JPH05336539A - Method and device for key signal generation - Google Patents

Abstract

PURPOSE:To prevent a foreground and a background part from being misjudged even if an input image has unevenness, dirt, shade, etc. CONSTITUTION:Optimum upper-limit and lower-limit values of small areas obtained by dividing a video signal are calculated on the basis of maximum frequency levels of brightness signals and color difference signals by the small areas which are calculated by a maximum value calculating circuit 3, the frequencies of key-ON operation of the small areas which are calculated by a key-ON pixel quantity calculating circuit 5, and an upper-limit and a lower-limit value which are generated by an initial parameter generating circuit 6; and a 2nd color discriminating circuit 8 performs color discrimination processing by the small areas by using the optimum upper-limit and lower-limit values and the result is used as a key signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a key signal generation method and apparatus for extracting a specific portion of a video signal and outputting the extraction result as a key signal, such as a television signal switcher.

[0002]

2. Description of the Related Art Conventionally, a process of extracting a specific part of a video signal as a key signal and using the key signal to combine two video signals to form one video signal is called a key combining process. It is used as video signal synthesis processing.
Among them, the process of extracting a specific color portion of a video signal as a key signal and using the key signal to combine two video signals to form one video signal is called a chroma key composition process and is widely used. There is. The process of extracting a specific portion of the video signal as a key signal is called a key generation process.

In the conventional chroma key device, a key signal is generated in the entire input image using a constant parameter. Such a key signal generation method using a constant parameter for the entire image is described in, for example, the Technical Report of the Television Society of Japan, Vol. 12, No. 23, pp. 25-28.

FIG. 5 shows the configuration of a conventional chroma key signal generator. In FIG. 5, 901 is a luminance signal input terminal, 902 is a color difference signal RY input terminal, 903 is a color difference signal BY input terminal, 904, 905 and 906 are upper and lower limit value setting circuits, and 907, 908 and 909 are windows. -Comparator, 910 is an AND circuit, and 911
Is a key signal output terminal.

Next, the operation of the above conventional example will be described.
In FIG. 5, a luminance signal input terminal 901 and a color difference signal R-
Y input terminal 902 and color difference signal BY input terminal 903
A luminance signal (Y), a color difference signal (RY), and a color difference signal (BY) in the input video signal are input to each. The upper / lower limit value setting circuit 904 sets and outputs the upper limit value and the lower limit value of the background color for the luminance signal (Y). In the window comparator 907, the upper / lower limit value setting circuit 90
Key-on is output for luminance signals within the range between the upper limit value and the lower limit value input from 4, and key-off is output for other luminance signals. In this way, the window comparator 907 outputs the key signal relating to the luminance signal.
Similarly, the window comparator 908 outputs a key signal relating to the color difference signal (RY), and the window comparator 909 outputs a key signal relating to the color difference signal (BY). These three types of key signals are combined by the AND circuit 910 and output from the output terminal 911.

FIG. 6 is a waveform diagram showing how keys are generated in the conventional example. Here, a waveform of one line of the input video signal is shown. FIG. 6A shows a luminance signal (Y), FIG. 6B shows a color difference signal (RY), and FIG. 6C.
Indicates a color difference signal (BY). These key signals are generated and output as the common part (the part indicated by S in FIG. 6D).

As described above, in the above-described conventional key generation device, the color identification circuit as described above can generate the specific region (specific color) of the input video signal as the key signal.

[0008]

However, in the above-described conventional key signal generation device, since the key signal is generated using the same upper limit value and the same lower limit value for the entire input image, unevenness may occur in the background portion of the input image. When there is dirt or there is a dark part due to the shadow of the subject, in order to generate the background part completely as the key signal ON, part of the originally foreground part is erroneously recognized as the background and the key signal is generated. Or
On the contrary, in order to completely turn off the key signal in the foreground part, a part of the originally background signal is erroneously recognized as the foreground and a key signal is generated.

Regarding the erroneous recognition mentioned here, FIGS.
Will be described with reference to. FIG. 7 shows an example of the input video signal. In FIG. 7, a quadrangle represented by a dotted line is used to divide an input image for convenience of description and is not a signal included in an actual input image. Here, it is assumed that only the color difference signal is used to generate the key signal. FIG. 8 is a distribution diagram (histogram) of color difference signal levels in the small area A (area including the foreground and background) in FIG. In FIG. 3, portions D and F represent the color difference signal levels of the foreground portion such as face and hair. The portion E represents the background portion.

9 and 10 are distribution diagrams (histograms) of the color difference signal levels in the small regions B and C (regions only of the background) in FIG. The small areas B and C are both background portions, but the reason why the distributions of the two areas differ greatly is that there is illumination unevenness in the background portion of the input image. Here, it is assumed that the upper and lower limit values of the color difference signals are set in accordance with the small area A shown in FIG. The upper and lower limit values set at this time are shown by dotted lines in FIGS. 8, 9 and 10. That is, the pixel having the color difference between the dotted lines is recognized as the background portion and the key is turned on. At this time, in the small area A, only the background portion is completely key-on as shown in FIG. 8, and there is no erroneous recognition. However, in the small areas B and C, as shown in FIG.
As shown in parts G and J of FIG. 10, the part that is originally the background is not recognized as the background, and the key is turned off.

