JPS6155315B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a chromakey signal generating device for the purpose of reproducing high-quality shadows with low noise in a composite screen in a chromakey effect in color television. Conventionally, in the chromakey effect of color television, shadow processing using a soft chromakey signal generator, etc. has been used to reproduce the shadow of the subject projected onto the back panel of the chromakey in the composite screen and create a natural composition. There is a chromakey method. This principle is based on the color camera R.
From the B and G outputs, a normal hard key signal and a soft key signal containing shadow are obtained as a key signal with a hue corresponding to the color of the chroma key back. The signal is linear gated to create a background screen that includes a shadow that corresponds to the shadow of the subject on the chromakey back panel. Further, based on the hard key signal, another gate amplifier is used to synthesize the subject screen on the chroma key back panel and the background screen including the shadow. Generally speaking, lighting in shadow areas is controlled by a gate amplifier in the latter stage, which uses a hard key signal to gate only the subject excluding the shadows, so it is necessary to have a certain level of light, such as a base light, rather than complete blackness. . FIG. 1 shows the configuration of a shadow chromakey system using a typical soft chromakey signal generator of this type. Output R of color camera 2,
The B and G signals enter the hue matrix circuit 3,
A desired hue is selected using the hue dial 4, and signals a and b are obtained. As the signals a and b, for example, a is a B+G/2 signal when the chroma key back color is cyan, and a signal b is an R signal. Next, it enters a subtraction circuit 5 to obtain an a-b color difference signal A, is shaped into a sharp hard key signal by a stretch amplifier 6, and is sent to a gate amplifier 14 as a hard key signal B through a delay circuit 7. On the other hand, the color difference signal A passes through a black clipper 8 that cuts out signals below the black level, and then passes through a gain control circuit 9.
After entering the soft key signal C, the level is adjusted by a level adjuster 10, and the soft key signal C is sent as an output to a linear gate amplifier 13 through a delay circuit 11 and a white clipper 12. Linear gate amplifier 13
A background signal from the color camera 1 is also input to the chroma key back panel, and this signal is linear gated using the soft key signal C to create a shadow that includes a shadow and has the part corresponding to the subject on the chroma key back panel punched out. A background signal is obtained. Furthermore, gate amplifier 1
In step 4, the NTSC signal of the color camera 1, which is imaging the subject on the chroma key back panel, and the above-mentioned shadowed background signal (2) are inserted into the hard key signal (B) to obtain a chroma key composite signal (H) that becomes a complete composite screen. There is. Figure 2 shows these screens, where F corresponds to the output background signal of color camera 1, G corresponds to the output NTSC signal of color camera 2, D corresponds to the shadow background signal, and E corresponds to the chromakey composite signal E. do. The case of color bars will be explained below. Figure 3 shows the color bar waveform when cyan is selected as the hue dial. Figure 3 A to D are the color bar waveforms of B, R, G, and B+G/2, respectively, and E is the waveform of the known color difference signal B+G/2-R when cyan is selected. Corresponds to signal A. Figure 3 shows the waveform of the soft key signal.
In Figure C, Figure 3 G shows the waveform of the hard key signal.
Corresponds to Figure B. Here, the slice point of the soft key signal is normally adjusted to the O level of the color difference signal by the black clipper 8, and the slice point of the hard key signal is adjusted to +50% by the stretch amplifier 6. In addition, the shadow of the cyan panel of the chroma key back is expressed as shadow cyan, and the shadow cyan part of the soft key signal creates a shadow on the background screen, and in the case of the hard key signal, the shadow cyan, that is, the shadow is removed by the above-mentioned slicing effect. , With this hard key signal, only the shadowed background image and the subject excluding the shadow on the chromakey cyan panel are combined. However, the shadow parts of the composite screen inevitably have a lot of noise. This is because a color difference signal of a-b is used, and below, the noise in the shadow part is calculated when a representative cyan color is selected from which a color difference signal of B+G/2-R is obtained. Random noise of color camera output R, B, G each n
Let _R , n _B , n _G be, and the random noise of the color difference signal is

