Video color detector and chroma key device and method

Claims

We claim:

1. A video color detector device comprising detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including filter means for transmitting only those video signals having a phase angle within a predetermined passband relative to a variable predetermined phase angle, hue selection means for pre-selecting said predetermined phase angle, and passband width control means for varying the width of said passband independently of the saturation of the transmitted signals.

2. A device as in claim 1 including level detector means connected to the output of said filter means to discriminate against output signal levels other than those falling within a predetermined range.

3. A device as in claim 2 in which the magnitude of said video signals is representative of the saturation of the color, and said level detector is adapted to discriminate against signals whose saturation is greater than a predetermined level.

4. A video color detector device comprising detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including filter means for transmitting only those video signals having a phase angle within a predetermined passband relative to a variable predetermined phase angle, hue selection means for pre-selecting said predetermined phase angle, and passband width control means for varying the width of said passband independently of the saturation of the transmitted signals, said device including means for creating at least one barrier to form a window of variable position in a video picture formed from said signals and for disabling said detector when detecting video signals on one side of the barrier forming said window.

5. A device as in claim 4 including means for varying the size of said window.

6. A video color detector device comprising detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including filter means for transmitting only those video signals having a phase angle within a predetermined passband relative to a variable predetermined phase angle, hue selection means for pre-selecting said predetermined phase angle, and passband width control means for varying the width of said passband independently of the saturation of the transmitted signals, in which said video signals include red (R), green (G), and blue (B) component signals, and a luminance (Y) signal, means for forming the signals (R-Y) and (B-Y), and means for modulating said R-Y signal with a signal corresponding to sine .theta. and modulating said (B-Y) signal with a signal corresponding to cos .theta., where .theta. is said predetermined phase angle, subtracting the latter modulation product from the former modulation product, forming signals proportional to D(R-Y) cos .theta. and D(B-Y) sin .theta., where D is a bandwidth factor, adding the latter signals together and rectifying the result, subtracting the result of the rectifying operation from a reference signal and multiplying that result times the result of subtracting the two modulation products from one another, said passband width control means comprising means for varying the value of D.

7. A device as in claim 6 in which said hue selector means comprises means for pre-selecting the angle .theta..

8. A video color detector device comprising detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including electrical circuit means for transmitting only those video signals having phase angles within a relatively narrow passband but having a substantially full range of saturation values.

9. A device as in claim 8 in which a curve representing the variation of the magnitude of the transmitted signals with hue has a substantially spike form.

10. A device as in claim 8 including passband control means for varying the width of said passband independently of saturation values and thereby varying the range of hue detected.

11. A device as in claim 10 including hue selector means for varying the relative position of said passband around a color vector circle to select the predominant hue to be detected.

12. A device as in claim 8 including level detector means connected to the output of said electrical circuit means to discriminate against signals whose saturation is above a predetermined level.

13. A video color detector device comprising detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including electrical circuit means for transmitting only those video signals having phase angles within a relatively narrow passband but having a substantially full range of saturation values, said device including means for creating at least one barrier to form a window of variable position in a video picture formed from said signals and for disabling said detector when detecting video signals on one side of the barrier forming said window.

14. A chroma key device, said device comprising a video color detector for producing a color detection signal, said detector including detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including electrical circuit means for transmitting only those video signals having phase angles within a relatively narrow passband but having a substantially full range of saturation values, and switching means for switching an output circuit from a first video signal source to a second video signal source in response to said color detection signal.

15. A device as in claim 14 passband control means for varying the width of said passband independently of saturation values and thereby varying the range of hues detected.

16. A device as in claim 15 including hue selector means for varying the relative position of said passband around said color vector circle to select the predominant hue to be detected.

17. A device as in claim 14 including level detector means connected to the output of said electrical circuit means to discriminate against signals whose saturation is above a predetermined level.

18. A device as in claim 17 including means for discriminating against signals whose saturation is below a second predetermined level.

19. A chroma key device comprising a video color detector for producing a color detection signal, said detector including detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including electrical circuit means for transmitting only those video signals having phase angles within a relatively narrow passband but having a substantially full range of saturation values, switching means for switching an output circuit from a first video signal source to a second video signal source in response to said color detection signal, and passband control means for varying the width of said passband independently of saturation values and thereby varying the range of hues detected; said device including hue selector means for varying the relative position of said passband around said color vector circle to select the predominant hue to be detected; said device further including a plurality of said color detectors, each being capable of being set to detect a different predetermined hue, said switching means being adapted to respond separately to each color detection signal to switch from one to another of a plurality of video signal sources, whereby multiple key areas can be formed in a single video picture.

