JP3606592B2 - Digital video signal transmission device - Google Patents

Description

[0001]
[Industrial application fields]
The present invention relates to a digital video signal transmission apparatus for converting a standard video signal having a high resolution (for example, a high-definition signal) into a standard video signal having a lower resolution (for example, the NTSC system).
[0002]
[Prior art]
Systems with higher resolution than existing television systems such as the NTSC system (525 lines / 60 fields) and the PAL system (625/50) have been proposed. For example, the 1125/60 system (also referred to as a high-vision system) and the 1250/50 system (also referred to as an HD-MAC system) are typical high-resolution television systems. When transmitting this high-resolution video signal (hereinafter referred to as HD signal), so-called down-conversion may be performed in which the video signal is converted into a video signal similar to an existing standard-definition method.
[0003]
If the transmission band of the digital VTR is insufficient for recording / reproduction of HD signals, down-conversion is necessary when a high-resolution video signal is to be reproduced by an existing monitor. For down-conversion, a sub-sampling technique that thins out pixels of the HD signal is used. In addition, it is necessary to convert the number of lines.
[0005]
[Problems to be solved by the invention]
As one of the systems for down-conversion, one pixel of a standard resolution signal (hereinafter referred to as an STD signal) is created from several pixels of an HD signal, and an image of the HD signal is subsampled and processed. Can be considered. Also, the number of lines needs to be converted during down-conversion. For example, when the number of lines is halved for each field, there is a problem that a difference in resolution occurs between fields in the converted STD signal image.
[0007]
Therefore, purpose of this invention, when converting the number of lines, is to provide a transmission apparatus in a digital video signal that the difference in resolution occurs is prevented between fields.
[0008]
[Means for Solving the Problems]
The invention of claim 1 provides a transmission apparatus to which a second standard video signal having a resolution higher than that of the first standard video signal is supplied.
Subsampling means for subsampling the second standard video signal and halving the number of pixels in the horizontal direction;
Processing means for performing image processing on the subsampled second standard video signal and outputting a signal of only one of the four pixels of the adjacent second standard video signal to the transmission means;
Converting means for forming a digital video signal having a resolution of the first standard video signal from the subsampled second standard video signal and outputting the digital video signal to the transmission means;
The conversion means multiplies the values of two pixels not thinned out by the sub-sampling means among the four pixels of the adjacent second standard video signal by the first and second weighting factors, respectively. The added value is generated as the pixel value of the first standard video signal corresponding to the four pixels,
The processing means is a digital video signal transmission apparatus that outputs only a pixel signal multiplied by a smaller weight coefficient among the first and second weight coefficients to the transmission means .
[0010]
During down-conversion, when half the number of line, it is possible to a spatial distance between the lines is constant, also natural, equally the resolution between fields.
[0011]
【Example】
Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 shows the entire system of one embodiment. An input image (digital HD signal) is supplied to the sub-sampling circuit 1. The sub-sampling circuit 1 halves the number of pixels of the HD signal.
[0012]
An HD image processing circuit 2 and an HD-STD conversion circuit 3 are connected after the sub-sampling circuit 1. Outputs of the image processing circuit 2 and the conversion circuit 3 are transmitted via the transmission path 4. On the receiving side, an inverse conversion circuit 5 is provided, and an HD output image and an STD output image are taken out as outputs thereof. Specifically, the transmission path 4 is a wireless transmission, magnetic recording / reproduction process, or the like.
[0013]
With reference to FIG. 2, subsampling and down-conversion processing will be described. A, B, C, and D indicate four adjacent pixels in the HD image. In the sub-sampling circuit 1, 2 pixels A and B surrounded by circles among these 4 pixels are transmission pixels, and 2 pixels C and D surrounded by triangles are non-transmission pixels (thinned pixels). Then, the data value of the pixel a corresponding to the STD signal is obtained from the data after sub-sampling, that is, the data of the pixels A and B by the following equation.
[0014]
a = α1 ・ A + α2 ・ B
α1 and α2 are weighting factors.
[0015]
In the inverse conversion circuit 5 on the receiving side, B ^ can be calculated from the received data a ^ and A ^. However, although a distortion component due to quantization appears, the number of transmission bits can be considerably reduced, so that the quantization step width can be reduced. As a result, the amount of distortion in B ^ can be reduced.
[0016]
Further, in the case of (α1> α2), B multiplied by a smaller coefficient α2 may be transmitted as an HD signal. When calculating A ^ on the receiving side,
A ^ = (1 / α1) · (a ^ −α2B ^)
It becomes. As can be seen from this equation, when the same amount of quantization distortion occurs in a ^ and B ^, the influence of quantization distortion on A ^ is greater than when A ^ is transmitted and B ^ is obtained by calculation. Can be reduced.
[0017]
The conversion circuit 3 also performs a process of halving the number of lines. FIG. 3 illustrates the conventional line number conversion. FLD1 and FLD2 represent the first field and the second field constituting one frame, and each dot represents a spatial position of each line. The upper and lower two lines of the HD image are set as one set, and the average value of the pixels of each line is one line of the STD image. In this way, in the STD image, the line spacing does not become constant (2d) between the first field and the second field, and becomes d and 3d as shown in FIG.
[0018]