It is expressed by [Formula], and if n _B = n _G = n _R ,

[Formula] becomes approximately 1.2 times more random noise than the camera outputs R, B, and G. The same thing can be said even if you select other colors with Hyudial. As described above, the conventional method has the disadvantage that there is a lot of noise in the shadows of the composite screen and the quality is degraded. SUMMARY OF THE INVENTION An object of the present invention is to provide an apparatus for generating a key signal for reproducing high-quality shadows by eliminating the drawback of increased noise as described above. This key signal will be referred to herein as a shadow key signal to distinguish it from a conventional soft key signal. FIG. 4 shows an embodiment of a typical shadow chromakey signal generating device of the present invention. Its configuration and operation will be explained below. The output R, B, and G signals of the color camera 2 enter a hue matrix circuit 3, and a desired hue is selected by a hue dial 4 to obtain signals a and b. Next, these signals are input to the subtraction circuit 5 to obtain an a-b color difference signal a. Although various combinations of signals a and b can be obtained, one of them may be input as a to the subtraction circuit 5, the other as b, and the difference signal may be obtained in the order of subtracting b from a. This signal is further shaped into a sharp hard key signal by a stretch amplifier 6, and sent to a gate amplifier 14 as a hard key signal through a delay circuit 7. On the other hand, the output a signal of the hue matrix circuit 3 has high frequency noise removed by a low pass filter 8', enters a gain control circuit 9, undergoes level adjustment by a level adjuster 10, and then passes through a delay circuit 10.
1. Pass the white clipper 12 and output the shadow key signal H' to the linear gate amplifier 1.
I am sending it to 3. The background signal from the color camera 1 is also input to the linear gate amplifier 13.
This signal is linear gated using a shadow key signal C' to obtain a background signal D' containing a shadow. Since this background signal is linear gated with a shadow key signal consisting only of the a signal, which is not a color difference signal, the portion corresponding to the subject on the chromakey panel is not completely punched out, resulting in a semi-synthetic screen. Thereafter, in the gate amplifier 14, the object on the chroma key panel and the above-mentioned shadowed background screen are fitted into each other using the hard key signal B, and a chroma key composite signal H, which is a complete composite screen, is obtained. This will be explained using color bars below. FIG. 5 shows the color bar waveform when the hue dial is selected as cyan. Figure 5 A, B, C, D are B, R, G, respectively.
This is a waveform of B+G/2, and E in the figure shows a waveform of a known color difference signal B+G/2-R when cyan is selected. 5 shows the waveform of the shadow key signal, which is the same waveform as B+G/2 shown in 2 of the same figure. FIG. 5 shows a hard key signal that has been shaped using +50% of the color difference signal as a slice point. The shadow key signal creates a shadow on the background screen, but as you can see from the color bar waveform,
When the colors Y and G appear in the subject on the chromakey panel, the background screen becomes a semi-composite screen in which the portion corresponding to the subject is not completely gated. However, this is not a problem because it is ultimately synthesized using the hard key signal. Regarding the random noise in the shadow area,
Since the B+G/2 signal is used as the shadow key signal,

[Formula] When n _B = n _G = n _R , random noise N = √12n _B , which is approximately 0.7 times the camera outputs R, B, and G, resulting in an S/N improvement of approximately 4.7 dB compared to the conventional one. Also,
Since a low-pass filter is used, the noise is actually further reduced. As is clear from the above embodiments, according to the present invention, a high-quality screen can be obtained as a shadow chroma key, and its effects are great.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a conventional chromakey signal generating device, FIG. 2 is an explanatory diagram of its operation, FIG. 3 is a signal waveform diagram thereof, and FIG. 4 is a block diagram of a chromakey signal generating device according to an embodiment of the present invention. , FIG. 5 is a diagram of the signal waveform. 1, 2...Color camera, 3...Hue matrix circuit, 9...Gain control circuit, 10
...Level adjuster, 8'...Low pass filter.

Claims (1)

[Claims] 1. A hue matrix circuit into which the R, B, and G signals from one color television camera are input and the hue can be selected using a hue dial. High-frequency noise is removed from one of the two sets of output signals obtained through this hue matrix circuit. A low-pass filter is provided, and a gain control circuit is provided to adjust the level of the output of the low-pass filter, and while the output signal of the gain control circuit is sent to the linear gate amplifier, the background signal from the other television camera is sent to the gain control circuit. A chromakey signal generating device characterized in that a background key signal including a near-gate tone and low-noise shadow is obtained from an output signal.