20. A chroma key device, said device comprising a video color detector for producing a color detection signal, said detector including detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including filter means for transmitting only those video signals having a phase angle within a predetermined passband relative to a variable predetermined phase angle, hue selection means for pre-selecting said predetermined phase angle, and passband width control means for varying the width of said passband independently of the saturation of the transmitted signals, and switching means for switching an output circuit from a first video signal source to a second video signal source in response to said color detection signal.

21. A device as in claim 20 including level detector means connected to the output of said filter means to discriminate against output signal levels other than those falling within a predetermined range in which the magnitude of said video signals is representative of the saturation of the color, and said level detector is adapted to discriminate against signals whose saturation is above a predetermined level.

22. A chroma key device comprising a video color detector for producing a color detection signal, said detector including detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including filter means for transmitting only those video signals having a phase angle within a predetermined passband relative to a variable predetermined phase angle, hue selection means for pre-selecting said predetermined phase angle, passband width control means for varying the width of said passband independently of the saturation of the transmitted signals, and switching means for switching an output circuit from a first video signal source to a second video signal source in response to said color detection signal, said device including means for creating at least one barrier to form a window of variable position in a video picture formed from said signals and for disabling said detector when detecting video signals on one side of the barrier forming said window.

23. A device as in claim 22 including means for varying the size of said window.

24. A chroma key device comprising a video color detector for producing a color detection signal, said detector including detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including filter means for transmitting only those video signals having a phase angle within a predetermined passband relative to a variable predetermined phase angle, hue selection means for pre-selecting said predetermined phase angle, passband width control means for varying the width of said passband independently of the saturation of the transmitted signals, and switching means for switching the output circuit from a first video signal source to a second video signal source in response to said color detection signal, in which said video signals include red (R), green (G), and blue (B) component signals, and a luminance (Y) signal, means for forming the signals (R-Y) and (B-Y), and means for modulating said R-Y signal with a signal corresponding to sine .theta. and modulating said (B-Y) signal with a signal corresponding to cos .theta., where .theta. is said predetermined phase angle, subtracting the latter modulation product from the former modulation product, forming signals proportional to D(R-Y) cos .theta. and D(B-Y) sine .theta., where D is a bandwidth factor, adding the latter signals together and rectifying the result, subtracting the result of the rectifying operation from a reference signal and multiplying that result times the result of subtracting the two modulation products from one another, said passband width control means comprising means for varying the value of D.

25. A device as in claim 24 in which said hue selector means comprises means for pre-selecting the angle .theta..

26. Apparatus for switching video signals at an output terminal by switching between a first video signal source producing first video signals and a second video signal source producing second video signals, comprising: detecting means for detecting the ones of said first video signals which are within a predetermined range of colors adjacent a variable principal color; first control means for varying said principal color; switching means responsive to said detecting means for switching said output terminal from said first video signal source to said second video signal source when the detected ones of said first video signals are within said predetermined color range; said first video signal source being adapted to reproduce video signals stored on an image storage medium in frames, means for developing frame identification signals for said frames, memory means, means for storing said frame identification signals in said memory means, means for storing data corresponding to the setting of said first control means in said memory for each frame for which it is to be used, and means responsive to said frame identification signals for reading said data out of said memory and applying said data to control the settings of said first control means during reproduction of the images of the corresponding frame.

27. Apparatus as in claim 26 and including second control means for narrowing or widening the response characteristic curve of said detecting means to narrow or widen said range, means for storing data corresponding to the settings of said second control means and means responsive to said frame identification signals for retrieving the latter data and applying it to control the settings of said second control means during reproduction of the images of the corresponding frame.

28. Apparatus as in claim 26 including means for making color corrections for signals from said first source, storing data corresponding to said corrections in said memory, and means responsive to said frame identification signals for retrieving the latter data and applying it to control signals representing the colors of the reproduced images during reproduction of the images of the corresponding frame.

29. Apparatus as in claim 26 including means for adapting said detecting means to operate selectively to perform in color correction or to perform in switching between video sources, and for storing color correction data and/or chroma key control settings data.

30. Apparatus as in claim 26 including level detector means connected to the output of said detecting means to discriminate against output signal levels other than those falling within a predetermined range.

31. Apparatus as in claim 26 including means for creating at least one barrier to form a window of variable position in a video picture formed from said signals and for disabling said detector when detecting video signals on one side of the barriers forming said window.

32. Apparatus as in claim 26 in which said memory means is random access memory means with means for recalling data stored for prior scenes by retrieval based on use of the frame identification information, applying the recalled data to images in a frame currently being analyzed, and modifying the recalled data to the extent necessary to adapt it for use with the current frame.

33. A method of switching video signals at an output terminal by switching between a first video signal source producing first video signals and a second video signal source producing second video signals, said method comprising the steps of:

providing detecting means for detecting signals within a predetermined range of colors;

setting a variable principal color;

narrowing or widening the response characteristic curve of said detecting means, while maintaining a substantially full range of saturation values, to narrow or widen the range of detectable colors adjacent said principal color;

detecting the ones of said first video signals which are within said range of colors adjacent said variable principal color; and

providing switching means responsive to said detecting means for switching said output terminal from said first video signal source to said second video signal source when the detected ones of said first video signals are within said color range.

