Composite video signal combining system

• US 4,292,649 A
• Filed: 02/14/1980
• Issued: 09/29/1981
• Est. Priority Date: 02/12/1979
• Status: Expired due to Term

• Current Assignee: Telediffusion De France SA
• Original Assignee: Telediffusion De France SA
• Inventors: Macheboeuf, Guy R.
• Primary Examiner(s): Martin, John C.
• Application Number:
  US06/121,779
• Time in Patent Office: 593 Days
• Field of Search: 358/22, 358/183
• US Class Current: 348/587
• CPC Class Codes: H04N 9/75 Chroma key

Abstract

The system combines first and second composite video signals into a resulting composite video signal. The first composite video signal represents a foreground scene having a first trichromatic moving picture region which envelopes a second trichromatic backing region through a trichromatic transition region. The second composite video signal represents a background scene. A gain controlling circuit produces from first component video signals first and second analog signals (1-α), (α) which control in proportion the amplifications of the first and second composite video signals to obtain second output composite video signals. The first analog signal has first and second levels when the first component video signals are representative of the first and second picture regions and has intermediate levels lying between the first and second levels when the first component video signals are representative of the transition region. A video mixer mixes the first and second output composite video signals into the resulting composite video signal.

Claims

1. A system for combining first and second composite video signals into a resulting composite video signal, said first composite video signal representing a first color picture having a first trichromatic region envelopping a second trichromatic region through a trichromatic transition region and said second composite video signal representing a second color picture, said system comprising:

first input means for receiving said first composite video signal;

second input means for receiving said second composite video signal;

third input means for receiving first component video signals forming said first composite video signal;

means connected to said third input means for producing a first analog signal (1-α

) and a second analog signal (α

) which control the crossing of said first and second composite video signals through said first and second input means to provide first and second output composite video signals which are obtained from an amplification with a gain proportional to said first and second analog signals,

said first analog signal having first and second levels when said first component video signals are representative of said first and second picture regions and having intermediate levels lying between said first and second levels when said first component video signals are representative of said transition region; and

means for mixing said first and second output composite video signals into said resulting composite video signal.

2. A system for combining first and second composite video signals into a resulting composite video signal, said first composite video signal representing a first color picture having a first trichromatic region envelopping a second trichromatic region through a trichromatic transition region and said second composite video signal representing a second color picture, said system comprising:

first input means for receiving said first composite video signal;

second input means for receiving said second composite video signal;

third input means for each receiving one of first component video signals forming said first composite video signal;

means each connected to one of said third input means for producing a primary analog signal having first and second levels when the corresponding first component video signal is representative of said first and second picture regions and having intermediate levels lying between said first and second levels when said corresponding first component video signal is representative of said transition region;

analog means for multiplying said primary analog signals into a gain controlling signal α

which controls the crossing of said second composite video signal through said second input means to provide a second output composite video signal which is obtained from an amplification with a gain proportional to said controlling signal α

;

analog means for reversing said gain controlling signals α

into a reversed gain controlled signal (1-α

) which controls the crossing of said first composite video signal through said first input means to provide a first output composite video signal which is obtained from an amplification with a gain proportional to said reversed gain controlling signal (1-α

); and

means for mixing said first and second output composite video signals into said resulting composite video signal.

3. A system according to claim 2, wherein said first and second input means are variable gain amplifiers which are controlled by said reverse gain controlling signal (1-α

) and said gain controlling signal α

, respectively.

4. A system according to claim 2, wherein said analog multiplying means is an analog AND-gate, the inputs of which receive said primary analog signals.

5. A system for combining first and second composite video signals into a resulting composite video signal, said first composite video signal having a first trichromatic region envelopping a second trichromatic region through a trichromatic transition region, each of first component video signals forming said composite video signal which represents said first region, having its amplitude lying outside a first range of reference voltages and each of said first component video signals which represents said second region, having its amplitude lying inside a second range of reference voltages, said transition region being defined by picture points having component video signal amplitude inside two transition voltage ranges boundered by said first and second voltage ranges, respectively, said system comprising:

first input means for receiving said first composite video signal;

second input means for receiving said second composite video signal;

third input means for each receiving one of said first component video signals;

means each connected to one of said third input means for producing a primary analog signal having a first level when the amplitude of the corresponding first component video signal does not lie within said corresponding first voltage range, a second level when said amplitude of said corresponding first component video signal lies within said corresponding second voltage range and intermediate levels lying between said first and second levels when said amplitude of said corresponding first component video signal lies within one of said two transition voltage ranges boundered by said corresponding first and second voltage ranges, each of said intermediate levels being practically linear relationship with the ratio between said corresponding first component video signal amplitude and one of the voltage limits of said transition voltage range including said amplitude;

analog means for multiplying said primary analog signals into a gain controlling signal α

which controls the crossing of said second composite video signal through said second input means to provide a second output composite video signal which is obtained from an amplification with a gain proportional to said gain controlling signal α

;

analog means for reversing said gain controlling signal α

into a reversed gain controlled signal (1-α

) which controls the crossing of said first composite video signal through said first input means to provide a first output composite video signal which is obtained from an amplification with a gain proportional to said reversed gain controlled signal (1-α

); and

means for mixing said first and second output composite video signals into said resulting composite video signal.