The present invention solves such a conventional problem, and is an excellent key signal generation device capable of satisfactorily generating a key signal even for a video signal having background unevenness, stains, shadows and the like. It is intended to provide.

[0012]

In order to achieve the above object, the present invention divides an input video signal into small areas, calculates a signal level distribution of the small areas, and uses the signal level distribution. The optimum parameter for the key signal of the small area is calculated, and the key signal of the small area is generated using the optimum parameter.

[0013]

According to the present invention, the key signal is generated by calculating the optimum parameter for each small area obtained by dividing the video signal, so that the background portion of the input video is free from unevenness, stains, shadows and the like. Even if there is, a good key signal can be generated.

[0014]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. FIG. 1 is a diagram showing the configuration of an embodiment of a key signal generation device according to the present invention.

In FIG. 1, 1 is a video signal input terminal, 2
Is a level distribution calculation circuit, 3 is a maximum value calculation circuit, 4 is a first
Color identification circuit, 5 is a key-on pixel number calculation circuit, 6 is an initial parameter generation circuit, 7 is an optimum parameter calculation circuit, 8
Is a second color identification circuit, and 9 is a key signal output terminal.

Next, the operation of the above embodiment will be described with reference to FIGS. 2 to 4 and 7 to 10. In this embodiment, a quadrangle divided by a dotted line in FIG. 7 is defined as a small area.

First, the operation of the level distribution calculation circuit 2 will be described. The level distribution calculation circuit 2 calculates the histogram distribution of the luminance signal and the color difference signal for each small area shown in FIG. 7 for the color video signal input from the video input terminal 1. Examples of distribution calculation results of the color difference signals of the small areas A, B, and C are shown in FIGS. 8, 9, and 10.

Subsequently, the maximum value calculating circuit 3 calculates the signal level having the maximum frequency from the histograms of the luminance signal and the color difference signals calculated by the level distribution calculating circuit 2. The calculation results in the examples shown in FIGS. 8, 9, and 10 are RefH _A , RefH _B , and RefH, respectively.
It is _C. Where RefH _A , RefH _B , and Re
The values of fH _C differ from each other because the background portion of the input video signal has unevenness.

Next, the initial parameter setting in the initial parameter generating circuit 6 will be described. The parameters set by the initial parameter generation circuit 6 are the upper limit value and the lower limit value for the luminance signal and the color difference signal set by the conventional upper and lower limit value setting circuit. The setting here is performed by focusing on the small area A in FIG. 7 as in the conventional example. That is, the upper limit value and the lower limit value generated by the initial parameter generation circuit 6 are shown by the dotted lines in FIG. The same upper and lower limit values are shown by dotted lines in FIGS. 9 and 10.

The first color identification circuit 4 uses the luminance signal generated by the initial parameter generation circuit 6 and the upper limit value and the lower limit value of the color difference signal to discriminate the color of the video signal input from the video input terminal 1. Processing is performed to generate a key signal. The color identification processing here is the same as the conventional example.

The key-on pixel calculation circuit 5 calculates the number of pixels key-on in the first color identification circuit 4 for each small area.

In the optimum parameter calculating circuit 7, the luminance signal of the small area calculated by the maximum value calculating circuit 3, the maximum frequency level of the color difference signal, the number of key-on pixels of the small area calculated by the key-on pixel number calculating circuit 5, Then, the optimum upper and lower limits of the small area are calculated from the upper and lower limits generated by the initial parameter generation circuit 6. Here, the operation of the optimum parameter calculation circuit 7 will be described by taking a color difference signal as an example. Ref is the maximum luminance frequency level in the small area, N _{KON is} the number of key-on pixels,
The initial parameter upper limit value is L _U , the lower limit value is L _L , the optimum parameter upper limit value is L _ADVU , and the optimum lower limit value level is L _ADVL . At this time, the optimum parameters L _ADVU and L _ADVL are determined as follows.

Ref _INT = (L _U -L _L ) / 2 Condition 1: | Ref-Ref _INT | <TH _Ref Condition 2: N _KON > TH _Key where TH _Ref and TH _Key are appropriate threshold values. ..

If the above conditions 1 and 2 are both satisfied, L _ADVU = L _U + (Ref-Ref _INT ) L _ADVL = L _L + (Ref-Ref _INT ), and otherwise. , L _ADVU = L _U L _ADVL = L _L. The results of the above-described optimum parameter calculation processing performed on the small area A, the small area B, and the small area C are shown in FIGS. 2, 3, and 4, respectively. 2, 3, and 4
It is understood that there is no erroneous recognition portion corresponding to the portions G and J in FIGS. 9 and 10. The above-described optimum parameter calculation process is similarly performed for the luminance signal.

