CN102547309A - Detection calculating method and device for frequency shift of composite video broadcast signal (CVBS) - Google Patents

Abstract

The invention provides a method for detecting and calculating the frequency offset of a CVBS signal, which includes the following steps: S1, collecting several CVBS signals with known frequency offsets; S2, calculating the corresponding correlation factor of each CVBS signal; S3, obtaining the correlation The relationship between the factor and the frequency offset, the relationship is a table or an analytical expression; S4, for the unknown CVBS signal of the newly input frequency offset, calculate its correlation factor, according to the relationship between the correlation factor and the frequency offset obtained in step S3 , calculate its frequency offset. The detection and calculation method and device of the CVBS signal frequency offset of the present invention do not need an external reference frequency, but only use the relationship between the lines inside the signal to derive its frequency offset, so as to obtain the correct or better frequency offset through correction. quality images.

Description

Method and device for detecting and calculating CVBS signal frequency offset

technical field

The invention relates to the technical field of image processing, in particular to a method and device for detecting and calculating a CVBS signal frequency offset.

Background technique

CVBS (Composite Video Broadcast Signal or Composite Video Blanking and Sync) is a composite video broadcast signal or composite video blanking and synchronization. It is an analog TV program (picture) signal before it is combined with a sound signal and modulated to a radio frequency carrier. Format. CVBS is a widely used standard, also known as baseband video or RCA video, which is the traditional image data transmission method of (USA) National Television Standards Committee (NTSC) TV signal, which transmits data in analog waveform. Composite video contains color difference (hue and saturation) and luminance (brightness) information and synchronizes them in pedestal pulses and transmits them on the same signal.

The calculation formula of the CVBS signal is CVBS=Luma+Chroma, where Luma is the brightness carrier and Chroma is the color carrier. The calculation formula of the color carrier Chroma is Chroma=u*sin(2πft)+v*cos(2πft), where f is the frequency of the color carrier. The color carrier frequency of standard PAL TV is 4.43361875MHz, and the color carrier frequency of standard NTSC TV is 3.579545MHz. But in actual situations, this frequency will be shifted, and the frequency shift basically occurs at the transmitting end of the image signal. Or for non-standard signals, the frequency will also have an offset. In order to correct the CVBS signal, the magnitude of the frequency offset must be known, but the magnitude of the frequency offset cannot be detected in the prior art.

In view of this, it is necessary to propose a method and device for detecting and calculating the frequency offset of a CVBS signal.

Contents of the invention

The object of the present invention is to provide a method and device for detecting and calculating the frequency offset of a CVBS signal.

A kind of detection calculation method of CVBS signal frequency offset of the present invention, described method comprises the following steps:

S1. Collect several CVBS signals with known frequency offsets;

S2. Calculating a corresponding correlation factor for each CVBS signal;

S3. Obtain the relationship between the correlation factor and the frequency offset, where the relationship is a table or an analytical expression;

S4. For the newly input CVBS signal whose frequency offset is unknown, calculate its correlation factor, and calculate and obtain its frequency offset according to the relationship between the correlation factor and frequency offset obtained in step S3.

As a further improvement of the present invention, the step S2 is specifically:

S211. Take the CVBS image composite signal set at the burst of the previous row;

S212. Get the CVBS image composite signal set at the burst of the current row;

S213. Perform Hilbert filtering on the signal points obtained in step S212;

S214. Multiply the result of step S213 and each signal point corresponding to the signal point set in step S211;

S215. Sum the results of step S214.

As a further improvement of the present invention, the step S2 is specifically:

S221. Get the CVBS image composite signal set at the burst of the current line;

S222. Take the CVBS image composite signal set at the burst of the next row;

S223. Perform Hilbert filtering on the signal points obtained in step S222;

S224. Multiply the result of step S223 and each signal point corresponding to the signal point set in step S221;

S225. Sum the results of step S224.

As a further improvement of the present invention, the correlation factor correlation_factor is passed $\mathrm{correlation}\_\mathrm{factor}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}\mathrm{top}\_\mathrm{line}\_\mathrm{burst}\left(i\right)*\mathrm{Hilbert\; Filtering}(\mathrm{cur}\_\mathrm{line}\_\mathrm{burst}\left(i\right))$ Calculated, i is the coordinate of the sampling point, M is the number of sampling points of the burst, and HilbertFiltering refers to Hilbert filtering.

