JPH10327339A - Signal processor and recorder - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a moving/still images of high definition by making a low- pass filter process an inputted analog image signal at a first cut-off frequency at the time of moving picture mode and a second cut-off frequency process at a cut-off frequency higher than the first cut-off frequency at the time of a still image mode. SOLUTION: A control part 111 controls a memory control circuit 113 and a recording circuit to record a moving image and a still image according to the switching of moving picture mode and a still image mode from an operation part 112. In addition, the part 111 controls a filter control circuit 100 and sets the cut-off frequency of LPF 103 so as to show the suppressing characteristic of -12 dB degree at the 1/2 frequency of a sampling frequency at the time of a still image mode and to set to be lower at the time of the moving picture mode than the still picture mode. Thereby, the still image of high definition is obtained to suppress the noise generated in a moving image signal.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

[0001] 1. Field of the Invention [0002] The present invention relates to a signal processing apparatus and a recording apparatus, and more particularly to an apparatus for processing and recording an analog image signal by converting it into a digital signal.

[0002]

2. Description of the Related Art In recent years, as a device of this type, a device for recording a digital video signal on a tape or a disk has rapidly spread on a consumer level. Examples of this type of device include a digital video camcorder (DVC) conforming to the DVC format standard, and a DVD player for reproducing a digital video disk (DVD) in which a video signal compressed and encoded according to the MPEG standard is recorded on an optical disk. Can be

[0003] In particular, in DVC, not only a function of recording and reproducing a digital video signal but also a function of recording an analog video signal inputted from the outside as a digital signal is desired.

[0004]

By the way, the above-mentioned DV
C generally realizes a recording / reproducing function of a still image in addition to a recording / reproducing of a normal moving image.

[0005] However, in DVC, when a digital video signal is compression-encoded, block encoding using DCT is performed. However, mosquito noise is a characteristic noise when a moving image signal is compression-encoded by block encoding. Noise occurs. This mosquito noise is noise generated in the form of an edge at the boundary between blocks and is inconspicuous in a scene where the image has relatively little movement, but has a characteristic that it is easily noticeable in a scene where the image has movement.

On the other hand, with respect to a still image, not only the visual characteristics are improved by a television monitor, but also the image quality such as resolution and S / N when output by a printer is changed from a viewpoint different from that of a moving image. It is required to increase.

As described above, there are specific problems in improving the quality of a moving image and a still image. However, especially when an analog video signal input from the outside is recorded as a moving image and a still image, these problems occur. Need to solve the problem.

An object of the present invention is to solve the above-mentioned problems.

Another object of the present invention is to obtain a high-definition moving image and still image.

[0010]

SUMMARY OF THE INVENTION In order to solve the above problems and achieve the object, the present invention relates to a device for inputting an analog image signal and converting it into a digital image signal. Band limiting means for limiting the frequency band, and converting means for sampling an analog image signal band-limited by the band limiting means in accordance with a clock of a predetermined frequency, and converting the analog image signal into a digital image signal having a predetermined number of bits per sample. A first mode in which the limiting unit limits the band of the analog image signal with a first characteristic, and the converting unit samples the analog image signal in accordance with the clock of the predetermined frequency; The band of the analog image signal is limited by a second characteristic different from the characteristic, and the conversion unit operates at the predetermined frequency. It is configured to have a second mode for sampling the analog image signal according to the lock.

In another aspect of the present invention, a low-pass filter for filtering an input analog image signal, an A / D converter for converting an analog image signal processed by the low-pass filter into a digital image signal, /
Recording means for recording the digital image signal obtained by the D conversion means on a recording medium, wherein the low-pass filter processes the analog image signal at a first cutoff frequency, and wherein the recording means A moving image mode for recording a signal as a moving image, wherein the low-pass filter processes the analog image signal at a second cutoff frequency higher than the first cutoff frequency, and the recording unit converts the digital image signal to And a still image mode for recording as a still image.

[0012]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a block diagram showing a configuration of a DVC to which the present invention is applied.

In FIG. 1, an analog image signal input from an imaging unit 101 is amplified to a predetermined signal level by an amplifier 102 and output to an LPF 103. LPF is A
This is a pre-filter for suppressing aliasing noise generated by the / D converter 105, and its characteristics are controlled by the filter control circuit 110 as described later.

