JPH11205089A - Digital video recording apparatus - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a digital video recording apparatus with which an optimum recording characteristic is obtained at autimes, even in connection with the video data supply source of an arbitrary characteristic. SOLUTION: This apparatus is provided with a digital filter 1 having plural switchable high-band attenuating characteristic and a high-band emphasizing characteristics, a sampling rate converting circuit 2 for converting the sampling frequency of output data of the digital filter 1, a data change over switch 3 for inputting output data of the digital filter 1 and output data of the sampling rate conversion circuit 2 and selectively outputting one of them and a compression recording part 4 for compressing output data of the data change over switch 3 and recording it. A proper high-band attenuating characteristic is set in the digital filter 1, in accordance with the characteristic of the video supply source such as video camera, so that the overall frequency characteristic of the video data supply source, the digital filter 1 and the sampling rate conversion circuit 2 is made have characteristics which are optimum for a compression format, even in the use with any kind of video data supply source.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a digital video recording device such as a digital video tape recorder.

[0002]

2. Description of the Related Art In recent years, with the development of magnetic recording / reproducing technology and high-efficiency compression technology of image data, video tape recorders have been digitized. As a standard for digital video tape recorders mainly for consumer use, HDD
Specification of Consu by IGITAL VCR CONFERENCE
mer-Use Digital VCRs Using 6.3mm Magnetic Tape
(Hereinafter abbreviated as “DV format”). In the DV format, a conventional NTSC video signal is treated as a 4: 1: 1 digital video data format, and a PAL video signal is treated as a 4: 2: 0 digital video data format, and compression recording, reproduction and expansion are performed. A normal density mode (hereinafter abbreviated as “SD mode”) is defined. Furthermore, in the DV format, in addition to the SD mode, as a method of increasing the compression density, a NTSC video signal and a PAL video signal are both handled as a 3: 1: 0 digital video data format, and a high-density compression mode (hereinafter, “SDL mode”) "
Is abbreviated). As a device that realizes both the SD mode and the SDL mode, it is often the case that a video data input circuit for the SD mode and a video data input circuit for the SDL mode are not provided independently, but a single circuit is commonly used. In such a case, these devices use a 4: 3 sampling rate conversion circuit for the luminance signal or a high-frequency attenuation digital filter for preventing mosquito noise caused by compression distortion.

[0003] The SD mode of the DV format and S
A conventional digital video recorder realizing the DL mode will be described with reference to the drawings. FIG. 12 is a block diagram showing the configuration of a conventional digital video recording device. In FIG. 12, reference numeral 100 denotes a digital filter having a high-frequency attenuation characteristic, 101 denotes a sampling rate conversion circuit, 102 denotes a data changeover switch, and 103 denotes compression for executing and recording compression processing corresponding to the SD mode and the SDL mode of the DV format. It is a recording unit.

[0004] This conventional digital video recording apparatus includes:
It includes a digital filter 100, a sampling rate conversion circuit 101, a data changeover switch 102, and a compression recording unit 103. Then, the input luminance data of the sampling rate of 13.5 MHz (hereinafter referred to as “input luminance data”) is supplied to the first input terminal of the data changeover switch 102 via the digital filter 100 and the sampling rate conversion circuit 101. At the same time, the data is directly supplied to the second input terminal of the data changeover switch 102. The data changeover switch 102 selects the input luminance data supplied directly to the second input terminal in the SD mode and supplies it to the compression recording unit 103, and the sampling rate supplied to the first input terminal in the SDL mode. The output data of the conversion circuit 101 is selected and the compression
3 to be supplied.

In the conventional digital video recording apparatus configured as described above, the operations include a recording operation in the SD mode and a recording operation in the SDL mode. First, the recording operation in the SD mode will be described. Input luminance data having a sampling rate of 13.5 MHz is supplied to the compression recording unit 103 via the data switch 102. In the compression recording unit 103, the DV
Performs compression processing according to the SD mode of the format,
The compressed data is recorded on a recording medium. Now, it is assumed that the supply source of the input luminance data is a video camera, and its frequency characteristic is about 5 MHz as shown in FIG.
It is assumed that the frequency band is flat and gradually attenuated in a band of 5 MHz or more. The compression recording unit 103 has a flat recording capability up to about 6 MHz in the SD mode.
The video data of the video camera is compressed and recorded without deteriorating its characteristics from FIG. FIG.
3, the right end of the horizontal axis indicating the frequency is 6.75 MHz.