Finally, the second color identification circuit 8 performs the color identification processing in which the upper and lower limits are optimized for each small area by using the optimal upper limit value and the optimal lower limit value calculated by the optimal parameter calculation circuit 7. Be seen. Then, the identification result is output from the key signal output terminal 9 as a key signal.

As described above, in the above embodiment, the optimum parameter is calculated from the maximum frequency level in the small area, the key-on pixel and the initial parameter, and the color identification processing is performed by changing the parameter for each small area. It is possible to generate keys without recognition.

In the above embodiment, the level distribution calculation circuit 2 and the maximum value calculation circuit 3 are used to calculate the optimum parameter. However, the average value calculation circuit calculates the average value of the small area, and May be changed to the maximum level value.

Further, in the above embodiment, the level distribution is calculated for the pixels of the entire small area, but only the pixels which are key-on in the first color identification circuit 4 may be calculated.

Further, in the optimum parameter calculation circuit 7 of the above embodiment, when either of the above conditions 1 and 2 is not satisfied, the upper limit value and the lower limit value generated by the initial parameter generation circuit 6 are set as the optimum parameters. However, the weighted average value of the optimum parameters in the neighborhood area may be used as the optimum parameter.

In the above embodiment, the luminance signal and the color difference signal are used as the input video signal, but this may be another video signal such as an RGB signal.

[0031]

As is apparent from the above embodiment, the present invention divides the input video signal into small areas, calculates the signal level distribution of the small areas, and uses the signal level distribution to calculate the small area. By calculating the optimum parameter for the key signal of the area and generating the key signal of the small area using the optimum parameter, unevenness in the background portion in the input image,
Even if there are stains, shadows, etc., it is possible to prevent erroneous determination of the foreground and background portions and generate an appropriate key signal.

[Brief description of drawings]

FIG. 1 is a block diagram of a key signal generator according to an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a small area A in FIG. 7 and upper and lower limit values in this embodiment.

FIG. 3 is an explanatory diagram showing a small area B in FIG. 7 and upper and lower limit values in this embodiment.

FIG. 4 is an explanatory diagram showing a small area C in FIG. 7 and upper and lower limit values in this embodiment.

FIG. 5 is a block diagram of a conventional key signal generation device.

FIG. 6 is an explanatory diagram of a key generation process in a conventional key signal generation device.

FIG. 7 is an explanatory diagram showing an example of an input video signal and a small area.

8 is an explanatory diagram showing a histogram of a small area A in FIG. 2 and upper and lower limit values in a conventional example.

9 is an explanatory diagram showing a histogram of a small area B in FIG. 2 and upper and lower limit values in a conventional example.

10 is an explanatory diagram showing a histogram of a small area C in FIG. 2 and upper and lower limit values in a conventional example.

[Explanation of symbols]

 2 Level distribution calculation circuit 3 Maximum value calculation circuit 4 First color discrimination circuit 5 Key-on pixel number calculation circuit 6 Initial parameter generation circuit 7 Optimal parameter calculation circuit 8 Second color discrimination circuit

Claims (8)

[Claims] 1. An input video signal is divided into small regions, a signal level distribution of the small regions is calculated, and an optimal parameter for a key signal of the small regions is calculated using the signal level distribution, A key signal generation method for generating a key signal in the small area using the optimum parameter. 2. The key signal generating method according to claim 1, wherein a signal level that gives the maximum frequency of the small region is calculated using a signal level distribution of the small region, and the optimum parameter is calculated using this signal level. 3. A key signal of a specific color portion is calculated from a video signal, the number of pixels in which the key signal is turned on or off in a small area is calculated, and a signal level and a pixel number which give the maximum frequency of the small area 3. The key signal generating method according to claim 2, wherein the optimum parameter is calculated by using. 4. A key signal of a specific color portion is calculated from an input video signal, and an average signal level of a portion in which the key signal is turned on or off in a small area obtained by dividing the video signal is calculated, A key signal generation method for calculating an optimum parameter of the small area using the average signal level and generating a key signal of the small area using the optimum parameter. 5. A means for calculating a signal level distribution for each partial area of a video signal, a means for calculating an optimum parameter for each partial area for generating a key signal, and a key signal for each partial area of the video signal. And a key signal generating device. 6. The key signal generation device according to claim 5, further comprising means for calculating a signal level which gives the maximum frequency of the partial area of the video signal. 7. An identification means for calculating a key signal of a specific color portion from a video signal, and a means for calculating the number of pixels at which the key signal is turned on or off in the partial area of the video signal. Key signal generator. 8. A first identifying means for calculating a key signal of a specific color portion from a video signal, and a circuit for calculating an average signal level of pixels in which the key signal is turned on or off in a partial area of the video signal. A key signal generating device comprising means for calculating an optimum parameter for each partial area of the video signal for generating a key signal, and second identifying means for generating a key signal for each partial area of the video signal.