JPH0496595A - Video signal processing circuit - Google Patents

Abstract

PURPOSE:To facilitate digital color demodulation and to obtain excellent picture quality with no adjustment by A/D-converting a video signal and reproducing the data of a chrominance subcarrier with the sampling theorem from the data of a burst signal part in a digital way. CONSTITUTION:An A/D converter circuit 13 uses a sampling clock D so as to apply A/D conversion to a video signal A and outputs a digital video signal E, an effective video area data in the video signal E is written by one line in a video data line memory 14, a burst signal area data is inputted to a chrominance subcarrier signal recovery circuit 15, which extracts optionally consecutive two-point data by using the sampling clock D, the chrominance subcarrier wave signal G is reproduced as a digital signal by the sampling theorem and written in a chrominance subcarrier line memory 16. Then A video data F from the memory 14 is subject to Y/C separation by a digital comb-line filter 18, separated into a luminance signal data K and a chrominance signal data J, and the chrominance signal data J is demodulated into a color difference signal based on a chrominance carrier data H from the memory 16 at a chrominance signal demodulation circuit 19.

Description

[Detailed Description of the Invention] [Industrial Application Field] This invention relates to a video signal processing circuit that separates Y/C from a video signal, and in particular improves the color demodulation method after A/D conversion in direct encoding. Regarding.

[Conventional technology] When processing video signals, there are basically two methods.

One is to separate the video signal in analog Y/C and then A/D.
The other is a direct encoding method in which the video signal is directly A/D converted and then digitally separated into Y/C.

The former has the advantage of having a degree of freedom in selecting the sampling frequency, while the latter has the advantage that it is easy to perform stable Y/C separation, easy to perform adaptive separation, and requires fewer A/D conversion circuits.

The meanings of the symbols used below are as follows.

FH: Horizontal synchronization frequency W: Bandwidth of luminance signal FS: Sampling frequency (sampling clock) that is more than twice the bandwidth W fsc: Color subcarrier frequency By the way, the sampling frequency F8 of the A/D conversion circuit is the horizontal synchronization frequency The bandwidth W of the luminance signal is an integer multiple of FH
is set to more than twice that of In the direct encoding method,
Further, the sampling frequency FS is often selected to be an integral multiple of the chrominance subcarrier frequency f5°, ie, F'5=nfSC, in order to eliminate beat interference of brightness and chromaticity appearing on the screen. Usually, n=
You can choose 4. In this way, when the sampling frequency F8 is an integral multiple of the color subcarrier frequency fsc,
There was no particular problem because it was easy to reproduce the color subcarrier frequency fsc using hardware.

However, in order to unify the different sampling frequency FS standards for NTSC and PAL systems, an international standard has recently been recommended that sets the basic sampling frequency FS to 13.5MHz for both NTSC and PAL systems. . However, this value is not an integral multiple of the color subcarrier frequency fsc.

If the sampling frequency FS is not an integral multiple of the color subcarrier frequency fsc, a problem arises in that it is difficult to reproduce f8° and color demodulation cannot be easily performed.

For example, FIG. 2 shows a conventional video signal circuit that implements this using a direct encoding method.

A horizontal synchronizing signal is separated from the analog video signal by a synchronizing signal separation circuit 21, and a sampling clock synchronized with this horizontal synchronizing signal is generated in a P, LL circuit 22.

Using this sampling clock, the A/D conversion circuit 23 performs A/D conversion of the video signal, and outputs a digital video signal.

In addition, the analog video signal is already connected to the PLL circuit 24.
Here, only the burst signal is taken in by the BFP signal, from which the color subcarrier frequency fsc is extracted, and this color subcarrier frequency fsc is further transmitted to another A/D.
It is A/D converted by the conversion circuit 25 and output as reference color subcarrier data.

Next, the digital video signal is digitally separated into Y/C by a comb filter 26 and separated into a luminance signal Y and a color signal C. The color signal C is further demodulated in a color signal demodulation circuit 27 into a color difference signal I or BY and a color difference signal Q or RY using the color subcarrier data as a reference.

In this way, in order to extract the color subcarrier frequency fSC from the video signal and obtain the color subcarrier data, the PLL circuit 24 and the A/D conversion circuit 25, which were not required when the signal is an integral multiple, are newly required. , the circuit becomes expensive and complicated.

For this reason, when the sampling frequency is not an integral multiple of the color subcarrier frequency, a separate coding method is adopted in which the sampling frequency can be freely selected regardless of the color subcarrier frequency. That is, as shown in FIG. 3, the video signal processing circuit of the conventional separation encoding method separates the video signal into a luminance signal Y and a color signal C by Y/C using a comb filter 31 while keeping it as an analog signal. Roughly, the C signal is demodulated into color difference signals ■ and Q, or R-Y and B-Y by the color signal demodulation circuit 32, and then Y,
Each of I, Q or Y, R-Y, and B-Y was converted into a digital signal.