As a further improvement of the present invention, the step S4 includes:

S411, with the correlation factor as x and the frequency offset as y, a table (x[i], y[i]) is obtained, where i is the number of CVBS signals with known frequency offset;

S412. Solve the corresponding frequency offset according to the table in step S411.

As a further improvement of the present invention, the step S4 includes:

S421. Using the correlation factor as x and the frequency offset as y, fit a continuous straight line or curve to obtain analytical expressions for x and y;

S422. Calculate the corresponding frequency offset by using the analytical expression in step S421.

As a further improvement of the present invention, the analytical expressions of x and y are a linear functional relationship or a quadratic functional relationship or a higher functional relationship of y with respect to x.

As a further improvement of the present invention, the step S4 also includes:

For a new input CVBS signal whose frequency offset is unknown, the correlation factor x is calculated;

The correlation factor x falls between x[i] and x[i+1], look up the table to get the frequency offsets y[i] and y[i corresponding to the correlation factors x[i] and x[i+1] +1] the size of;

求出相关因子x对应的频率偏移y的大小。According to the formula

Calculate the magnitude of the frequency offset y corresponding to the correlation factor x.

As a further improvement of the present invention, the step S4 also includes:

For a new input CVBS signal whose frequency offset is unknown, the correlation factor x is calculated;

Substitute the correlation factor x into the analytical expressions of x and y obtained from the solution, and obtain the magnitude of the frequency offset y corresponding to the correlation factor x.

Correspondingly, a detection calculation device of a CVBS signal frequency offset, the device includes:

A unit for acquiring several CVBS signals at known frequency offsets;

A unit for calculating a corresponding correlation factor for each CVBS signal;

A unit for obtaining a relationship between a correlation factor and a frequency offset, the relationship being a table or an analytical expression;

A unit for calculating the correlation factor of the newly input CVBS signal whose frequency offset is unknown, and calculating the frequency offset according to the relationship between the correlation factor and the frequency offset obtained in step S3.

The beneficial effects of the present invention are: the present invention does not need an external reference frequency, but only uses the relationship between lines within the signal to derive its frequency offset, thereby obtaining correct or better quality images through correction.

Description of drawings

FIG. 1 is a flowchart of a method for detecting a frequency offset of a CVBS signal in an embodiment of the present invention.

Fig. 2 is a schematic diagram of a CVBS waveform signal in the present invention.

Fig. 3 is a schematic diagram of the phase relationship between the current line and the previous line in the case of no frequency offset in the present invention.

Fig. 4 is a schematic diagram of the phase relationship between the current line and the previous line in the case of frequency offset in the present invention.

Fig. 5 is a schematic diagram of the relationship between the correlation factor and the frequency offset in the present invention.

FIG. 6 is a flow chart of correlation factor calculation in an embodiment of a method for detecting a frequency offset of a CVBS signal according to the present invention.

FIG. 7 is a flow chart of correlation factor calculation in another embodiment of the detection method of CVBS signal frequency offset according to the present invention.

FIG. 8 is a flow chart of frequency offset calculation in an embodiment of a method for detecting a frequency offset of a CVBS signal according to the present invention.

FIG. 9 is a flow chart of frequency offset calculation in another embodiment of the method for detecting a frequency offset of a CVBS signal according to the present invention.

Detailed ways

The present invention will be described in detail below in conjunction with various embodiments shown in the drawings. However, these embodiments do not limit the present invention, and any structural, method, or functional changes made by those skilled in the art according to these embodiments are included in the protection scope of the present invention.