6. A system according to claim 5, wherein each of said primary analog signal producing means comprises:

two variable gain amplifiers, each of which having a first input at one voltage limit of one of said two transition voltage ranges in accordance with the corresponding first component video signal and a second input receiving said corresponding first component video signal, and the gain of each of said two variable gain amplifiers varying practically linearly with the amplitude of said corresponding first component video signal when said amplitude lies within said transition voltage range associated with said amplifier, and

primary analog means for multiplying the outputting signals from said variable gain amplifiers into said primary analog signal.

7. A system according to claim 6, wherein each of said primary analog signal producing means comprises means for adjusting said voltage limits applied to said first inputs of said variable gain amplifiers.

8. A system according to claim 6, wherein said primary analog multiplying means in an analog AND-gate having its two inputs connected to outputs of said two variable gain amplifiers.

9. A system for combining first and second composite video signals into a resulting composite video signal, said first composite video signal representing a first color picture having a first trichromatic region envelopping a second trichromatic region through a trichromatic transition region and said second composite video signal representing a second color picture, said system comprising:

first input means for each receiving one of first component video signals forming said first composite video signal;

second input means for receiving one of second component video signals forming said second composite video signal;

means each receiving one of said first component video signals for producing a first analog signal having first and second levels when the corresponding first component video signal is representative of said first and second picture regions and having intermediate levels lying between said first and second levels when said corresponding first component video signal is representative of said transition region;

first analog means for multiplying said first analog signals into a second analog signal;

means receiving said second analog signal for producing a logic signal having said first level when said second analog signal is at said first level and having said second level when said second analog signal is at said second level or at an intermediate level;

second analog means for each multiplying one of said first analog signals by said logic signal into a third analog signal which controls the crossing of the corresponding second component video signal through the corresponding second input means to provide a second input component video signal which is obtained from an amplification with a gain proportional to said third analog signal;

analog means for each reversing one of said third analog signals into a reversed analog signal which controls the crossing of said corresponding first component video signal through the corresponding first input means to provide a first output component video signal which is obtained from an amplification with a gain proportional to said reversed analog signal; and

means for mixing said first and output component video signals into said resulting composite video signal.

10. A system according to claim 9 wherein said first and second input means are variable gain amplifiers which are controlled by said reverse analog signals and said third analog signals, respectively.

11. A system according to claim 9, wherein said first analog multiplying means is an analog AND-gate, the inputs of which receive said first analog signals.

12. A system according to claim 9, wherein each of said second analog multiplying means is an analog AND-gate, two inputs of which receive said logic signal and the corresponding first analog signal.

13. A system for combining first and second composite video signals into a resulting composite video signal, said first composite video signal having a first trichromatic region envelopping a second trichromatic region through a trichromatic transition region, each of first component video signals forming said first composite video signal which represents said first region, having its amplitude lying outside a first range of reference voltages and each of said first component video signals which represents said second region, having its amplitude lying inside a second range of reference voltages, said transition region being defined by picture points having component video signal amplitude inside two transition voltage ranges boundered by said first and second voltage ranges, respectively, said system comprising:

first input means for each receiving one of said first component video signals;

second input means for each receiving one of second component video signals forming said second composite video signal;

means each receiving one of said first component video signals for producing a first analog signal having a first level when the amplitude of the corresponding first component video signal does not lie within said corresponding first voltage range, a second level when said amplitude of said corresponding first component video signal lies within said corresponding second voltage range and intermediate levels lying between said first and second levels when said amplitude of said corresponding first component video signal lies within one of said two transition voltage ranges boundered by said corresponding first and second voltage ranges, each of said intermediate levels being practically linear relationship with the ratio between said corresponding first component video signal amplitude and one of the voltage limits of said transition voltage range including said amplitude;

first analog means for multiplying said first analog signals into a second analog signal;

means receiving said second signal for producing a logic signal having said first level when said second analog signal is at said first level and having said second level when said second analog signal is at said second level or at an intermediate level;

second analog means for each multiplying one of said first analog signals by said logic signal into a third analog signal which controls the crossing of the corresponding second component video signal through the corresponding second input means to provide a second output component video signal which is obtained from an amplification with a gain proportional to said third analog signal;

analog means for each reversing one of said third analog signal into a reversed analog signal which controls the crossing of said corresponding component video signal through the corresponding first input means to provide a first output component video signal which is obtained from an amplification with a gain proportional to said reversed analog signal; and

means for mixing said first and output component video signals into said resulting composite video signal.