The image signal filtered by the LPF 104 is subjected to an A / D converter 105 by a clamp circuit 104.
The signal potential is adjusted so as to be suitable for the input range.
Specifically, for example, the reference pedestal level (black level) is adjusted to have a constant DC potential even if the average luminance level of the image signal fluctuates.

The A / D converter 105 operates in accordance with the sampling clock of the sampling frequency f _s to generate the clamp circuit 10.
The analog image signal processed in step 4 is sampled, converted into a digital signal of 8 bits per sample, and output to the memory unit 106. The memory unit 106 includes a memory capable of storing digital image signals for a plurality of frames (two frames in this embodiment) and a shift register provided at an input stage thereof, and a memory control circuit 116.
The digital signal from the A / D converter 105 is stored in accordance with the output control signal.

The digital image signal stored in the memory unit 106 is read out by the memory control circuit 116 in an address order different from the address order at the time of writing so that the data order is suitable for the subsequent compression / encoding processing. Are output to the compression / encoding circuit 107. Compression / encoding circuit 107
Performs a well-known process such as DCT and variable-length coding on the digital image signal read from the memory unit 106 to compress the amount of information and output it to the recording processing circuit 108.

The recording processing circuit 108 is a compression / encoding circuit 1
In addition to adding data such as sync data and ID data to the image signal coded by 07, the image signal is error-correction-coded by adding parity data, and further subjected to a digital modulation process suitable for recording. Output to The recording circuit 109 includes a rotary head for tracing the magnetic tape to record and reproduce signals, and also includes a drive circuit for transporting the tape. The recording circuit 109 transports the tape at a predetermined speed under the control of the control unit 111 as described later, The digital signal processed by the processing circuit 108 is recorded on a tape by a rotating head.

The DVC according to the present embodiment has a moving image mode for recording a moving image and a still image mode for recording a still image. The user switches each mode by operating a mode switch of the operation unit 112.

The control unit 111 controls the memory control circuit 113 and the recording circuit 109 according to the mode, and records a moving image and a still image.

That is, in the moving image mode, the input moving image signal is sequentially written to the memory 106 as a digital signal, and the reading is repeated, thereby repeating the recording circuit 109.
Output to The recording circuit 109 conveys the tape at a predetermined speed and records a moving image signal on the tape.

In the still image mode, the control unit 111 stops writing the image signal to the memory unit 106 in response to the operation of the recording trigger switch in the operation unit 112, and the memory unit 106 The image signal is repeatedly read and output to the recording circuit 109 as a still image signal. On the other hand, the recording circuit 109 conveys the tape, and after recording the still image signal output from the memory unit 106 for several seconds, for example, 5 seconds, stops the tape conveyance.

In this embodiment, L is set according to the recording mode of the apparatus.
The characteristics of the PF 103 are changed. That is, the control unit 111
Controls the filter control circuit 110 to change the characteristics of the LPF 103 between the case where the moving image mode is designated and the case where the still image mode is designated by the user using the operation unit 112 as described below.

FIG. 2 is a diagram showing the amplitude characteristic of the LPF 103.

In the figure, reference numeral 201 denotes L in the still image mode.
Shows the amplitude characteristic of PF103, the cut-off frequency is f _c1, also shows the suppression characteristic of about αdB at half the frequency of the sampling clock. Is usually about -12 dB, but can be changed as appropriate according to the system configuration.

Reference numeral 202 denotes the LPF 10 in the moving image mode.
3 shows an amplitude characteristic, and the cutoff frequency is a frequency _fc2 lower than that in the still image mode.

In this embodiment, the filter 103
Of the filter 103 in the moving image mode.
Since the cut-off frequency is lower than that in the still image mode, it is possible to suppress the occurrence of mosquito noise accompanying the compression and encoding of the moving image signal.

On the other hand, since the cutoff frequency of the still image signal is not lowered as in the moving image mode, a still higher definition still image can be obtained.

FIG. 3 is a diagram showing the configuration of the LPF 103.

In the figure, reference numeral 301 denotes a transconductance amplifier (hereinafter referred to as a Gm amplifier); 702, a buffer;
03 is a capacitor.

Normally, an active LPF as a filter with a built-in IC is designed so as to obtain desired filter characteristics by connecting the LPF composed of a Gm amplifier + a capacitor + a buffer in multiple stages as shown in FIG.