Referring to Fig. 1, it is a flowchart of a method for detecting and calculating CVBS signal frequency offset in an embodiment of the present invention, the method for detecting includes the following steps

S1. Collect several CVBS signals with known frequency offsets. Referring to Figure 2, it is a CVBS signal waveform. Preferably, the frequency offset of the key frequency offset point of the CVBS signal can be selected from [-2000, +2000] Hz, and the step size is 100 Hz or less;

大小，从而将频率f的信息转化为相位

的信息。图3中在没有频率偏移的情况下，相关因子为0，图4中在有频率偏移的情况下，相关因子不为0，相关因子随着频率偏移的改变而改变，如果频率是正的偏移，则相关因子为正；如果频率是负的偏移，则相关因子为负，相关因子的正负不但和频率偏移的正负有关，而且，可以从相关因子的大小推断出频率偏移的大小；S2. Calculate the correlation factor corresponding to each CVBS signal. Refer to Figure 3 and Figure 4, which show the phase relationship between the current line and the previous line without frequency offset and frequency offset respectively. In the case of no offset, the phases of the current line and the previous line are just opposite, and also That is, the phase difference is 180 degrees, and in the case of a frequency offset, the phase of the current row and the previous row is not 180 degrees, and an offset has occurred. Where the CVBS signal is in its burst, it has the information of frequency f, and the frequency f of each CVBS signal in its burst is obtained, according to the formula The phase corresponding to each frequency f can be calculated

size, thus converting the information of the frequency f into the phase

Information. In the case of no frequency offset in Figure 3, the correlation factor is 0, and in the case of frequency offset in Figure 4, the correlation factor is not 0, and the correlation factor changes with the frequency offset. If the frequency is positive The correlation factor is positive; if the frequency is a negative offset, the correlation factor is negative. The positive or negative of the correlation factor is not only related to the positive or negative of the frequency offset, but also the frequency can be deduced from the magnitude of the correlation factor the size of the offset;

S3. Obtain the relationship between the correlation factor and the frequency offset, where the relationship is a table or an analytical expression. According to the calculation, a relationship chart of correlation factors and frequency offsets similar to that shown in Figure 5 is obtained. Each key frequency offset point corresponds to a key correlation factor, and each key correlation factor also corresponds to a key frequency offset. The obtained The relationship between the correlation factor and the frequency offset can be a table or a straight line or a curve, etc.;

S4. For the newly input CVBS signal whose frequency offset is unknown, calculate its correlation factor, and calculate and obtain its frequency offset according to the relationship between the correlation factor and frequency offset obtained in step S3.

In step S2, the correlation factor correlation_factor can be obtained by the formula $\mathrm{correlation}\_\mathrm{factor}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}\mathrm{top}\_\mathrm{line}\_\mathrm{burst}\left(i\right)*\mathrm{Hilbert\; Filtering}(\mathrm{cur}\_\mathrm{line}\_\mathrm{burst}\left(i\right))$ Calculated, where i is the coordinate of the sampling point, M is the number of sampling points of the burst, and HilbertFiltering refers to performing Hilbert filtering. The sampling coordinates can be the current line and the previous line, or the current line and the next line.

As shown in Figure 6, when the sampling coordinates are the current row and the previous row, the calculation steps of the correlation factor correlation_factor are as follows:

S211, the CVBS image composite signal set (1, 2, ... M) at the burst of the previous line;

S212. Get the CVBS image composite signal set (1, 2, ... M) at the burst of the current row;

S213. Perform Hilbert filtering on the signal points obtained in step S212, wherein the meaning of "Hilbert filtering" refers to turning the phase of the signal to 90 degrees;

S214. Multiply the result of step S213 and each signal point corresponding to the signal point set in step S211;

S215. Sum the results of step S214.

When the sampling coordinates are the current row and the next row, the calculation steps of the correlation factor correlation_factor are as follows:

S221. Get the CVBS image composite signal set (1, 2, ... M) at the burst of the current line;

S222. Take the CVBS image composite signal set (1, 2, ... M) at the burst of the next row;

S223, performing Hilbert filtering on the signal points taken in step S222, the meaning of "Hilbert filtering" refers to turning the phase of the signal to 90 degrees;

S224. Multiply the result of step S223 and each signal point corresponding to the signal point set in step S221;

S225. Sum the results of step S224.

In the above steps S214 and S224, if the result of the multiplication is 0, it means that there is no offset, and if the result of the multiplication is not 0, it means that there is an offset.

In step S4, the calculated key point frequency offset can be obtained by two methods of curve fitting or interpolation.

As shown in Figure 8, the method of interpolation includes the following steps:

S411, with the correlation factor as x and the frequency offset as y, a table (x[i], y[i]) is obtained, where i is the number of CVBS signals with known frequency offset;

S412. Solve the corresponding frequency offset according to the table in step S411.

