Codes: H04N 5/265 Mixing
• CPC Class Codes: H04N 9/76 for mixing of colour signals H04N9/75 takes precedence

Abstract

A video signal mixer with a parabolic signal mixing function, especially useful in scene-by-scene color correction systems and “blue screen” video masking applications. The mixer effects mixing two independent signal sources while smoothly controlling the rate of change during mixing. An input stage receives a first video signal and a second video signal. The mixing circuit mixes the first video signal with the second video signal based on a predetermined parabolic function. An aperture signal circuit in the mixer allows a degree of operator control over the parabolic function. An output stage provides a parabolized output signal. The output signal, which comprises the mixture of the first video signal and the second video signal, eliminates discontinuities in regions of the signal which would otherwise produce discontinuities in prior art types of video signal mixers.

Claims

1. A signal mixer for mixing a first video signal with a second video signal while smoothly controlling the rate of change for an output signal, comprising:

an input stage for receiving the first video signal and the second video signal;

a mixing circuit for mixing the first video signal with the second video signal based on a predetermined parabolic function between said first video signal and said second video signal; and

an output stage coupled to said mixing circuit for providing an output signal.

2. The signal mixer of claim 1, wherein the mixing circuit comprises an aperture signal circuit for modifying the parabolic function as a function of an aperture signal.

3. The signal mixer of claim 1, wherein the mixing circuit comprises:

a maximum signal detector for detecting the maximum value of the first video signal or the second video signal;

a minimum signal detector for detecting the minimum value of the first video signal or the second video signal;

a circuit for providing a difference signal comprising the difference between the maximum value of the first video signal or the second video signal and the minimum value of the first video signal or the second video signal;

an aperture circuit responsive to an aperture signal and to the difference signal for providing an aperture varied signal for varying the output signal corresponding to the value of the aperture signal;

a multiplier circuit for squaring the aperture varied signal;

an adder circuit for adding the squared aperture varied signal to the maximum value of the first video signal or the second video signal.

4. The signal mixer of claim 3, wherein the output stage comprises:

an output multiplexer for selecting either the maximum value of the first video signal or the second video signal or the output of the adder circuit to provide said output signal.

5. A signal mixer for mixing a first video signal with a second video signal to produce an output signal while smoothly controlling the rate of change of an output signal, comprising:

a maximum signal detector for detecting the maximum value of the first video signal or the second video signal;

a minimum signal detector for detecting the minimum value of the first video signal or the second video signal;

a circuit for providing a difference signal comprising the difference between the maximum value of the first video signal or the second video signal and the minimum value of the first video signal or the second video signal;

an aperture circuit responsive to an aperture signal and to the difference signal for providing an aperture varied signal for varying the output signal corresponding to the value of the aperture signal;

a multiplier circuit for squaring the aperture varied signal;

an adder circuit for adding the squared aperture varied signal to the maximum value of the first video signal or the second video signal; and

an output multiplexer for selecting either the maximum value of the first video signal or the second video signal or the output of the adder circuit to provide a parabolized output signal.

6. The signal mixer of claim 5, wherein the aperture circuit provides an interim signal comprising the difference between the aperture signal and the difference signal, divided by two, and the multiplier is responsive for squaring the interim signal.

7. The signal mixer of claim 5, wherein the aperture signal varies between zero and one.

8. A method for mixing a first video signal with a second video signal to provide a parabolized output signal while smoothly controlling the rate of change of the output signal, comprising the steps of:

detecting the maximum value of the first video signal or the second video signal;

detecting the minimum value of the first video signal or the second video signal;

determining a difference between the maximum value of the first video signal or the second video signal and the minimum value of the first video signal or the second video signal and providing a first difference signal;

receiving an aperture signal;

determining the difference between the aperture signal and the first difference signal to provide an aperture varied signal;

squaring the aperture varied signal;

adding the squared aperture varied signal to the maximum value of either the first video signal or the second video signal; and

selecting either the maximum value of the first video signal or the second video signal or the output of the adding step, to provide the parabolized output signal.

9. In a video signal color correction system operative for scene-by-scene color corrections, including color correction circuit components for applying color corrections to an input video signal, and circuit components for providing a qualification function for selectively applying color corrections to the input video signal as a function of qualifier parameters, said qualifier parameters operative for applying fractional degrees of color correction at fractional boundaries of qualification regions, the improvement comprising:

a parabolic mixer for mixing video signals including the plurality of qualifier parameters with a parabolic function so as to eliminate discontinuities in regions of the signal which would otherwise produce discontinuities from mixing of the video signals.

10. The improvement of claim 9, wherein the qualifier parameters are selected from the group comprising hue qualification, saturation qualification, and luminance qualification.

11. The improvement of claim 9, wherein the qualifier parameter is a user definable window qualifier.

12. A signal mixer for mixing a first video signal with a second video signal while smoothly controlling the rate of change of an output signal, comprising:

an input stage for receiving the first video signal and the second video signal;

a mixing circuit for mixing the first video signal with the second video signal based on a predetermined parabolic function, wherein the mixing circuit comprises,

an aperture signal circuit for modifying the parabolic function as a function of an aperture signal; and

an output stage for providing a parabolized output signal.

13. The signal mixer of claim 12, wherein the mixing circuit comprises:

a maximum signal detector for detecting the maximum value of the first video signal or the second video signal;

a minimum signal detector for detecting the minimum value of the first video signal or the second video signal;

a circuit for providing a difference signal comprising the difference between the maximum value of the first video signal or the second video signal and the minimum value of the first video signal or the second video signal;

the aperture signal circuit responsive to the aperture signal and to the difference signal for providing an aperture varied signal for varying the output signal corresponding to the value of the aperture signal;

a multiplier circuit for squaring the aperture varied signal;

an adder circuit for adding the squared aperture varied signal to the maximum value of the first video signal or the second video signal.

14. The signal mixer of claim 13, wherein the output stage comprises:

an output multiplexer for selecting either the maximum value of the first video signal or the second video signal or the output of the adder circuit to provide a parabolized output signal.