In the present embodiment, the Gm amplifier 301 and the capacitor 303

[0033]

[Outside 1] LPF. In the LPF of FIG. 3, the cutoff frequency of the LPF 103 can be continuously changed by controlling the current of the Gm amplifier 301. In the present embodiment, control current values for the moving image mode and the still image mode are set in advance, and the filter control circuit 110 controls the Gm amplifier 301 with each current value in accordance with a mode switching instruction from the control unit 111, and cuts off. The frequency has changed.

Next, the group delay characteristic of the filter 103 will be described.

FIG. 4 is a diagram showing the group delay characteristics of the filter 103. Reference numeral 401 denotes the group delay characteristics in the still image mode. In the present embodiment, the group delay characteristic in the still image mode is set to D ₁ nS in the pass band. Here, the frequency f _s of the sampling clock of the A / D converter 105 is assumed to be 13.5 MHz, D ₁ is 300
It is about 800 ns.

Reference numeral 402 denotes a group delay characteristic of the filter 103 in the moving image mode.

As described above, the group delay characteristic in the pass band of the filter 103 is changed in accordance with the mode switching. In this embodiment, however, the difference (D ₂ −D ₁ ) in the group delay time between the modes. Is an integral multiple of the sampling period in the A / D converter 105.

[0038]

[Outside 2] Is set.

For example, when the frequency of the sampling clock of the A / D converter 105 is 13.5 MHz, the delay time difference (D ₂ −D ₁ ) of the filter 103 is:

[0040]

[Outside 3] Becomes

As described above, even if the group delay characteristic changes between the modes, if the delay time difference is an integer multiple of the sampling clock cycle, the delay error can be easily adjusted when writing to the memory 106.

That is, in this embodiment, a shift register that operates with a sampling clock is provided at the input stage of the memory in the memory unit 106, and the control unit 111 controls the memory control circuit 113 to shift the shift amount in the shift register according to the mode. Is changed, the writing timing of the digital image signal to the memory is adjusted, and the change in the group delay characteristic accompanying the change in the filter characteristic is adjusted.

As described above, in the present embodiment, the cut-off frequency of the filter 103 in the moving image mode is made lower than that in the still image mode by controlling the characteristics of the filter in accordance with the mode. Mosquito noise caused by compression and encoding of
Further, since the cutoff frequency of the still image signal is not reduced as in the case of the moving image mode, it is possible to obtain a higher definition still image.

FIG. 5 is a diagram showing another example of the configuration of the filter 103.

In FIG. 5, 501 and 503 are capacitors, 502 is a switch, and 504 is an amplifier.

In the filter shown in FIG.
The cut-off frequency can be controlled by a switched capacitor in which the switch 01 and the switch 502 are combined. The switched capacitor is a technology that realizes an element equivalent to a resistor by combining a capacitor and a switch and controlling opening and closing of the switch at high speed.

[0047] In FIG. 5, a switch 502 cycle T _s
Is switched alternately between the a side and the b side. At this time, when the capacitance of the capacitor 501 and C _1,

[0048]

[Outside 4] Holds.

Therefore, the switch 502 is set to 1 / T _s [H
z], a resistance value R corresponding to the frequency can be obtained by controlling with a signal having a frequency of z].

Therefore, in the configuration of FIG.

[0051]

[Outside 5] Can achieve become LPF, f _c can be continuously variably controlled in accordance with the frequency of the control signal of the switch 502.

In this embodiment, the cutoff frequency is changed by setting the frequencies for the moving image mode and the still image mode in advance and switching the frequency of the control signal of the switch 502 according to the mode.

The characteristics of the filter may be changed as shown in FIG.

That is, in FIG. 6, reference numerals 601 and 602 denote filters 10 in the still image mode and the moving image mode, respectively.
3, the shoulder characteristic of the filter (Q: Qualit
y Factor) is different. Filter control circuit 110
Changes the shoulder characteristic as 602 by lowering the Q of the circuit in the moving image mode.

[0055]

As described above, when the digital signal is obtained from the analog signal, the signal processing apparatus of the present invention has two modes for filtering the analog signal with different filter characteristics and performing sampling with the same sampling clock. , It is possible to obtain an optimal digital signal according to the subsequent processing mode.

Further, in the recording apparatus of the present invention, the characteristics of the filter are switched between a moving image mode in which a digital signal is recorded as a moving image and a still image mode in which a digital signal is recorded as a still image. Digital signal can be obtained.

In particular, a higher definition still image can be obtained by increasing the cutoff frequency of the filter in the still image mode as compared with the moving image mode.