The steps to calculate the frequency offset of an unknown CVBS signal are:

For a new input CVBS signal whose frequency offset is unknown, the correlation factor x is calculated;

The correlation factor x falls between x[i] and x[i+1], look up the table to get the frequency offsets y[i] and y[i corresponding to the correlation factors x[i] and x[i+1] +1] the size of;

求出相关因子x对应的频率偏移y的大小。According to the formula

Calculate the magnitude of the frequency offset y corresponding to the correlation factor x.

As shown in Figure 9, the method of curve fitting comprises the following steps:

S421. With the correlation factor as x and the frequency offset as y, fit a continuous straight line or curve to obtain an analytical expression about x and y, such as y=a*x+b (straight line) or y=c* x*x+d*x+f (quadratic curve) or higher degree curve;

S422. Calculate the corresponding frequency offset by using the analytical expression in step S421. If the analytical expression to be obtained is y=a*x+b, where a=5.2309 and b=-18.499, then the size of the corresponding frequency offset y can be obtained through the correlation factor x.

The steps to calculate the frequency offset of an unknown CVBS signal are:

For a new input CVBS signal whose frequency offset is unknown, the correlation factor x is calculated;

Substitute the correlation factor x into the analytical expressions of x and y obtained from the solution, and obtain the magnitude of the frequency offset y corresponding to the correlation factor x.

The detection calculation device of CVBS signal frequency offset in one embodiment of the present invention, this device comprises:

Unit for acquiring several CVBS signals at known frequency offsets. Referring to Figure 2, it is a CVBS signal waveform. Preferably, the frequency offset of the key frequency offset point of the CVBS signal can be selected from [-2000, +2000] Hz, and the step size is 100 Hz or less;

大小，从而将频率f的信息转化为相位

的信息。图3中在没有频率偏移的情况下，相关因子为0，图4中在有频率偏移的情况下，相关因子不为0，相关因子随着频率偏移的改变而改变，如果频率是正的偏移，则相关因子为正；如果频率是负的偏移，则相关因子为负，相关因子的正负不但和频率偏移的正负有关，而且，可以从相关因子的大小推断出频率偏移的大小；Unit for calculating the corresponding correlation factor for each CVBS signal. Refer to Figure 3 and Figure 4, which show the phase relationship between the current line and the previous line without frequency offset and frequency offset respectively. In the case of no offset, the phases of the current line and the previous line are just opposite, and also That is, the phase difference is 180 degrees, and in the case of a frequency offset, the phase of the current line and the previous line is not 180 degrees, and an offset occurs. Where the CVBS signal is in its burst, it has the information of frequency f, and the frequency f of each CVBS signal in its burst is obtained, and the phase corresponding to each frequency f can be calculated according to the formula

size, thus converting the information of the frequency f into the phase

Information. In the case of no frequency offset in Figure 3, the correlation factor is 0, and in the case of frequency offset in Figure 4, the correlation factor is not 0, and the correlation factor changes with the frequency offset. If the frequency is positive The correlation factor is positive; if the frequency is a negative offset, the correlation factor is negative. The positive or negative of the correlation factor is not only related to the positive or negative of the frequency offset, but also the frequency can be deduced from the magnitude of the correlation factor the size of the offset;

A unit for obtaining a relationship between correlation factors and frequency offsets, said relationship being a table or an analytical expression. According to the calculation, a relationship chart of correlation factors and frequency offsets similar to that shown in Figure 5 is obtained. Each key frequency offset point corresponds to a key correlation factor, and each key correlation factor also corresponds to a key frequency offset. The obtained The relationship between the correlation factor and the frequency offset can be a table or a straight line or a curve, etc.;

A unit for calculating the correlation factor of the newly input CVBS signal whose frequency offset is unknown, and calculating the frequency offset according to the relationship between the correlation factor and the frequency offset obtained in step S3.

In summary, the method and device for detecting and calculating the frequency offset of a CVBS signal in the present invention does not require an external reference frequency, but only uses the relationship between lines within the signal to derive its frequency offset, thereby obtaining Correct or better quality images.

It should be understood that although this description is described according to implementation modes, not each implementation mode only contains an independent technical solution, and this description in the description is only for clarity, and those skilled in the art should take the description as a whole, and each The technical solutions in the embodiments can also be properly combined to form other embodiments that can be understood by those skilled in the art.