Next, the recording operation in the SDL mode will be described. The input luminance data having a sampling rate of 13.5 MHz is subjected to a high frequency component attenuated by the digital filter 100, and then the sampling rate conversion circuit 101
Is converted into luminance data having a sampling rate of 10.125 MHz and supplied to the compression recording unit 103 via the data changeover switch 102. In the compression recording unit 103, D
A compression process is performed in accordance with the V format SDL mode, and the compressed data is recorded on a recording medium.

Here, the sampling rate conversion circuit 10
FIG. 14 shows the frequency characteristic of No. 1. In the SDL mode, the sampling rate of the recording data is 10.125 MHz.
It has the characteristic of sufficiently attenuating the band above z. However, since the data compression ratio is high in the SDL mode, compression distortion is generated even when the high-frequency component of the frequency component of 5 MHz or less is large, and as a result, a noise component called mosquito noise is generated and image quality is deteriorated. It will be. Now, the digital filter 10
The transfer function H _{10 0} of 0 (z) is,

[0008]

It is assumed that H ₁₀₀ (z) = (1 + 14z ⁻¹ + z ⁻² ) / 16. At this time, the transfer characteristic is

[0009]

H ₁₀₀ (ω) = {7 + cos (ωT)} / 8. Here, T is a sampling cycle, and T = 1/1
3.5 MHz. The frequency characteristic of the digital filter 100 is approximately 1.6 dB at 4 MHz as shown in FIG.
It has a high-frequency attenuation characteristic having an attenuation amount of.

The output of the video camera having the frequency characteristics shown in FIG. 13 is converted into a digital filter 100 having the characteristics shown in FIG.
The result of conversion by the sampling rate conversion circuit 101 having the characteristics shown in FIG. 14 is obtained as data having an attenuation of about 1.6 dB at 4 MHz and a sufficient attenuation at 5 MHz as shown in FIG. It is designed to realize an optimum recording characteristic that keeps the resolution of a video camera as much as possible while appropriately suppressing the occurrence of mosquito noise.

The internal structure of the digital filter 100 is shown in FIG. As shown in FIG. 17, the digital filter 100 includes delay units 104 and 105, adders 106 and 107, a multiplier 108 having a gain of 1/16,
And a multiplier 109 having a gain of 7/8.

[0012]

In the above-mentioned conventional digital video recording apparatus, when a video camera having the frequency characteristics shown in FIG. 13 is used as a video data supply source, optimal compression recording can be realized when data is input. Therefore, it is required that all the other video data supply sources to which data is to be input have the same characteristics as those in FIG. Further, when the conventional digital video recording device is realized by an LSI, and when connected to a video data supply source having characteristics different from those in FIG. 13, some circuit for correcting the characteristics is required outside the LSI.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a digital video recording apparatus which can always realize optimum recording characteristics even when connected to a video data supply source having arbitrary characteristics and is suitable for LSI. .

[0014]

According to a first aspect of the present invention, there is provided a digital video recording apparatus comprising: a digital filter having a plurality of switchable high-frequency attenuation characteristics; and a sampling rate converter for converting a sampling frequency of output data of the digital filter. And a compression recording unit for compressing and recording output data of the sampling rate conversion circuit.

According to this configuration, an appropriate high-frequency attenuation characteristic is set in the digital filter in accordance with the characteristics of the video data supply source that supplies the video data to the digital filter of the video camera or the like, so that any video data can be supplied. Also in the combination with the source, the total characteristic of the frequency characteristic of the video data supply source, the frequency characteristic of the digital filter, and the frequency characteristic of the sampling rate conversion circuit can be set as the optimal characteristic for the compression format.