[Problems to be Solved by the Invention] However, in the conventional circuit that employs the above-mentioned separation encoding method, due to the performance of the analog comb filter 31,
In addition to having a large effect on image quality, the analog circuitry is large, with three circuits including the comb filter 31, color demodulation circuit 32, and A/D conversion circuits 33, 34, and 35, and there are many adjustment points. Furthermore, there is a problem in that changes over time become large.

The purpose of this invention is to eliminate the above-mentioned problems of deterioration in image quality due to the performance of analog comb filters and an increase in the number of adjustment points due to the expansion of analog circuits. The object of the present invention is to provide a video signal processing circuit that employs a direct encoding method and is inexpensive and simple.

[Means for Solving the Problems] This invention directly A/D converts an analog video signal and then performs Y/C separation using a digital filter.
It is applied to a direct encoding video signal processing circuit that demodulates a color difference signal from a signal.

A color subcarrier signal reproducing circuit that reproduces a color subcarrier signal from an A/D converted burst signal based on a sampling theorem, a video data memory that stores video data from an A/D converted digital video signal, and a reproduction circuit. A color subcarrier memory stores color subcarrier data from the digital color subcarrier signal obtained, video data is stored in a video data memory, and the video data is stored in the color subcarrier memory via a color subcarrier signal reproducing circuit. It is equipped with a timing generation circuit that synchronizes with the color subcarrier data, and demodulates the color difference signal from the C signal obtained by separating it with a digital filter based on the color subcarrier data stored in the color subcarrier memory. This is what I did.

[Operation: Since the color subcarrier frequency is reproduced based on the sampling theorem from the data of the burst signal part of the A/D converted video signal, the sampling frequency at the time of A/D conversion is equal to the bandwidth of the luminance signal. If it is twice or more and an integral multiple of the horizontal synchronization frequency, the color subcarrier frequency can be easily extracted. Therefore, even in the direct encoding method, digital color demodulation becomes easy in terms of hardware.

In addition, in order to reproduce the color subcarrier frequency using the sampling theorem, the burst signal passes through the color subcarrier signal regeneration circuit, and the color subcarrier frequency obtained from this and the digital image that does not pass through the color subcarrier signal regeneration circuit are Although a lag occurs between the signals, these signals are once stored in memory and synchronized, so the time lag is corrected.

In this way, according to the present circuit, it is possible to select the sampling frequency for A/D conversion to be an arbitrary multiple of the color subcarrier frequency, not limited to an integral multiple.

[Example code] Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a block diagram showing an embodiment of a video signal processing circuit of the present invention.

The analog video signal A is separated into a horizontal synchronization signal B by a synchronization signal separation circuit 11 . And PLL circuit 1
2, a horizontal synchronizing signal B, and a horizontal synchronizing signal C obtained by dividing the sampling clock D in a frequency dividing circuit 3.
A sampling clock D synchronized with the horizontal synchronization signal B is generated. In order to satisfy the sampling theorem, this sampling clock D must have a frequency that is at least twice the bandwidth W of the luminance signal and an integral multiple of the horizontal synchronization frequency FH.

The A/D conversion circuit 13 performs A/D conversion on the video signal A using the sampling clock D, and outputs a digital video signal E. Here, one line of valid video area data shown in FIG. 5 of the video signal E is written into the video data line memory 14. At the same time, the burst signal region data shown in FIG. 5 is input to the color subcarrier signal reproducing circuit 15, data at two arbitrary consecutive points is extracted using the sampling clock D, and the color subcarrier signal G is converted into a digital signal using the sampling theorem. The data is reproduced as a chrominance subcarrier line memory 16 and written to the color subcarrier line memory 16 at a predetermined timing.

Next, video data F is read out from the video data line memory 14, and color subcarrier data H is read out from the color subcarrier line memory 16, respectively. The video data F is digitally Y/C separated by the digital comb filter 1B and separated into luminance signal data and color signal data J. The color signal data J is processed in the color signal demodulation circuit 19.
The color subcarrier data H is calculated as a reference, and the color difference signal L (
1 or B-Y), color difference signal M (Q or R-Y)
) is color demodulated.

FIG. 4 shows an example of the configuration of the color subcarrier signal reproducing circuit 15, which is the core of this embodiment.

In the latches 41 and 42, arbitrary two consecutive points of data O and P are extracted from the burst signal region data of the digital video signal data E using the sampling clock D. Then, the ROM 44 calculates the equation (1) shown below to obtain the phase difference Q. Also, from the output R of the counter 43 for the number of pixels in one line synchronized with the phase difference Q and the sampling clock D, in the ROM 45Cm (2)
The equation is calculated and color subcarrier data G is sent out.

The two arithmetic ROMs 44 and 45 described above can be easily realized using digital technology and can be constructed at low cost compared to A/D conversion circuits and PLL circuits that require precision.