In the moving image mode, the noise generated in the moving image signal can be suppressed by lowering the cutoff frequency.

[Brief description of the drawings]

FIG. 1 is a diagram showing a configuration of a digital VTR as an embodiment of the present invention.

FIG. 2 is a diagram illustrating a frequency characteristic of the LPF of FIG. 1;

FIG. 3 is a diagram showing a configuration of the LPF of FIG. 1;

FIG. 4 is a diagram illustrating a group delay characteristic of the LPF of FIG. 1;

FIG. 5 is a diagram illustrating another configuration of the LPF of FIG. 1;

FIG. 6 is a diagram illustrating another frequency characteristic of the LPF of FIG. 1;

[Explanation of symbols]

 103 LPF 110 filter control circuit 111 control unit

Claims (14)

[Claims] 1. An apparatus for inputting an analog image signal and converting it into a digital image signal, comprising: a band limiting unit for limiting a band of the input analog image signal; and an analog image signal band-limited by the band limiting unit. Is sampled according to a clock of a predetermined frequency,
Converting means for converting the digital image signal into a digital image signal having a predetermined number of bits per sample, wherein the band limiting means limits the band of the analog image signal with a first characteristic, and the converting means converts the analog signal according to a clock having the predetermined frequency. A first mode for sampling an image signal, wherein the band limiting unit limits the band of the analog image signal with a second characteristic different from the first characteristic, and the conversion unit performs the operation according to the clock having the predetermined frequency. A second mode for sampling an analog image signal. 2. In the first mode, the band suppression means limits the band of the analog image signal at a first limit frequency, and in the first mode, a second band higher than the first frequency. 2. The signal processing apparatus according to claim 1, wherein a band of the analog image signal is limited at a limited frequency. 3. The signal processing apparatus according to claim 2, wherein each of the first limited frequency and the second limited frequency is near a half of the predetermined frequency. 4. A recording device for recording a digital image signal output from the conversion device on a recording medium, wherein the recording device records the digital image signal processed in the first mode as a moving image, The signal processing apparatus according to claim 1, wherein the digital image signal processed in the second mode is recorded as a still image. 5. The signal processing apparatus according to claim 1, wherein the input unit includes an imaging unit that captures a subject image to obtain the analog image signal. 6. The signal according to claim 1, further comprising an encoding unit that divides the digital image signal into a plurality of blocks each including a predetermined number of pixels and performs block encoding on a block basis. Processing equipment. 7. A low-pass filter for filtering an input analog image signal; A / D conversion means for converting an analog image signal processed by the low-pass filter into a digital image signal; and A / D conversion means. Recording means for recording the digital image signal on a recording medium, wherein the low-pass filter processes the analog image signal at a first cutoff frequency, and the recording means records the digital image signal as a moving image. A moving image mode, wherein the low-pass filter processes the analog image signal at a second cutoff frequency higher than the first cutoff frequency, and the recording unit records the digital image signal as a still image. A recording mode having an image mode. 8. The A / D converter according to claim 7, wherein the A / D converter samples the analog image signal output from the input unit in accordance with a clock having a predetermined frequency, and outputs a digital signal having a plurality of bits per sample. The recording device according to claim 1. 9. The low-pass filter has a different group delay time between the moving image mode and the still image mode,
9. The recording apparatus according to claim 8, wherein a difference between group delay times in the moving image mode and the still image mode is an integral multiple of a cycle of the clock. 10. A delay unit for delaying a digital image signal output from the conversion unit, wherein the delay unit has a first delay time in the moving image mode, and has a first delay time in the still image mode. 10. The recording apparatus according to claim 9, wherein the recording apparatus has a second delay time different from the delay time. 11. The recording apparatus according to claim 10, wherein said delay means operates according to said clock. 12. The recording apparatus according to claim 8, wherein the A / D converter samples the analog image signal in accordance with the clock having the predetermined frequency in both the moving image mode and the still image mode. . 13. The recording apparatus according to claim 8, wherein each of the first and second cutoff frequencies is near a half of the predetermined frequency. 14. A low-pass filter for filtering an input analog signal, and an A / D for sampling the analog signal processed by the low-pass filter according to a clock of a constant frequency and converting the analog signal into a digital signal having a predetermined number of bits per sample.
A signal processing device comprising: a conversion unit; a processing unit that processes the digital signal obtained by the A / D conversion unit; and a control unit that determines a cutoff frequency of the low-pass filter according to a processing mode of the processing unit. .