JPH0347632B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a chromakey device, and particularly to a chromakey device that makes composite images look more natural.

The visual unnaturalness of a composite image formed by chroma keying is caused by various factors. Examples include color fringing where the backscreen color, such as blue, appears on the outline of the foreground in a composite image, and edge fritters where the outline of the foreground flickers. However, even if you look at the composite image with these improvements, it still looks unnatural due to the lack of perspective and shadows. Although the background image is blurred to create a sense of perspective, and the shadow keying is used to add the shadows of objects in the foreground to the background image, it still does not give a sufficiently natural feel. The reason for this is that when shooting the foreground image, to avoid color fringing and edge flicker,
This is because in order to make the illumination as uniform as possible, the objects in the foreground image shine uniformly as a whole, and are combined as they are.

As an example, consider the two scenes shown in FIG. As in the scene shown in Figure 1A, the foreground of the car and the faces of its occupants must be cast by the shadows of objects in the foreground changing in various ways, and the shadows of objects in the foreground changing in various ways. A house as a scenery, etc.
This never happens due to the distance. However, conventional chromakey devices have not given any consideration to the shadows cast on the faces of the automobile and its occupants. Furthermore, the scene shown in Figure 1B consists of a walking person in the foreground and a house in the background. It should be falling, and this shadow should appear, darker on the person and lighter on the building. However, conventional chromakey devices do not produce any such shadows.

FIG. 2 shows the overall configuration of a conventional digital chromakey device. In the same figure, 1 is an input terminal to which foreground video data FG.VID is supplied;
2 is an input terminal to which background video data BG.VID is supplied, and 3 is an output terminal from which composite image video data KYD.VID appears. The foreground image, in which the subject is positioned in front of a blue back screen, is supplied to the key signal generation circuit 4, and the difference from the blue color of the back screen is calculated for each sample data of the foreground video data. A key signal K ₀ is formed. This key signal _K0 is supplied to the key processor 5,
The key signal K ₁ for color cancellation and the key signals K ₂ and K ₃ for the mixer are formed by processing such as slicing at a reference level and adjusting the gain and edge timing of the key signal. The color cancel circuit 6 is for erasing the back color data from the foreground color video data FG.VID, and outputs the video data CAN.VID.
appears.

Further, 7 indicates a mixer to which foreground and background video data are supplied, and the two are combined by cross-fade or the like using the aforementioned key signal _K3 . This mixer 7 is for shadow keying and is not used for normal chroma keying, and the background video data BG.VID is supplied to the mixer 8 as is. As shown in FIG. 3, the mixer 8 includes multipliers 9 and 10 and a phase inversion circuit 11.
and an adder 12. In other words,
The multiplier 9 multiplies the video data CAN.VID from the color cancel circuit 6 and the key signal _K2 and supplies the result to the adder 12.
The background video data BG.VID and the key signal (1-K ₂ ) from the phase inversion circuit 11 are multiplied and supplied to the adder 12, so that the synthesized video data KYD.VID is obtained from the adder 12. has been done.

As described above, conventional chromakey devices do not add changes in light and shadow that would occur in reality, so they have the disadvantage that the composite image looks visually unnatural.

The object of the present invention is to realize a chroma key device in which such drawbacks are eliminated. According to the present invention, a circuit for generating a shadow signal corresponding to a shadow to be superimposed on a composite image is provided.

The superimposed shadow is created by modulating the luminance signal with a shadow signal, but in this case, there are restrictions arising from the nature of the digital color video signal. That is, in a YUV signal system that transmits a digital color video signal in the form of components of Y data and color difference data U and V, each component is defined as shown in the following equation.

Y=0.299R+0.587G+0.114B U=-0.169R-0.331G+0.500B V=0.500R-0.418G-0.082B From the above formula, yellow YL (R=G=1, B=0),
Cyan CY (R=0, G=B=1), Magenta MG
(R=1, B=0, G=1), and the values of Y, U, and V for each color of R, G, and B are determined as follows.

R: Y=0.299, U=0.169, V=0.500 G: Y=0.587, U=-0.331, V=-0.418 B: Y=0.114, U=0.500, V=-0.082 YL: Y=0.886, U= -0.5, V=0.082 CY: Y=0.701, U=0.169, V=-0.5 MG: Y=0.413, U=0.331, V=0.418 Then, on the coordinates with Y on the vertical axis and U on the horizontal axis By plotting each of the above colors, the parallelogram area indicated by 13 in Figure 4A is found, and similarly Y
By plotting each of the above-mentioned colors on coordinates with V as the vertical axis and V as the horizontal axis, the parallelogram area indicated by 14 in FIG. 4B can be found. component Y,
The values of U and V should only be able to move within regions 13 and 14 shown in FIG. Therefore, if the luminance signal Y is simply modulated by a shadow signal in order to add a change in shadow, the result shown in FIG.
As shown in the figure, the sample data at point X may jump out from outside the defined area, causing the color balance to be distorted. Therefore, in the present invention, as shown in FIG. 4C, modulation is performed such that sample data at point X is varied along a broken line 15 connecting the own position and the origin. For example, modulation for changing point X to point X' is performed by reducing both the luminance signal and color difference signal while maintaining the level ratio at point X. In order to realize such modulation, the key signal for each component of the luminance signal and color difference signal may be modulated with a shadow signal.

