JP2928886B2 - Image signal processing device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an image signal processing device that processes an image signal.

2. Description of the Related Art Conventionally, there is a still video (SV) system as a device for recording and reproducing a still image signal.

In the SV system, a current TV signal such as an NTSC television (TV) signal is FM-modulated and recorded on a magnetic disk called a video floppy. Therefore, the resolution of the image signal recorded and reproduced by the SV system is of a level conforming to the current TV system.

However, in a system that handles still image signals, such as an SV system, a reproduced image may be printed out by a printer. In this case, it has been pointed out that the image quality (particularly the resolution) is lower than that of a silver halide photograph.

Recently, new TV systems such as HDTV (High Definition TV) have been studied. This HDTV system is compatible with the current NT
It has about 1000 scanning lines, which is about twice that of the SC system, and has a horizontal signal band corresponding to the number of scanning lines.

Therefore, it has been necessary to develop a still image recording / reproducing system having a resolution of about 1000 pixels × 1000 pixels (when a square screen is extracted) as obtained in an HDTV or the like even in an SV system. .

However, when a still image signal having a high resolution of about 1000 pixels × 1000 pixels (when a square screen is extracted) is recorded on a video floppy,
The problem arises that compatibility with the SV system must be maintained.

As a method of solving such a compatibility problem, the following method is considered by the present applicant.

This method not only can record and reproduce image signals comparable to HDTV, but can also maintain compatibility with conventional SV systems, so it is compatible with CHSV (Compatible High definition Still Video).
o) We call it the method.

CHSV system, for example, the offset sampled luminance signal at the sampling interval indicated by T _s in FIG. As shown in FIG. 2 _{A i, B i, C i} , D i (i = 1,2 ·· .), Divided into four field screens, recorded on four tracks on a video floppy in a method conforming to the current SV format, and at the time of reproduction, the reproduction signal is sampled again to obtain offset-sampled luminance. After the signal is restored, the image signal is stored in the frame memory, and an image signal having a resolution of about 1300 pixels × 1000 pixels is reproduced by performing pixel interpolation using the pixel signal stored in the frame memory. Output system.

By the way, in the above-mentioned CHSV system, analog transmission of sample values as shown in FIG. 3 is realized by a transmission line constituted by an FM modulation / demodulation and electromagnetic conversion system and resampling performed during reproduction.

However, actually, the shape of the sample value sequence input to the transmission line is not an impulse shape as shown in FIG. 3, but has a finite width as shown in FIG. Because of the characteristic (Nyquist characteristic), it is necessary to perform aperture correction on the signal passing through the transmission path as shown in FIG. 4 so that the signal can be correctly restored.

In order to perform analog transmission of sample values correctly, the transmission path must have low-pass filter characteristics and correct resampling must be performed on the receiving side.

In particular, if the above condition is not satisfied, ringing occurs near the edge of the image, and the reproduced image is significantly deteriorated.

Therefore, in order to perform correct resampling on the receiving side, a signal serving as a phase reference for resampling is added to the transmission image signal, and resampling is performed on the receiving side according to the phase reference signal added to the transmission image signal. You need to control the transport.

FIG. 5 is a diagram showing a schematic configuration of a reproducing apparatus conforming to the CHSV system. For the sake of simplicity, it is assumed that the reproducing apparatus shown in FIG. 5 reproduces the monochrome image signal from a video floppy on which the monochrome image signal is recorded in accordance with the CHSV method. In FIG. 5, the video floppy 50
The signal recorded in 1 is reproduced by the reproduction head 502 and supplied to the reproduction processing circuit 503. The reproduction processing circuit 503 performs FM modulation, de-emphasis processing, and the like on the supplied signal, and outputs the signal as a reproduced image signal. Then, the reproduced image signal is subjected to an aperture correction process in an aperture correction filter 505 and a clamp process in a clamp circuit 506, and then supplied to an analog / digital (A / D) converter 507.

On the other hand, in the resampling clock generation circuit 504,
TBC (Time Base Corrector) recorded from the signal reproduced by the reproducing head 502 from the video floppy 501 by being frequency-multiplexed with the image signal during recording
Only the separated use pilot signal component, by a PLL re-sampling clock generating circuit 504 (Phase Locked Loop) circuit to form a re-sampling clock f _s which follows the time base fluctuations occurring on the reproduced image signal, and outputs .

Resampling clock f _s outputted from the re-sampling clock generating circuit 504 as described above variable delay circuit 50
8, the resampling phase is controlled in the variable delay circuit 508, and is supplied to the A / D converter 507.

The phase control operation of the re-sampling clock f _s in the variable delay circuit 508 is controlled by the phase control signal generating circuit 509 receives the image signal re-sampled in the phase control signal generating circuit 509, re-sampled image signal , A phase control signal PC corresponding to the sample value corresponding to the phase reference signal portion is formed, output to the variable delay circuit 508, and the phase of the resampling clock is controlled to the correct phase.

