JPH035116B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an NTSC digital line soft chromakey device.

Line chromakey is a device that creates a key signal by focusing on the hue component of a certain reference phase of an NTSC video signal, and synthesizes two videos. In addition, soft chroma key means that the key signal created from a certain hue component has a soft slope, and natural screen composition can be realized without unstable flickering at the boundaries of the image.

FIG. 1 shows a conventional analog line soft chromakey device. The NTSC video signal _fN is first supplied to a bandpass filter 11,
Only the color signal is extracted. This signal is transmitted to the demodulator 12
Then, it is demodulated by a subcarrier having a reference phase (for example, a blue phase signal) supplied from the subcarrier generator 13, and a soft key signal _fSK is produced. Further, the subcarrier is a phase shifter 14
The phase of the subcarrier is shifted by 180° in the modulator 15, and this phase-shifted subcarrier is modulated with the softkey signal. This modulated output signal is supplied to a mixer 17 together with the video signal _fN delayed by a predetermined timing in a delay circuit 16, and from this mixer 17, an NTSC video signal f from which a reference hue component, for example, a blue component has been removed, is supplied. _NB is taken out.

By the way, it is difficult to accurately extract color signals using only the bandpass filter 11, which deteriorates the performance of line chromakey devices using analog processing. Furthermore, analog processing inherently has unstable elements, and there is an increasing demand for processing using more stable digital circuits. Furthermore, digital video systems in which video signals are provided as digital signals are becoming a reality, and at that time, there is also a demand to realize chroma keying as digital signals without going through A/D conversion or D/A conversion. . Against this background, it is necessary to replace conventional analog processing with digital processing.
As is clear from FIG. 1, since the chromakey circuit mainly involves modulation and demodulation, it is technically extremely difficult to process this digitally.

The present invention has been made based on the above-mentioned circumstances, and it is an object of the present invention to provide a digital line soft chromakey device that is capable of realizing line soft chromakey using digital signals as they are through digital processing.

An embodiment of the present invention will be described below with reference to the drawings.

In FIG. 2, _fND is an NTSC video signal converted into a digital signal. i.e. analog NTSC
The video signal is sampled at a frequency four times that of the subcarrier to form a digital signal, and the phase timing of this sampling is set to be on the I and Q axes. This digitized NTSC video signal _fND is supplied to the YC separation circuit 21. This separation circuit 21 is composed of a so-called comb filter, which is more accurate than a bandpass filter in the analog system, and accurately separates the accuracy signal and color signal. This separated color signal is supplied to the I and Q separation circuit 22. As mentioned above, since the sampling phase timing is set on the I and Q axes, the I and Q values are obtained by YC separation, and these I and Q values are separated by the I and Q separation circuit 22. Ru. Here, in the case of the analog method, the key signal is created by demodulating the color signal with a subcarrier of a certain reference phase as shown in Fig. 1, but in this invention, the phase detection function that can be expressed by the I, Q signals and the reference phase is used. A color cancel key signal is created by multiplying by chromaticity (chroma level), and this is further amplified to create a soft chroma key signal. That is, the separated I,
The Q signals are supplied to a phase detection circuit 23 and a chromaticity detection circuit 24, respectively. The phase detection circuit 23 is set with the phase detection function that corresponds to digital demodulation. This function is calculated from the I and Q signals by the phase θ
A function is used in which the larger the difference between this phase θ and a certain reference phase, the lower the sensitivity.
If this function is F, then for example, F(θ-)=a・lcot(θ-)l-b...(1) (However, a is a constant that determines the steepness of phase detection, and b is a constant that determines the steepness of phase detection. This is a constant that determines the phase range.) A key signal is created using this function. Further, the chromaticity detection circuit 24 generates a chromaticity signal from the I and Q signals. A color signal whose phase is shifted by θ from the Q axis is given on the I and Q axes as shown in the following equation.

I=csinθ...(2) Q=ccosθ...(3) Here, c is the chromaticity, which is expressed by I, Q in the following equation.
is given as a function of

c=c√ ² + ² …(4) =√ ² + ² …(5) Therefore, the chromaticity signal can be obtained from this.
This chromaticity signal and the key signal are supplied to a multiplier 25 to produce a color cancel signal. In this case, the phase to be canceled is determined by the reference phase. This color cancel signal is supplied to the multiplier 26 together with the key gain signal _GK ,
It is amplified according to the key gain signal _GK . moreover,
This multiplier 26 limits the maximum value and minimum value of the key signal, and outputs a digital soft chroma key signal _fSKD .

On the other hand, the color cancel signal outputted from the multiplier 25 is supplied to a multiplier 28 together with the output signal of the color signal generation circuit 27, where so-called modulation is performed. This modulated output signal is supplied to an adder 30 together with the digital NTSC video signal f _ND which has been delayed by a predetermined timing in the delay circuit 29, and from this adder 30, the digital NTSC video signal f _ND from which the hue component of the reference phase has been removed is supplied. _-B is output.

According to the above configuration, the color signal is digitally separated and extracted from the NTSC video signal, and the phase detection circuit 23 uses this color signal to directly determine the function value for detecting the phase difference from the reference phase to generate the key signal. , this is multiplied by the chromaticity signal to create a soft chroma key signal. Therefore, it is possible to separate color signals more accurately than with analog chromakey, and it is also possible to realize soft chromakey with stable performance.

Further, by approximating demodulation in analog processing using a function based on the cot function and performing modulation by multiplication, all of these processes can be digitally processed.

As described in detail above, according to the present invention, it is possible to provide a digital line soft chromakey device that can realize line soft chromakey as a digital signal by digital processing.

[Brief explanation of the drawing]

FIG. 1 is a block diagram showing a conventional line soft chromakey device, and FIG. 2 is a block diagram showing an embodiment of a digital line soft chromakey device according to the present invention. 21...YC separation circuit, 22...IQ separation circuit,
23... Phase detection circuit, 24... Chromaticity detection circuit,
25, 26, 28...multiplier, 27...color signal generation circuit, 30...adder.

Claims (1)

[Claims] 1. A circuit that digitally separates and extracts a color signal from an NTSC video signal that is a digital signal, a circuit that calculates the phase difference between the separated color signal and a reference phase as a function value, and generates a key signal; and a circuit for generating a chromaticity signal from the separated color signal, and removes the hue component of the reference phase from the NTSC video signal using the chromaticity signal and the key signal. Line soft chromakey device.