JPH0413896Y2 - - Google Patents

Description

[Detailed Description of the Invention] [Technical Field of the Invention] This invention relates to a chromakey signal generating device used for screen composition of television broadcasting.

[Technical background of the invention and its problems] As is well known, a chromakey signal generator is used for screen composition in television broadcasting.
This chromakey signal generator generates a key signal for screen composition using the difference in hue.
Based on the RGB signal, R (red), G (green), B (blue), Y (yellow), M (magenta), and C (cyan) signals are generated using a resistor matrix circuit, etc. A key signal is generated by subtracting the two signals and clipping the difference signal with a black clip circuit.

A typical device is a key signal generation circuit for color B shown in FIG. That is, the fourth
In the figure, input terminals 11 to 13 have B and R signals output from a color television camera, respectively.
A G signal is added, and each B, R, and G signal is sent to the B, R, and G points of a matrix circuit 14 having connection points B, M, R, Y, G, and C, respectively. This matrix circuit 14 is composed of resistors R1 to R6 having mutually equal resistance values.
The signal and the Y signal at the Y point are each sent to a subtraction circuit 15. This subtraction circuit 15 subtracts the Y signal from the B signal. Here, the Y signal is a mixture of R and G signals via resistors R3 and R4, and can be expressed as (R+G). Therefore, the output of the subtraction circuit 15 is B-12 (R+G)
It is expressed as This signal is supplied to a black clip circuit 16 and clipped at a predetermined level.
The clip signal obtained here is outputted from the output terminal 17 as a chromakey signal.

Next, in order to facilitate understanding, the case of a general color bar signal will be specifically explained. Figures 5a to 5c show B, R, and G signals applied to points B, R, and G of the matrix circuit 14 shown in Figure 4, respectively.
The color bar signal waveform is shown, and d in the figure shows the signal waveform at the Y point, that is, B-12 (R+G).
When the above signals are supplied to the matrix circuit 14, the subtraction circuit 15 obtains a difference signal as shown in FIG. That is, as is clear from figure e, if the black clip level for the difference signal is adjusted to point a in the figure, that is, 50%, B
A key signal can be generated by a signal.

However, in the conventional method as mentioned above,
If the saturation is less than 50%, no key signal can be obtained. Further, when performing a soft chroma key generation operation, the crack clip level must be adjusted to point b in FIG. As a result, the color selection area of the chroma key expands, and key signals are generated even in the M and C color portions, which adversely affects the key signal for B color. This is illustrated in a color gamut diagram as shown in FIG. 6, and the above problem becomes clearer depending on the positions of the black clip points a and b.

[Purpose of the invention] This invention was made in order to improve the above-mentioned problems, and it is possible to extract the key signal without expanding the color selection area even in a narrow color gamut range and in soft chroma key signal generation operation. The purpose of the present invention is to provide a chroma key signal generation device that can perform the following steps.

[Summary of the invention] That is, the chroma key signal generation device according to the invention inputs first to third primary color signals and generates a first color difference signal and a second color difference signal obtained by subtracting the third primary color signal from the first primary color signal. a color difference signal generation means for generating a second color difference signal obtained by subtracting a third primary color signal from the primary color signal; a squaring circuit for squaring the second color difference signal; and an inverting amplification for inverting and amplifying the output of the squaring circuit. an adding circuit for adding the output of the inverting amplifier circuit and the first color difference signal taken out by the color difference signal generating means; and generating a chromakey signal by clipping at least the negative polarity side of the output of the adding circuit. The invention is characterized in that it is equipped with a black clip circuit.

[Embodiment of the invention] Hereinafter, an embodiment of the invention will be described in detail with reference to FIGS. 1 to 3.

Figure 1 shows its configuration, and shows the input terminal 21
R, G, and B signals from a color television camera are added to .about.23, respectively. input terminal 21,
Both the R and G signals applied to the input terminals 22 and 22 are sent to the first color difference generation circuit 24, and the G and B signals applied to the input terminals 22 and 23 are both sent to the second color difference generation circuit 25.
B sent to the input terminals 23 and 21,
Both R signals are sent to the third color difference generation circuit 26. The first color difference generation circuit has two inputs R, G to R-
G, -(R-G) are generated, and the output terminal L,
Output from M. The second color difference generation circuit generates two signals B-G and -(B-G) from two inputs B and G, and outputs them from output terminals N and O. The third color difference generating circuit generates two signals R-B and -(R-B) from two inputs R and B, and outputs them from output terminals P and Q. The outputs of the color difference generation circuits 24 to 26 are then sent to a selector circuit 27.

This selector circuit 27 selectively outputs six inputs to output terminals R, S, T, and U in response to a selection switching signal from a selection switching circuit 28. The selected output color difference signals from the output terminals R and S are sent to the first mixer 29,
Selected output color difference signals from outputs T, U are sent to a second mixer 30. The two inputs of the first and second mixers 29 and 30 are mixed at a mixing ratio set by the fine control voltage from the mixing ratio adjustment circuit 31, respectively. The output of the first mixer 29 is sent to the adder 32, and the output of the second mixer 30 is squared by the squaring circuit 33, and then the inverting amplifier 3
4, and is further inverted and amplified by gain adjustment circuit 3.
The gain is adjusted in step 5 and sent to the adder 32.
This adder 32 adds two inputs and outputs the result. This added signal is sent to a black clip circuit 36, where it is clipped, and outputted to an output terminal 37 as a key signal.