According to a second aspect of the present invention, there is provided a digital video recording apparatus having a plurality of switchable digital filters having a high-frequency attenuation characteristic and a high-frequency emphasis characteristic, and a sampling rate conversion circuit for converting a sampling frequency of output data of the digital filter. A switch for inputting output data of the digital filter and output data of the sampling rate conversion circuit to select and output one of them; and a compression recording unit for compressing and recording the output data of the switch. ing.

According to this configuration, an appropriate high-frequency attenuation characteristic is set in the digital filter according to the characteristics of the video data supply source that supplies the video data to the digital filter of the video camera or the like. Also in the combination with the source, the total characteristic of the frequency characteristic of the video data supply source, the frequency characteristic of the digital filter, and the frequency characteristic of the sampling rate conversion circuit can be set as the optimal characteristic for the compression format. Furthermore, by having a plurality of high-frequency emphasis characteristics that can be switched to a digital filter, when implementing a plurality of compression formats, optimal characteristics can always be realized in any of them.

[0018]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a block diagram showing a configuration of a digital video recording device according to an embodiment of the present invention. In FIG. 1, 1 is a characteristic switching signal S ₁ ,
The high-frequency characteristic switchable digital filter by S _2,
Reference numeral 2 denotes a sampling rate conversion circuit, 3 denotes a data changeover switch, and 4 denotes a compression recording unit that executes and records a compression process corresponding to the SD mode and the SDL mode of the DV format.

The digital video recording apparatus according to the present embodiment includes a digital filter 1, a sampling rate conversion circuit 2, a data switch 3, and a compression recording section 4. The data changeover switch 3 has a first input terminal connected to the output of the sampling rate conversion circuit 2, a second input terminal connected to the output of the digital filter 1, and a first input terminal in the SDL mode. The output data of the sampling rate conversion circuit 2 supplied to the digital filter 1 is selected and supplied to the compression recording unit 4. In the SD mode, the output data of the digital filter 1 supplied to the second input terminal is selected and the compression recording unit 4 is selected. 4 to be supplied. Therefore, the sampling rate 13.5M
Hz input luminance data is supplied to the compression recording unit 4 via the digital filter 1, the sampling rate conversion circuit 2 and the data switch 3 in the SDL mode, and is supplied to the digital filter 1 in the SD mode.
Is supplied to the compression recording unit 4 via the data changeover switch 3.

FIG. 2 is a diagram showing the internal configuration of the digital filter 1. This digital filter 1 has a high-pass FI.
R filter 5, sign inverter 12, characteristic switch 1
3. It is composed of a variable gain multiplier 14 and an adder 15. The high-pass FIR filter 5 includes a delay unit 6, a delay unit 7, an adder 8, an adder 9, and a gain of -0.25.
, And a multiplier 11 with a gain of 0.5, and its transfer function H _h (z) is

[0021]

H _h (z) = (− 1 + 2z ⁻¹ −z ⁻² ) / 4, and its transfer characteristic is

[0022]

Equation 4] are configured such that _{H h (ω) = {1} -cos (ωT)} / 2. Either output data of the high-pass FIR filter 5 (output data of the adder 9) or data obtained by inverting the sign of the output data by the sign inverter 12 is selected by the characteristic changeover switch 13. Characteristic switch 1
The output of the digital filter 1 is output from the digital filter 1 after being added to the output of the delay unit 6 by the adder 15 after passing through the variable gain multiplier 14 having a gain of N / 16. Note that the characteristic changeover switch 13 outputs a characteristic changeover signal S ₁
When the instruction of the characteristic switching signal S ₁ has no sign inversion, the output data of the high-pass FIR filter 5 is selected. When the instruction of the characteristic switching signal S ₁ has the sign inversion, the sign invertor 12 is selected. Select the output data of Gain N / 16 of the variable gain multiplier 14 is switched by the characteristic switching signal S ₂ for instructing the N. The characteristic switching signals S ₁ and S ₂ are supplied from outside as preset values.

In the digital video recording apparatus of the present embodiment configured as described above, the operation includes a recording operation in the SD mode and a recording operation in the SDL mode as in the conventional example. Here, a case where each of the first video camera and the second video camera having different frequency characteristics is a video data supply source will be described. First, a case where the first video camera is a video data supply source will be described. As shown in FIG. 3, the first video camera has a frequency characteristic that is flat to about 5 MHz and is smoothly attenuated in a band of 5 MHz or more. 1. In FIG. 3, the right end of the horizontal axis indicating the frequency is 6.75 MHz.