Note that equations (1) and (2) are derived from the known sampling theorem.

Q=s i n-'(DI/CC) SA= S i n(2-π* fso/F8CA=c
os (2 π11f So/FS where D] S SC G”CCX5 1st sample data 2nd sample data Sampling frequency Color subcarrier frequency n (Q+R (2◆π・f sc/F 5)) where ,
R: Counter output, 0 to (number of pixels in one line) As described above, according to this embodiment, in the video signal processing circuit, an A/D conversion circuit that converts an analog video signal from analog to digital, and an analog From the video signal to the horizontal synchronization signal F), I
A synchronization signal separation circuit that separates the horizontal synchronization signal FH and the sampling clock FS, a PLL circuit that synchronizes the horizontal synchronization signal FH and the sampling clock FS,
A color subcarrier signal reproducing circuit that reproduces a frequency color subcarrier signal from a D/D-converted burst signal based on the sampling theorem, a line memory that stores one line of video data, and a color subcarrier signal that reproduces the reproduced digital color subcarrier signal. Line memory for storing data and Y/C for digitally separating Y/C.
It is equipped with a C separation circuit, a color signal demodulation circuit that digitally demodulates the C signal, and a timing generation circuit that creates the timing for writing each data into the line memory for the video signal and the line memory for the color subcarrier signal. be.

Therefore, regardless of whether the sampling frequency is an integer multiple of the color subcarrier frequency, the sampling theorem allows the color subcarrier frequency to be easily reproduced from the original video signal, which eliminates the need for an expensive and complicated PLL circuit. Unlike conventional circuits that require an additional A/D conversion circuit, the circuit does not become expensive or complicated.

Furthermore, since it uses a direct encoding method, Y/C separation and color demodulation are digitally processed.
The number of adjustment points can be reduced, reducing adjustment man-hours.
Changes over time can also be eliminated. Therefore, the image quality is not significantly affected by the performance of the analog comb filter, as is the case with conventional circuits that use the separate encoding method, and since the analog circuit is large, there are many adjustment points. There is no need to store it away or cause significant changes over time.

In the above embodiment, the memory for storing video data and color subcarrier data was described as a line memory.
The present invention is not limited to this. In short, any memory that temporarily stores data in order to eliminate the time delay when passing through the color subcarrier signal reproducing circuit may be used; for example, a field memory or the like may be used.

[Effects of the Invention] As explained in detail above, according to the present invention, after the video signal is A/D converted, the data of the color subcarrier is digitally reproduced from the data of the burst signal part using the sampling theorem. Therefore, if the sampling frequency during A/D conversion is more than twice the bandwidth of the luminance signal and an integral multiple of the horizontal synchronization frequency, digital color demodulation is possible even if it is not an integral multiple of the color subcarrier frequency. can be easily done.

Furthermore, since Y/C separation and color demodulation are processed digitally, excellent image quality can be obtained without any adjustment.

[Brief explanation of the drawing]

Figure 1 is a block diagram of a video signal processing circuit according to an embodiment of the present invention, Figure 2 is a block diagram of conventional color demodulation and A/D conversion in direct encoding, and Figure 3 is a block diagram of conventional color demodulation and A/D conversion in separate encoding. FIG. 4 is a block diagram of demodulation and A/D conversion, FIG. 4 is a configuration diagram of a color subcarrier signal reproducing circuit according to this embodiment, and FIG. 5 is an explanatory diagram of a video signal. 11 is a synchronization signal separation circuit, 12 is a PLL circuit, and 13 is A
14 is a video data line memory that stores one line of video data; 15 is a color subcarrier signal reproducing circuit; 16 is a color subcarrier line memory that stores the reproduced digital color subcarrier signal; 17 is a color subcarrier line memory that stores the reproduced digital color subcarrier signal; Timing generation circuit, 18 is a digital comb filter on the Y/C9 separate circuit, 19 is a color signal demodulation circuit, A is an analog video signal, B is a horizontal synchronization signal, D is a sampling clock, E is a digital video signal, G is the color subcarrier signal.

Claims (1)

[Claims] In a video signal processing circuit that directly A/D converts an analog video signal, separates Y/C using a digital filter, and demodulates a color difference signal from the separated C signal, a color subcarrier signal reproducing circuit that reproduces a color subcarrier signal from the reproduced burst signal based on the sampling theorem; a video data memory that stores video data from the A/D converted video signal; and a color subcarrier signal reproducing circuit that reproduces the color subcarrier signal from the reproduced color subcarrier signal. a color subcarrier memory for storing subcarrier data; and synchronization of the video data stored in the video data memory and the color subcarrier data stored in the color subcarrier memory via the color subcarrier signal reproducing circuit. and a timing generation circuit which takes the color subcarrier data stored in the color subcarrier memory as a reference, and demodulates the color difference signal from the C signal obtained by separating it with a digital filter. video signal processing circuit.