In the above configuration, key signal generation using a typical B color will be described below with reference to FIGS. 2 and 3. Note that, to simplify the explanation, a case of a general color bar signal will be described here.

First, the input signals R, G, and B are converted into color difference signals by the first to third color difference generation circuits 24 to 26, the selector circuit 27, and the first and second mixers 29 and 30. Here, a signal B-G as shown in FIG. 2a appears at the output terminal V of the first mixer 29, and a signal R as shown in FIG. 2b appears at the output terminal W of the second mixer 30. -G signal appears.

The output RG of the second mixer 30 is sent to a squaring circuit 33 where it is squared. For this reason, the output terminal X of the squaring circuit 33 is
-G) A signal of ² appears, and the negative polarity component becomes the positive polarity component. Furthermore, the output of the squaring circuit 33 (R-
G) ² is sent to the inverting amplifier 34, where it is inverted and amplified with a gain -α. Therefore, the output terminal of the inverting amplifier 34
At X', a signal -α(RG) ² as shown in d of the figure appears. The output of this inverting amplifier -α(R-G)
² has its gain adjusted by the gain adjustment circuit 35, and then
The signal is supplied to an adder 32 and added to the output B-G of the first mixer 29. Therefore, the output terminal Y of the adder 32 is (B-G)-α'(R
-G) ² (where α' is the gain set by the gain adjustment circuit 35) appears. Here, the gain adjustment circuit 35 adjusts the output of the adder 32 so that only the B color portion has positive polarity. The output (B-G)-α'(R-G) ² of the adder 32 is sent to a black clip circuit 36. That is, if the clip level a' of this black clip circuit 36 is set to 0 level, that is, (B-G)-α'(R-
G) If a positive polarity signal with ² ≧0 is extracted, a key signal of B color with low saturation can be obtained from the output terminal Z of the black clip circuit 36, as shown in FIG.

FIG. 3 shows a color gamut diagram for the above case. The dotted line in the figure shows the color gamut boundary line when α=1, and the solid line shows the color gamut boundary line β when α is a predetermined value of 1 or more.
It shows. That is, in the above configuration, even when a soft chroma key generation operation is performed, C and M colors are not generated as key signals, as is clear from the color gamut boundary line β in FIG. Also,
As is clear from a comparison with the color gamut diagram of FIG. 6, it is possible to generate a key signal for soft chroma operation within a narrow color gamut.

Incidentally, the above-mentioned operation is the same in the key signal generation operation for other colors, and can be easily implemented by simply switching the selection output of the selector circuit 27. Further, by variably adjusting the gain adjustment circuit 35, the color gamut range can be changed.

Therefore, the chroma key signal generation device configured as described above can generate a key signal even in a narrow color gamut range and with a low saturation background color, and can significantly reduce chroma key omissions compared to conventional devices. It can be improved.

[Effects of the invention] As detailed above, this invention provides a chroma key signal generation device that can extract key signals within a narrow color gamut and without expanding the color selection area even in soft chroma key signal generation operation. can be provided.

[Brief explanation of the drawing]

FIG. 1 is a block circuit diagram showing an embodiment of the chromakey signal generating device according to the invention, FIGS. 2 and 3 are diagrams for explaining the operation of the same embodiment, and FIG. Block circuit diagrams showing the configuration of the chromakey signal generator, FIGS. 5 and 6
Each figure is a diagram for explaining the operation of a conventional device. 21-23...Input terminal, 24-26...Color difference generation circuit, 27...Selector circuit, 28...Selection switching circuit, 29, 30...Mixer, 31...Mixing ratio adjustment circuit, 32...Addition 33...square circuit, 34...inverting amplifier, 35...gain adjustment circuit, 36...black clip circuit.

Claims (1)

[Scope of utility model registration request] Three different sets of two different primary color signals are extracted from the three primary color signals of a color television camera, and each subtracts one from the other and one from the other.
a color difference generation circuit that takes out color difference signals of the six primary color signals; a selector circuit into which the six primary color difference signals generated by this circuit are introduced; and a selector circuit that selects four primary color difference signals from the introduced signals; A mixing circuit divides the selected four primary color color difference signals into two sets of two, mixes each at a predetermined mixing ratio to obtain first and second color difference signals, and performs a squaring operation on the second color difference signals. and a squaring circuit for obtaining a positive polarity component, an inverting amplifier circuit for inverting and amplifying the output of this squaring circuit, and an adding circuit for adding the output of this inverting amplifier circuit and the first color difference signal obtained by the mixing circuit. and a black clip circuit that clips at least the negative polarity side of the output of the adder circuit to generate a chroma key signal.