The recording operation in the SD mode in this case will be described. Sampling rate input luminance data of 13.5MHz is being treated with high-pass FIR filter 5 at the inside of the digital filter 1, gain zero in this case is characteristic switching signal S ₂ to the variable gain multiplier 14, ie, N = 0. At this time, since the output of the variable gain multiplier 14 is always zero, the input luminance data is delayed by one sample in the delay unit 6 and then the adder 15
Is output from the digital filter 1 only by adding zero, and is supplied to the compression recording unit 4 via the data changeover switch 3 while maintaining the frequency characteristics of FIG. The compression recording unit 4 performs a compression process in accordance with the SD mode of the DV format, and records the compressed data on a recording medium. Since the compression recording unit 4 has a flat recording capability up to about 6 MHz in the SD mode, the video data of the first video camera is compression-recorded without impairing its characteristics from FIG.

Next, the recording operation in the SDL mode will be described. Input luminance data at a sampling rate of 13.5 MHz is attenuated by a digital filter 1 at a high frequency component, and then converted to luminance data at a sampling rate of 10.125 MHz by a sampling rate conversion circuit 2 and compressed via a data switch 3. It is supplied to the recording unit 4. In the compression recording unit 4, the SD of the DV format is used.
The compression process is performed according to the L mode, and the compressed data is recorded on a recording medium.

Note that, inside the digital filter 1,
According to the instruction of the characteristic switching signal S ₁ , either the data whose sign of the output of the high-pass FIR filter 5 is inverted by the sign inverter 12 or the data whose sign is not inverted is selected by the characteristic switch 13. , Variable gain multiplier 14
Are multiplied by N / 16, and the output of the delay unit 6 and the adder 15 are added and output. Therefore, the transfer function H ₁ (z) of the digital filter 1 is expressed as follows when the characteristic switching signal S ₁ indicates that the sign is inverted.

[0027]

H ₁ (z) = z ⁻¹ − (− 1 + 2 z ⁻¹ −z ⁻² ) × N / 64, and the transfer characteristic is:

[0028]

H ₁ (ω) = 1− {1−cos (ωT)} × N / 32, and when the characteristic switching signal S ₁ indicates no sign inversion,

[0029]

H ₁ (z) = z ⁻¹ + (− 1 + 2z ⁻¹ −z ⁻² ) × N / 64, and the transfer characteristic is

[0030]

H ₁ (ω) = 1 + {1−cos (ωT)} × N / 32 Here, it is assumed that the characteristic switching signal S ₁ indicates that the sign is inverted, and the characteristic switching signal S ₂ indicates N = 4. At this time, the transfer function H of the digital filter 1
₁ (z) is

[0031]

H ₁ (z) = (1 + 14z ⁻¹ + z ⁻² ) / 16 The transfer characteristic is

[0032]

H ₁ (ω) = {7 + cos (ωT)} / 8, and as shown in FIG. 4, a high-frequency attenuation characteristic having an attenuation of about 1.6 dB at 4 MHz is obtained. The frequency characteristic of the sampling rate conversion circuit 2 is shown in FIG. 5, which is the same as the characteristic of the conventional example shown in FIG. The output of the first video camera having the frequency characteristics shown in FIG. 3 is attenuated in a high band by the digital filter 1 having the characteristics shown in FIG. 4, and converted by the sampling rate conversion circuit 2 having the characteristics shown in FIG.
As shown in FIG. 6, the attenuation of about 1.6 dB at 4 MHz, 5
Since data having a sufficient attenuation is obtained at MHz, it is possible to realize an optimum recording characteristic that keeps the resolution of the first video camera as much as possible while appropriately suppressing the occurrence of mosquito noise.

Next, a case where the second video camera is a video data supply source will be described. As shown in FIG. 7, the second video camera has a frequency characteristic that the DC component has already been attenuated by about 0.75 dB at 4 MHz and has been smoothly attenuated in a higher band. Input luminance data is supplied to the digital filter 1 from the video camera. In FIG. 7, the right end of the horizontal axis indicating the frequency is 6.75 MHz.