34. A method as in claim 33 in which said setting step comprises operating a substantially infinitely variable control means for varying said principal color.

35. A method as in claim 33 including the step of limiting the response of said switching means to those signals from said detecting means which are below a predetermined range.

36. A method as in claim 33 including the step of providing a plurality of color detecting means and setting each to detect a different color and to cause switching between different video sources when the corresponding colors are detected.

37. A method of switching video signals at an output terminal by switching between a first video signal source producing first video signals and a second video signal source producing second video signals, said method comprising the steps of:

providing detecting means for detecting signals within a predetermined range of colors;

setting a variable principal color;

narrowing or widening the response characteristic curve of said detecting means to narrow or widen the range of detectable colors adjacent said principal color;

detecting the ones of said first video signals which are within said range of colors adjacent said variable principal color; and

providing switching means responsive to said detecting means for switching said output terminal from said first video signal source to said second video signal source when the detected ones of said first video signals are within said color range;

in which said first video source is a reproduction device for reproducing images stored on a storage medium in frames, said method further including the steps of:

providing memory means, means for developing frame identification signals for said frames, and means for storing said frame identification signals in said memory means;

storing data corresponding to the setting of said first control means in said memory for each frame for which it is to be used;

providing means responsive to said frame identification signals for storing in said memory means data corresponding to the control settings for said detecting means; and

causing the data to be read out under control of the frame identification signals and applied to said detecting means during reproduction of corresponding images.

38. A method as in claim 37 including forming a window in a video picture produced on a monitor from the video signals from said first source, sizing and positioning said window to encompass a desired object, and limiting the action of said detecting means to the area inside or outside of said window.

39. A method as in claim 38 including providing a computer and programming said computer to cause said window to move with the motion of an object it encompasses from one scene or frame to another.

40. A video color detector device comprising detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including filter means for transmitting only those video signals having a phase angle within a predetermined passband relative to a variable predetermined phase angle, hue selection means for pre-selecting said predetermined phase angle, and passband width control means for varying the width of said passband independently of the saturation of the transmitted signals, in which said detecting means includes means for combining quadrature signals proportional to the sine and cosine of an angle corresponding to the color vector to be detected, and including sine wave voltage generator means, and means for sampling said sine wave voltage and storing signals proportional to the voltages of said sine wave at points in the wave separated by ninety degrees in phase to produce said quadrature signals.

41. A video color detector device comprising detecting means for detecting the color phase angle representing the hue of color information-bearing video signals, said detecting means including electrical circuit means for transmitting only those video signals having phase angles within a relatively narrow passband but having a substantially full range of saturation values, in which said detecting means includes means for combining quadrature signals proportional to the sine and cosine of an angle corresponding to the color vector to be detected, and including sine wave voltage generator means, and means for sampling said sine wave voltage and storing signals proportional to the voltages of said sine wave at points in the wave separated by ninety degrees in phase to produce said quadrature signals.

42. A chroma key device, said device comprising a video color detector for producing a color detection signal, said detector including detecting means for detecting the color phase angle representing the hue color information-bearing video signals, said detecting means including filter means for transmitting only those video signals having a phase angle within a predetermined passband relative to a variable predetermined phase angle, hue selection means for pre-selecting said predetermined phase angle, passband width control means for varying the width of said passband independently of the saturation of the transmitted signals, and switching means for switching an output circuit from a first video signal source to a second video signal source in response to said color detection signal, in which said detecting means includes means for combining quadrature signals proportional to the sine and cosine of an angle corresponding to the color vector to be detected, and including sine wave voltage generator means, and means for sampling said sine wave voltage and storing signals proportional to the voltages of said sine wave at points in the wave separated by ninety degrees in phase to produce said quadrature signals.

43. A device as in claim 40 or 41 or 42 including means for producing further signals proportional to the sine and cosine of said angle, each being multiplied by a band width factor D, and being combined with said quadrature signals to give said device a bandwidth proportional to D.

FIELD OF THE INVENTION

This invention relates to devices and methods for detecting the colors represented by video signals, and to devices and methods for selectively connecting an output circuit to a selected one of two or more video signal sources in response to the detection of signals representing a pre-determined color. The latter devices and methods are commonly referred to as "chroma key" devices and methods.

BACKGROUND OF THE INVENTION

Video color detectors have several different uses. The use of color detectors in color correction is described in the above-identified co-pending patent applications. The use of such detectors in chroma keying is described herein.