The series of detailed descriptions listed above are only specific descriptions for feasible implementations of the present invention, and they are not intended to limit the protection scope of the present invention. Any equivalent implementation or implementation that does not depart from the technical spirit of the present invention All changes should be included within the protection scope of the present invention.

Claims (10)

1. a detection calculation method of CVBS signal frequency deviation, is characterized in that, described method comprises the following steps: S1. Collect several CVBS signals with known frequency offsets; S2. Calculating a corresponding correlation factor for each CVBS signal; S3. Obtain the relationship between the correlation factor and the frequency offset, where the relationship is a table or an analytical expression; S4. For the newly input CVBS signal whose frequency offset is unknown, calculate its correlation factor, and calculate and obtain its frequency offset according to the relationship between the correlation factor and frequency offset obtained in step S3. 2. The method according to claim 1, wherein the step S2 is specifically: S211. Take the CVBS image composite signal set at the burst of the previous row; S212. Get the CVBS image composite signal set at the burst of the current line; S213. Perform Hilbert filtering on the signal points obtained in step S212; S214. Multiply the result of step S213 and each signal point corresponding to the signal point set in step S211; S215. Sum the results of step S214. 3. The method according to claim 1, wherein the step S2 is specifically: S221. Get the CVBS image composite signal set at the burst of the current line; S222. Take the CVBS image composite signal set at the burst of the next row; S223. Perform Hilbert filtering on the signal points obtained in step S222; S224. Multiply the result of step S223 and each signal point corresponding to the signal point set in step S221; S225. Sum the results of step S224. 4. according to the method described in claim 2 or 3, it is characterized in that, described correlation factor correlation_factor passes $\mathrm{correlation}\_\mathrm{factor}=\underset{i=1}{\overset{m}{\mathrm{\Σ}}}\mathrm{top}\_\mathrm{line}\_\mathrm{burst}\left(i\right)*\mathrm{Hilbert\; Filtering}(\mathrm{cur}\_\mathrm{line}\_\mathrm{burst}\left(i\right))$ Calculated, i is the coordinate of the sampling point, M is the number of sampling points of the burst, and HilbertFiltering refers to Hilbert filtering. 5. The method according to claim 1, wherein said step S4 comprises: S411, with the correlation factor as x and the frequency offset as y, a table (x[i], y[i]) is obtained, where i is the number of CVBS signals with known frequency offset; S412. Solve the corresponding frequency offset according to the table in step S411. 6. The method according to claim 1, wherein said step S4 comprises: S421. Using the correlation factor as x and the frequency offset as y, fit a continuous straight line or curve to obtain analytical expressions for x and y; S422. Calculate the corresponding frequency offset by using the analytical expression in step S421. 7. The method according to claim 6, wherein the analytical expressions of x and y are a linear functional relationship or a quadratic functional relationship or a higher-order functional relationship of y with respect to x. 8. The method according to claim 5, wherein the step S4 further comprises: For a new input CVBS signal whose frequency offset is unknown, the correlation factor x is calculated; The correlation factor x falls between x[i] and x[i+1], look up the table to get the frequency offsets y[i] and y[i corresponding to the correlation factors x[i] and x[i+1] +1] the size of; According to the formula

Calculate the magnitude of the frequency offset y corresponding to the correlation factor x. 9. The method according to claim 7, wherein the step S4 further comprises: For a new input CVBS signal whose frequency offset is unknown, the correlation factor x is calculated; Substitute the correlation factor x into the analytical expressions of x and y obtained from the solution, and obtain the magnitude of the frequency offset y corresponding to the correlation factor x. 10. a kind of detection computing device of CVBS signal frequency offset according to claim 1, is characterized in that, described device comprises: A unit for acquiring several CVBS signals at known frequency offsets; A unit for calculating a corresponding correlation factor for each CVBS signal; A unit for obtaining a relationship between a correlation factor and a frequency offset, the relationship being a table or an analytical expression; A unit for calculating the correlation factor of the newly input CVBS signal whose frequency offset is unknown, and calculating the frequency offset according to the relationship between the correlation factor and the frequency offset obtained in step S3.

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