An embodiment of the present invention will be described below. The mixer 8 in the digital chromakey device shown in FIG. 2 has the configuration shown in FIG. 5. Fifth
In the figure, key signal modulation circuits 16 and 17 are provided as shown surrounded by broken lines. These key signal modulation circuits 16 and 17 each include attenuators 19 and 20 that attenuate the level of the shadow signal SHD from the terminal 18, and the attenuated shadow signal SHD and key signal K ₂ or (1-K ₂ ). multipliers 21 and 22, which are supplied with multipliers 21 and 22;
The modulated key signals appearing at the outputs of 1 and 22 are fed to multipliers 9 and 10. The above-mentioned attenuators 19 and 20 have instruction signals ADJ ₁ and ADJ _2.
is supplied from terminals 23 and 24, so that the density of the shadow can be changed between the foreground image and the background image. The configuration shown in FIG. 5 is provided for each of the luminance data Y and color difference data U and V, and the modulated key signals appearing at the outputs of the key signal modulation circuits 16 and 17 are used in common. Therefore, as shown in FIG. 4C, it is possible to perform modulation such that the position of each sample of video data is changed along the line 15 connecting the original position and the origin. The composite image video data KYD.VID obtained from the mixer 12 is a shadow signal.
It will have a shadow according to the SHD.

As in the scene explained at the beginning (Figure 1A),
If you want to superimpose a shadow only on the foreground, use the instruction signal
The gain G ₁ of the attenuator 19 may be set to (0<G ₁ <1) by ADJ ₁ and ADJ ₂ , and the gain G ₂ of the attenuator 20 may be set to (G ₂ =1).
Furthermore, when it is desired to superimpose shadows on both the foreground and the background, as in the scene shown in _FIG .
(0<G ₂ <1). Along with this, (G ₁
<G ₂ ), it is possible to make the shadow superimposed on the foreground darker than that on the background.

FIG. 6 shows the entire system of one embodiment of the present invention, and 25 indicates a chromakey device having the above-mentioned mixer. Further, a television camera 26 photographs an object located in front of the blue back screen, and its output is digitized for each component to form foreground color video data FG.VID. Further, the background color video data BG.VID is generated from the digital VTR 27, and the television camera 26 and the digital VTR 27 are operated by a common synchronization signal from the synchronization signal generator 28. Considering the case of compositing the scene shown in FIG. 1A, the television camera 26 photographs a car and the person inside the car, and the digital VTR 27 photographs the scenery outside the car through the window of the moving car. The video source is played back as background video data BG.VID. This background video data BG.VID is supplied to the shadow signal generation circuit 29. This shadow signal generation circuit 29 generates a shadow signal SHD by waveform-shaping only the luminance data through a threshold circuit and band-limiting it with a low-pass filter.
generate. According to this shadow signal SHD,
Changing shadows can be superimposed on a moving car and a person inside the car, and even when the scene shown in FIG. 1A is formed as a composite image, it can look more natural. In addition, in Fig. 6,
30 indicates a monitor receiver.

Furthermore, in the case of a fixed shadow that is not related to the content of the image, rather than a moving shadow as described above, a microcomputer can be used to generate the shadow. Also,
Photographing buildings and other scenery using a television camera,
The output luminance signal is waveform-shaped and band-limited through a threshold circuit, as shown in Figure 1B.
It is possible to form shadows caused by the scenery in front of the camera, which is required in scenes such as those shown in .

As can be understood from the above explanation, according to the present invention, the composite image has a shadow that corresponds to the content of the image, so the composite image can be created with a more natural feel than the conventional chromakey device. It can be made into something. Also,
According to this invention, the key signal is modulated by the shadow signal, and each component of the luminance signal and color difference signal is modulated by the modulated key signal, so that the video signal after modulation is shown in FIG. It is possible to prevent going out of the defined area as shown.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram used to explain a conventional chromakey device, FIGS. 2 and 3 are a block diagram of a conventional chromakey device and a partial block diagram thereof, and FIG.
5 is a block diagram of a mixer in an embodiment of the invention, and FIG. 6 is a block diagram showing the overall system configuration of an embodiment of the invention. . 1... Input terminal for foreground video data, 2... Input terminal for background video data, 7, 8... Mixer, 16, 17... Attenuator, 29... Shadow signal generation circuit.

Claims (1)

[Claims] 1 Level control means for controlling the levels of the foreground video signal and the background video signal, each consisting of a luminance signal Y and color difference signals U and V, using a key signal formed based on the foreground video signal; In the chroma key device, the chromakey device includes a synthesizing means for synthesizing the foreground video signal and the background video signal whose level is controlled, and a shadow signal is generated based on a luminance signal Y of the foreground video signal or the background video signal. The level control means includes a shadow signal generation means, a shadow signal level control means for controlling the level of the shadow signal, and a modulation means for modulating the key signal with the shadow signal output from the shadow signal level control means. , based on the output signal of the modulation means, determine the levels of the luminance signal Y and color difference signals U and V that constitute the foreground video signal, and the levels of the luminance signal Y and color difference signals U and V that constitute the background video signal. A chromakey device characterized in that the chromakey device is configured to control each of the chromakey devices.