As described above, the reproduced image signal digitized by the A / D converter 507 using the resampling clock whose phase has been correctly adjusted is Nyquist-equalized by the automatic equalizer 510.

The automatic equalizer 510 is configured by a digital filter, and has a configuration capable of changing an equalization characteristic by changing a tap coefficient of the digital filter. The tap coefficient of the digital filter is changed by the coefficient control circuit 511, and the operation will be described below. The subtractor 512 includes the A / D converter 50
And resampling the image signal outputted from 7, and the ideal response waveform signal I _n generated from the oscillator (not shown) is supplied, resampling phase reference signal portion during a re-sampling the image signal from the subtracter 512 and values, the ideal response waveform signal I _n
The coefficient control circuit 511 outputs to the automatic equalizer 510 a tap coefficient selection signal for changing the tap coefficient of the digital filter in the automatic equalizer 510 according to the result of the subtraction. The optimum tap coefficient is selected in the digital filter in the unit 510, and the resampled image signal is automatically Nyquist-equalized.

The digitally reproduced image signal automatically Nyquist-equalized as described above is stored in the image memory 513.

By performing the above-described reproduction signal processing operation on the signals reproduced from each of the four tracks on the video floppy 510, the image memory 513 performs offset sampling as shown in FIG. Sample data corresponding to the luminance signal is stored.

Then, after an interpolation process is performed by the interpolation circuit 514 using the sample data stored in the image memory 513,
The stored sample data is read from the image memory 513, converted into an analog signal by a digital / analog (D / A) converter 515, and output as a reproduced monochrome still image signal via the LPF 516.

[Problems to be Solved by the Invention] By the way, as a phase reference signal added to an image signal, for example, an impulse-like signal or a step-like signal is used, and the added phase reference signal is noise during reproduction. Is generally added at about 100% level with respect to the white level of the image signal.

FIG. 6 is a diagram showing a waveform of a phase reference signal reproduced at the time of reproduction when an impalaless phase reference signal is added to an image signal at the time of recording. FIG. 7 is a diagram showing a step-like phase reference signal at the time of recording. FIG. 8 is a diagram showing a waveform of a phase reference signal reproduced at the time of reproduction when “.” Is added. As shown in FIG. 6, a signal whose level rapidly changes has a ringing component which is an excessive vibration, and such a ringing component is not limited to the phase reference signal portion but abruptly changes in the level in the image signal. This also occurs in areas where changes occur.

In addition, the reproducing apparatus conforming to the CHSV system shown in FIG. 5 is configured so that after the image signal reproduced by the A / D converter 507 is sampled, the waveform is equalized by the automatic equalizer 510. , The dynamic range of the A / D converter 507 must be set so as to correspond to a reproduced image signal before waveform equalization. That is, the A / D converter 507
The dynamic range of C in FIG. 7 is as shown in FIG.
(= A + 2 × B). Here, since the value of B in the figure can take a value of the maximum (0.2 × A), A / D
The dynamic range of the converter 507 needs to be set to about 1.4 times the dynamic range A of the input signal.

Further, the dynamic range of the A / D converter 507 is set in consideration of the deviation of the filter characteristics in the aperture correction filter 505, the change in the frequency characteristics due to the position of the reproduction track on the video floppy 501, and the like. It is necessary to set the dynamic range of the device 507 larger than the above.

However, when the dynamic range of the A / D converter is expanded and the number of quantization bits of the A / D converter is constant, quantization noise increases. For example,
As mentioned above, the dynamic range of the A / D converter is about 1.4 × A
If (A is the dynamic range of the input signal of the A / D converter), the quantization noise will increase by about 3 dB, and the image quality of the reproduced image will be degraded. However, there is a problem that the number of quantization bits is wastefully used.

The present invention has been made to solve such a problem, and an object of the present invention is to provide an image signal processing device capable of accurately and stably performing digital signal processing on an image signal.

[Means for Solving the Problems] To achieve the above object, an image signal processing apparatus according to the present invention includes a level control unit that inputs an image signal, controls a level of the input image signal, and outputs the level. Clamping means for clamping and outputting an image signal output from the level control means, conversion means for converting the image signal output from the clamping means into a digital signal, and outputting the digital signal;
Digital signal processing means for processing a digital signal output from the conversion means; and a level control characteristic in the level control means and a clamp level control characteristic in the clamp means according to the digital signal output from the conversion means. Control means.

[Operation] According to the above configuration, the image signal is accurately and stably digitally controlled by controlling the level control characteristic and the clamp level control characteristic of the image signal before being converted into the digital signal in accordance with the digital signal. The signal can be processed.

[Examples] Hereinafter, the present invention will be described using examples of the present invention. FIG. 1 is a block diagram showing a schematic configuration of a reproducing apparatus conforming to the CHSV system as one embodiment of the present invention.