Chroma key devices and methods typically are used to insert images from one video source into the picture formed by signals from another source. Either of the sources can be any of a variety of different types, e.g., a television camera viewing a "live" scene; a telecine device producing video signals from motion picture film; a video tape player reproducing video signals recorded on magnetic tape or other media; etc.

A typical use of a chroma key device during a live television broadcast is illustrated in FIG. 8 of the accompanying drawings, which shows a video monitor or receiver 200 which displays a video picture 202. A video camera (not shown) views a weather forecaster 204 standing in front of a large vertical blue surface called a "matte" which is not visible in FIG. 8. Instead, wherever the blue matte appears behind the forecaster 204, it has been replaced by the image of a weather map 206 showing the U.S. and parts of Canada and Mexico. The forecaster sees the weather map image on a studio monitor (also not shown in FIG. 8) and points to areas of the matte to indicate areas on the map. The weather map can have superimposed images, such as temperature data, etc.

Video signals forming the weather map are generated by a video source usually referred to as a "background source", and the image of the weather forecaster is generated by the studio camera, which usually is called a "foreground source".

The insertion of a weather map in place of the blue matte is made by a chroma key device which detects the foreground signals from the video camera. When, during each horizontal scan, signals representing the blue color of the matte are detected, the chroma key device switches the broadcast signal from the foreground source to the background source. Then, when the non-blue color of the forecaster is detected, the signals broadcast are switched to the foreground source, and then back again to the background source when the matte is detected again. This process is repeated for each horizontal line in the picture. Thus, the background signal replaces the blue matte everywhere except where the forecaster is located.

A major problem with prior chroma key devices is that they often provide false key signals by responding erroneously to colors other than the matte color. For example, the device often produces key signals upon the detection of not only the blue matte signals, but also the blue eyes or clothing of the announcer. This is very undesirable.

Sometimes the chroma key device will not respond to the matte color. Then the lighting in the television studio or the matte must be changed so that the apparent matte color is just right for the chroma key device. This can be very time-consuming and expensive.

Variation in the matte color to which the chroma key device will respond is provided in some prior art devices by means of a variable hue or color control in which the color or hue to which the keyer will respond can be varied throughout the entire spectrum of visible light. FIG. 7 of the accompanying drawings is a schematic vector representation of the hue and saturation of a given color video signal, as it is shown on the familiar "vectorscope" used in video production equipment. The angle ".theta." of the vector represents the hue or color of the signals, and the length "S" of the vector represents the saturation or intensity of the signals. Although the hue or color control of such prior equipment theoretically makes it possible to select any hue as the matte color by, in effect, making it possible to rotate the vector in FIG. 7 through 360.degree., the keyer using this control actually responds to or "keys" on hues or colors far different from the desired matte color--at least when the colors are at anything less than high saturation levels. In other words, the device does not accurately discriminate among similar colors. This tends to cause false keying in response to other hues appearing elsewhere than in the matte area of the television picture.

The use of highly saturated or intense matte colors tends to somewhat alleviate the above problem, but places severe restraints on the colors usable in the studio, on lighting and other artistic variables, and on the variety of usable matte colors.

The use of prior chroma key devices also places undesirable restraint on the location of the weather reporter or announcer in relation to the matte. When using such prior devices, the announcer should be located at a relatively great distance from the matte so that blue matte color will not be reflected onto the announcer and cause false keying.

The use of bright or saturated blue as a matte color often causes "flare". Furthermore, the announcers usually must be smoothly coifed because the straggling hairs of a bouffant or other hair style with ragged edges sometimes will cause erroneous keying of the chroma key device.

Accordingly, it is an object of the invention to provide a video color detection device and method which are more accurate and flexible in use than in the past. It is a further object to provide a chroma key device and method which alleviate or solve the foregoing problems; a chroma key device and method in which the color to which the device responds can be controlled so as to prevent false switching or insufficient response to a desired color, and in which the color detection is more accurate and flexible than in the past.

It is another object of the invention to make it possible and practical to provide a plurality of different "keys" or insertions in a single television picture by switching among three or more video signal sources, one providing foreground and the others providing background signals for the multiple inserts.

It is a further object to provide a chroma key system and method capable of providing multiple keys in response to hues closely similar to one another.

An additional objective of the invention is to provide a color detection and chroma key device and method in which the degree of discrimination among hues can be adjusted so as to best adapt the operation of the device to the circumstances at hand.

Another object of the invention is to provide an improved hue detection device and method which is compatible with existing keying or switching devices having means for handling other chroma keying problems such as those caused by shadows, and the problem of providing either "soft" or "hard" edges for the key areas by providing either gradual or abrupt transition in switching between video sources, etc. Thus, it is an object to provide a chroma key device with excellent hue discrimination and other known chroma key features.

In accordance with the present invention, the foregoing objects ar satisfied by the provision of a color detection and chroma key d