The recording operation in the SD mode in this case will be described. Characteristic switching signal S ₁ is unsigned inverted to the digital filter 1, characteristic switching signal S ₂ instructs the N = 2. At this time, the transfer function H of the digital filter 1
₁ (z) is

[0035]

H ₁ (z) = (− 1 + 34 z ⁻¹ −z ⁻² ) / 32, and the transfer characteristic is

[0036]

H ₁ (ω) = {17−cos (ωT)} / 16, and as shown in FIG. 8, the high-frequency enhancement characteristic of about 0.67 dB at 4 MHz is obtained. The result of processing the output of the second video camera having the frequency characteristic of FIG. 7 by the digital filter 1 whose characteristic of FIG. 8 is delayed is 4 MHz as shown in FIG.
z can be made almost flat, and the compression recording unit 4
Compresses and records the result in the SD mode, so that even if a second video camera having a lower resolution and a lower high-frequency region than the first video camera is used, the resolution is further improved and
D recording can be realized. Note that FIG.
, The right end of the horizontal axis indicating frequency is 6.75 MHz.

Next, the recording operation in the SDL mode will be described. Characteristic switching signals S ₁ to the digital filter 1 there sign inversion, characteristic switching signal S ₂ instructs the N = 2. At this time, the transfer function H ₁ (z) of the digital filter 1 is

[0038]

H ₁ (z) = (1 + 30z ⁻¹ + 1z ⁻² ) / 32 The transfer characteristic is

[0039]

H ₁ (ω) = {15 + cos (ωT)} / 16, and approximately 0.73 dB at 4 MHz as shown in FIG.
High-frequency attenuation characteristic having an attenuation amount of Since the characteristics of the sampling rate conversion circuit 2 are as shown in FIG.
The output of the second video camera having the frequency characteristics of FIG.
The result of high-frequency attenuation by the digital filter 1 having the characteristic of 0 and conversion by the sampling rate conversion circuit 2 having the characteristic of FIG. 5 is about 1.times.1 at 4 MHz as shown in FIG.
Data having an attenuation of 5 dB and a sufficient attenuation at 5 MHz can be obtained, and the optimum recording characteristics for maintaining the resolution as much as possible while appropriately suppressing the occurrence of mosquito noise can be realized.

As described above, according to the present embodiment, the digital filter 1 is provided with a plurality of selectable high-frequency attenuation characteristics, and the processing result is subjected to the sampling rate conversion by the sampling rate conversion circuit 2 to record in the SDL mode. The optimal high-frequency attenuation can be set in advance according to the characteristics of the video camera that is the video data supply source that supplies the luminance data. Recording can be realized.

The digital filter 1 also has a plurality of selectable high-frequency emphasis characteristics, so that
Not only in the DL mode but also in the SD mode, it is possible to compensate for the insufficient resolution according to the characteristics of the video camera as the video data supply source, and easily realize higher quality image recording. In the present embodiment, the characteristic switching signals S ₁ and S ₂ are supplied from a microcomputer.
Alternatively, it is supplied fixedly by a wiring pattern on a printed circuit board. When composing the digital video recording apparatus of the present embodiment and a video camera to form one product, it is optimal to incorporate a characteristic switching signal into microcomputer software or a wiring pattern on a printed circuit board in accordance with the characteristics of the video camera. Can be realized. Further, even in the case of combining with a video camera having different characteristics, optimization can be easily realized by only partially changing the software or the wiring pattern. That is, even if an arbitrary range from the digital filter 1 to the compression recording unit 4 is realized by an LSI, no additional mechanism is required in combination with any video data supply source.

In the present embodiment, the digital filter 1 is configured to have the high-pass FIR filter 5 having the transfer function of Equation 3, but the FIR filter having another order and another transfer function is used. May be provided.
Further, in the present embodiment, a video camera has been described as an example of a video data supply source, but a configuration in which the video camera is connected to another video data supply source may be used, or a configuration in which a plurality of video data supply sources are switched and connected. Is also good.