In the apparatus shown in FIG. 1, the same components as those of the apparatus shown in FIG. 5 are denoted by the same reference numerals, and detailed description thereof will be omitted.

In FIG. 1, a reproduced image signal that has been subjected to aperture correction processing in an aperture correction filter 505 is supplied to an A / D converter 507 via a variable gain amplifier 101 and a clamp circuit 102, and is re-generated by the A / D converter 507. By being sampled, it is converted into a digital reproduced image signal and output.

The phase control signal generation circuit 103 includes a phase control signal PC corresponding to a sample value corresponding to a phase reference signal portion included in the digital reproduction image signal output from the A / D converter 507.
And outputs the result to the variable delay circuit 508.

In the phase control signal generation circuit 103, the A / D converter 507
It is detected whether or not the resampling phase of the digitally reproduced image signal output is correctly controlled. If the resampling phase is not correctly controlled, it is set to “0”. Is output.

Incidentally, the variable gain amplifier 101, the gain control signal V _G1 is selected by the switch S _1, V _G2 is constructed such that the gain is switched by also clamp circuit 102 is selected by the switch S ₂ clamps The configuration is such that the clamp potential is switched by the potential control signals V _R1 and V _R2 . The switches S ₁ and S ₂ are switched by the instruction signal P. When the instruction signal P indicates “0”, the switch S ₁ is a gain control signal V _G1 and the switch S ₂ is a clamp. select potential control signal V _R1, the switch S ₁ when indicating the instruction signal P is "1" in the gain control signal V
The _G2 switches S ₂ selects the clamp potential control signal V _R2.

Quantum of A / D converter 507 by switching the instruction signal P is "1" or "0" is corresponding to that setting of the respective clamp voltage control signal V _R and the gain control signal V _G as described above As shown in FIG. 8 (a) (when the instruction signal P is "0") and (b) (when the instruction signal P is "1"), the conversion range is represented by △ in FIG. (△ is a very small amount).

Incidentally, in the embodiment shown in FIG.
Gain control signal V _G and the clamp circuit 10 for controlling the gain
By switching both of the clamp potential control signal V _R which controls the second clamp potential, it has been constructed as to change the quantization range for the input signal of the A / D converter 507, a gain control signal V _G or clamp potential by switching only one of the control signals V _R, it may be configured so as to change the quantization range for the input signal of the a / D converter 507,
The configuration can be simplified as compared with the above-described example.

Also, in the present embodiment, the case where the present invention is applied to a playback device conforming to the CHSV system has been described.
The present invention is not limited to this, and the present invention is also applicable to other systems using analog transmission of sample values (for example, the MUSE system).

As described above, in this embodiment, the quantization range of the input signal of the A / D converter is switched depending on whether or not the resampling phase of the digital reproduction image signal output from the A / D converter is correct. When the sampling phase is correct, the dynamic range of the A / D converter input signal is switched so that the quantization range of the A / D converter input signal is minimized. It is possible to prevent use of the quantization bit number of the A / D converter unnecessarily.

[Effects of the Invention] As described above, according to the present invention, it is possible to provide an image signal processing apparatus capable of accurately and stably performing digital signal processing on an image signal.

[Brief description of the drawings]

FIG. 1 is a block diagram showing a schematic configuration of a reproducing apparatus conforming to the CHSV system as an embodiment of the present invention. FIG. 2 is a diagram showing sampling points of luminance signals in the CHSV system.
FIG. 4 is a diagram for explaining analog transmission of sample values, FIG. 5 is a diagram showing a schematic configuration of a reproducing apparatus conforming to the CHSV system, and FIG. 6 is an impulse-like phase reference for an image signal during recording. FIG. 7 shows a waveform of a phase reference signal reproduced during reproduction when a signal is added. FIG. 7 shows a phase reference signal reproduced during reproduction when a step-like phase reference signal is added to an image signal during recording. FIGS. 8 (a) and 8 (b) show waveforms, and FIGS. 8 (a) and 8 (b) show quantum values for the input signal of the A / D converter depending on whether the resampling phase of the digital reproduced image signal output from the A / D converter is correct or not. FIG. 7 is a diagram showing a state where the activation range is changed. In the figure. 102,506: Clamp circuit 507: A / D converter 508: a variable delay circuit 103,509: phase control signal generating circuit 101: a variable gain amplifier S _1, S _2: Switch

Claims (1)

(57) [Claims] 1. A level control means for inputting an image signal, controlling the level of the input image signal and outputting the image signal, a clamp means for clamping and outputting the image signal output from the level control means, Converting means for converting an image signal output from the clamping means into a digital signal and outputting the digital signal; digital signal processing means for processing the digital signal output from the converting means; and a digital signal output from the converting means. An image signal processing device comprising: a control unit for controlling a level control characteristic of the level control unit and a clamp level control characteristic of the clamp unit.