As one method for preventing such a phase shift, as shown in FIG. 4, the first field FLD1 uses a 3-tap filter that receives data of three adjacent lines, and the second field FLD2 Conversion of the number of lines using a 2-tap filter that receives two lines of data as input is considered. However, in this method, as a result of the difference in the number of taps of the filter, there arises a problem that the resolution is different between the first field FLD1 and the second field FLD2 in the STD image.
[0019]
The present invention prevents the above-described phase shift and the difference in resolution between fields as a result of line number conversion. 5 and 6 are examples of a line number conversion circuit to which the present invention is applied. FIG. 5 shows the configuration when processing the first field, and FIG. 6 shows the configuration when processing the second field.
[0020]
5 and 6, H indicates a line delay circuit. Two line delay circuits are connected in series, and the HD signal of the first field or the second field is supplied to one end thereof. From the taps derived from the series connection of the line delay circuits (referred to as the first tap, the second tap, and the third tap in order from the input side), three pixel data of three lines that are temporally continuous are extracted.
[0021]
Each pixel data is supplied to a coefficient multiplier and multiplied by coefficients w1, w2 and w3. Output signals of these multipliers are supplied to the adder circuit 12. The output signal of the adder circuit 12 is supplied to the subsampling circuit 13. The sub-sampling circuit 13 separates necessary data. An output signal of the first field or the second field of the STD image is generated at the output terminal 14. Here, the filter coefficient is asymmetric (that is, w1 ≠ w3). As an example, (w1 = 1/8, w2 = 1/2, w3 = 3/8.
[0022]
When the first field shown in FIG. 5 is processed, the data of the first tap is multiplied by w1, the data of the second tap is multiplied by w2, and the data of the third tap is multiplied by w3. It is done. As shown in FIG. 6, in the second field, the coefficients for the first tap and the third tap are interchanged.
[0023]
As a result of the above-described processing, as shown in FIG. 7, in the STD image, there is no line phase shift between fields. However, since the number of filter taps used is the same between the two fields, it is possible to prevent the resolution from being different between the fields.
[0024]
Further, when a filter is used, there is a problem that blur and ringing occur after conversion. From this point, it is preferable not to use a filter. As shown in FIG. 8, the HD signal in the first field is guided to the output terminal 14 simply by passing through the sub-sampling circuit 13. Although not shown, for the second field, a 2-tap filter to which data is respectively supplied from two adjacent lines is used.
[0025]
In this way, as shown in FIG. 9, with respect to the first field, lines that are not thinned out of the two lines are directly output. For the second field, the average value of two lines is output. Accordingly, line phase shift can be prevented, and no filter processing is performed in the first field, thereby preventing image blurring and ringing.
[0026]
Regarding the above-mentioned line number conversion, as shown in FIG. 1, it is not necessary to use the subsampled HD signal, and all data of the HD image before the subsampled may be used.
[0027]
【The invention's effect】
Line number conversion of this invention not only can prevent the phase shift of lines between fields, that resolution is different between the fields can be prevented. Furthermore, since data is directly used in one field in line number conversion, image deterioration due to filtering can be prevented.
[Brief description of the drawings]
FIG. 1 is a block diagram showing an outline of a system according to an embodiment of the present invention.
FIG. 2 is a schematic diagram for explaining subsampling according to an embodiment of the present invention;
FIG. 3 is a schematic diagram of an example of conventional line number conversion.
FIG. 4 is a schematic diagram of another example of conventional line number conversion.
FIG. 5 is a block diagram of a configuration relating to a first field of an example of a line number conversion circuit according to the present invention;
FIG. 6 is a block diagram of a configuration relating to a second field of another example of the line number conversion circuit according to the present invention;
FIG. 7 is a schematic diagram showing an operation of an example of a line number conversion circuit according to the present invention.
FIG. 8 is a schematic diagram showing a configuration relating to a first field of another example of the line number conversion circuit according to the present invention;
FIG. 9 is a schematic diagram showing the operation of another example of the line number conversion circuit according to the present invention.
[Explanation of symbols]
1 Sub-sampling circuit 3 HD-STD conversion circuit

Claims (2)

In a transmission apparatus to which a second standard video signal having a resolution higher than that of the first standard video signal is supplied,
Subsampling means for subsampling the second standard video signal and halving the number of pixels in the horizontal direction;
Processing means for performing image processing on the subsampled second standard video signal and outputting a signal of only one of the four pixels of the adjacent second standard video signal to the transmission means When,
Conversion means for forming a digital video signal having the resolution of the first standard video signal from the subsampled second standard video signal and outputting the digital video signal to the transmission means;
The converting means includes first and second weighting factors for the values of two pixels not skipped by the sub-sampling means among the four pixels of the adjacent second standard video signal. A value obtained by multiplying and adding is generated as a pixel value of the first standard video signal corresponding to the four pixels,
The digital video signal transmission apparatus, wherein the processing means outputs only a pixel signal multiplied by a smaller weighting coefficient to the transmission means among the first and second weighting coefficients . 2. The digital video signal transmission apparatus according to claim 1, wherein the transmission means is configured to transmit a predetermined output wirelessly.

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