Also, in the present embodiment, only the luminance data is input to the digital filter 1,
For other video data, that is, color difference data (C _r , C _b ), signal processing such as 2: 2 and 1: 1, 2: 2 and 2: 0, 2: 2 and 1: 0, etc. are all simple. This can be realized by performing filter thinning and interpolation, and the configuration of the present embodiment is unnecessary.

[0044]

As described above, according to the present invention, a digital filter having a plurality of switchable high-frequency attenuation characteristics,
A sampling rate conversion circuit for converting a sampling frequency of output data of the digital filter, wherein the high-frequency attenuation characteristic of the digital filter is optimally set according to a characteristic of a video data supply source for supplying video data to the digital filter. Therefore, in any combination with any video data source, the overall characteristics of the frequency characteristics of the video data source, the frequency characteristics of the digital filter, and the frequency characteristics of the sampling rate conversion circuit are determined as the optimal characteristics for the compression format. Is what you can do. In addition, by providing a plurality of high-frequency emphasis characteristics that can be switched to a digital filter, when realizing a plurality of compression formats, optimum characteristics can always be realized in any of them. Further, since it is suitable for LSI and can be applied to a plurality of products connected to different video data supply sources using the same LSI without an external additional circuit, it is industrially advantageous that it can be realized at extremely low cost. Effects can be obtained.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a digital video recording device according to an embodiment of the present invention.

FIG. 2 is a configuration diagram of a digital filter 1 according to the embodiment of the present invention.

FIG. 3 is a frequency characteristic diagram of a first video camera that supplies luminance data according to the embodiment of the present invention.

FIG. 4 is a frequency characteristic diagram of an SDL mode for a first video camera of the digital filter 1 according to the embodiment of the present invention.

FIG. 5 is a frequency characteristic diagram of the sampling rate conversion circuit 2 according to the embodiment of the present invention.

FIG. 6 is an overall frequency characteristic diagram of an SDL mode for the first video camera according to the embodiment of the present invention.

FIG. 7 is a frequency characteristic diagram of a second video camera that supplies luminance data in the embodiment of the present invention.

FIG. 8 is a frequency characteristic diagram of an SD mode for a second video camera of the digital filter 1 according to the embodiment of the present invention.

FIG. 9 is a total frequency characteristic diagram of an SD mode for a second video camera according to the embodiment of the present invention.

FIG. 10 is a frequency characteristic diagram of an SDL mode for a second video camera of the digital filter 1 according to the embodiment of the present invention.

FIG. 11 is an overall frequency characteristic diagram of the SDL mode for the second video camera according to the embodiment of the present invention.

FIG. 12 is a configuration diagram of a conventional digital video recording device.

FIG. 13 is a frequency characteristic diagram of a video camera that supplies luminance data in a conventional example.

FIG. 14 is a frequency characteristic diagram of a sampling rate conversion circuit 101 in a conventional example.

FIG. 15 is a frequency characteristic diagram of a digital filter 100 according to a conventional example.

FIG. 16 is an overall frequency characteristic diagram of an SDL mode in a conventional example.

FIG. 17 is a configuration diagram of a digital filter 100 in a conventional example.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Digital filter 2 Sampling rate conversion circuit 3 Data changeover switch 4 Compression recording part 5 High-pass type FIR filter 6,7 Delayer 8,9,15 Adder 10,11 Multiplier 12 Sign inverter 13 Characteristic changeover switch 14 Variable Gain multiplier

Claims (2)

[Claims] 1. A digital filter having a plurality of switchable high-frequency attenuation characteristics, a sampling rate conversion circuit for converting a sampling frequency of output data of the digital filter, and compressing and recording output data of the sampling rate conversion circuit. A digital video recording device comprising a compression recording section. 2. A digital filter having a plurality of switchable high-frequency attenuation characteristics and high-frequency emphasis characteristics, a sampling rate conversion circuit for converting a sampling frequency of output data of the digital filter, and output data of the digital filter. A digital video recording apparatus, comprising: a changeover switch for inputting output data of the sampling rate conversion circuit to select and output one of them; and a compression recording section for compressing and recording the output data of the changeover switch.