CA1218145A

CA1218145A - Circuit arrangement for removing noise of a color video signal

Info

Publication number: CA1218145A
Application number: CA000457247A
Authority: CA
Inventors: Takashi Kuriyama; Shintaro Nakagaki
Original assignee: Victor Company of Japan Ltd
Current assignee: Victor Company of Japan Ltd
Priority date: 1983-06-24
Filing date: 1984-06-22
Publication date: 1987-02-17
Also published as: JPS605692A; US4630104A; KR850000861A; BR8403133A; EP0132310A1; DE3471420D1; KR870001836B1; EP0132310B1

Abstract

TITLE OF THE INVENTION
CIRCUIT ARRANGEMENT FOR REMOVING NOISE
OF A COLOR VIDEO SIGNAL
ABSTRACT OF THE DISCLOSURE
A luminance signal and a chroma signal of a color video signal are processed respectively such that first and second signals are generated, where the first signal indicates the contour line of images represented by the video signal and the second signal includes noise included in the chroma signal and a signal component having an amplitude substantially equal to the peak to peak value of the noise. These first and second signals are then fed to either a switching circuit or a multiplier so that a resultant output signal having only the noise is obtained. The noise components are then subtracted, by way of a subtracted, from the chroma signal so that a chroma signal having no noise will be obtained.

Description

~.%~81~5 TITLE OF THE INVENTION
CIRCUIT ARRANGEMENT FOR ROOMING NOISE
OF A COLOR VIDEO SIGNAL
BACKGROUND OF THE INVENTION

This invention relates generally to video signal processing, and more particularly to a circuit arrangement.
for removing noise included in a color video signal thereby improving signal-to-noise ratio of the video signal for obtaining a high-quality reproduced picture.
It is naturally required that a video signal of satisfactory signal-to-noise ratio (S/N) is provided for obtaining a reproduced image of high quality, and various apparatus for processing a video signal have hitherto been proposed for obtaining a video signal of satisfactory S/N.
In a conventional circuit arrangement for improving S/N of a Video signal, such as a chrome signal from a pickup tube of a video camera, noise include in the video signal is reduced by subtracting a noise signal, which is produced by extracting noise components of the video signal 20 from the video signal, from the video signal. In tins way, since noise reduction has hitherto been effected by simply subtracting the noise components from the video signal, where the noise components are produced by way of a differentiator responsive to the video signal and a clipping circuit responsive to an output signal from tune

- 2 - I

differentiator, a resultant video signal obtained as the result of subtraction has suffered from dull or blunt leading and trailing edges in the waveform where luminance drastically changes. Accordingly, the resultant video signal obtained in this way has a waveform different from that of the output signal from the video camera especially at portions corresponding to contour of images taken.
because of such deteriorated waveform of the video signal white balance of the video signal is disturbed resulting in a phenomenon wherein a picture obtained by reproducing the video signal suffers from the occurrence of colored border at the contour lines of subjects taken.
S MARY OF THE INVENTION
The present invention has been developed in order to remove the above-descrlbed drawbacks inherent to the conventional circuit arrangement for improving S/N of a video signal.
It is, therefore, an object of the present invention to provide a new and useful circuit arrangement for improving S/N of a video signal by effectively removing or reducing noise included in the video signal so that the waveform of the processed video signal does not suffer from dull or blunt ladling or trailing edges.
According to a feature of the present invention a luminance signal and a chrome signal of a color video signal are processed respectively such that first and second signals are generated, where the first signal indicates the contour line of images represented by the video signal and the second signal includes noise included in the chrome signal and a signal component having an amplitude substantially equal to the peak to peak value of the noise. These first and second signals are then fed to either a switching circuit or a multiplier so that a resultant output signal having only the noise is obtained.
The noise components are then subtracted, my way of a subtracter, from the chrome signal so that a chrome signal having no noise will be obtained.
In accordance with the present invention there is provided a circuit arrangement for removing noise included in a color video signal including a luminance signal and a shim signal, comprising: first means responsive to said luminance signal of said video signal for generating a first signal indicative of the contour lines of images of a picture which is represented by said video signal; second means responsive to said chrome signal of said video signal for generating a second signal including noise of said chrome signal, and a signal component having an amplitude substantially equal to that of the peak to peak value of said noise; a switching circuit responsive to said first and second signals and having a do voltage source so that switching between said second signal and a do voltage from said do voltage source is effected in response to said first signal for producing a third signal including only said noise of said second signal; and a subtracter responsive to sail chrome signal and said third signal for producing an output color video signal indicative of the difference between said chrome signal and said noise of said third signal.
In accordance with the present invention there is also provided a circuit arrangement for removing noise included in a color video signal including a luminance signal and a chrome signal, comprising: first means responsive to said luminance signal of said video signal for generating a first signal indicative of the contour lines of images of a picture which is represented by said video signal; second means responsive to said chrome signal of said video signal for generating a second signal including noise of said chrome signal, and a signal component having an amplitude substantially equal to the peak to peak value of said noise; a multiplier responsive to said first and second signals so that said first signal is multiplied my said second signal for producing a third signal including only said noise of said second signal; and a subt~actor responsive to said chrome signal and said third signal or producing an output color video signal _ 5 3-~5 indicative of the difference between said chrome signal and said noise of said third signal.
BRIEF DESCRIPTION OF THE DRAWINGS
The object and features of the present invention will now become more readily apparent from the fuliginous detailed description of the preferred embodiments taken in conjunction with the accompanying drawings in which:
Fig. 1 is a block diagram showing a conventional circuit arrangement;
Fig. 2 is a block diagram showing another conventional circuit arrangement;
Fig. 3 is a schematic block diagram showing an embodiment of the circuit arrangement according to the present invention;
Fig. 4 is a schematic block diagram showing a portion of another embodiment of the circuit arrangement according to the present invention;
Fig. 5 is a circuit diagram of the polarity uniforming circuit of Figs. 3 and 4;
Fig. 6 is a circuit diagram of the multiplier of Fig. 3;
Fig. 7 is a circuit diagram of another multiplier which may be used in place of the multiplier of Fig. 6; and Fig. 8 is a schematic block diagram showing a circuit arrangement for a video camera to which circuit arrangement is applied the present invention.
The same or corresponding elements and parts are designated at like reference numerals throughout the drawings DETAILED DESCRIPTION OF THE INVENTION
Prior to describing the preferred embodiments of the present invention, the above-mentioned conventional circuit arrangements will be described for a better under-standing of the present invention. Figs. 1 and 2 are block diagrams showing examples of circuit arrangement for pro-cussing a video signal, which have been conventionally used for improving S/N of a color video signal, and in Figs. 1 and 2, the reference 1 is an input terminal of a color video signal; 2, a differentiator; pa and 3b, clipping circuits;
I, a subtracter; 5, an output terminal; 6, a low pass filter; and 17, an adder.
In the conventional circuit arrangement shown in Figs, 1 and 2, when a color video signal including noise "n" as seen in waveform C of respective diagrams, it applied to the input terminal 1, the color video signal C
is then fed to the differentiator 2 and the subtracter 4 in the conventional arrangement Go Fig. 1, and to the diferentiator 2 and the low pass filter 6 in the conventional arrangement of Fix. I
High frequency components Oh of the color video signal C are outputted from the differentiator 2 wit the color video signal being differentiated by the differentiator 2. The output signal Oh from the above-mentioned differentiator 2 is clipped at a signal level corresponding to peak to peak value of the noise by the clipping circuit pa, 3b so that signal Shea, Cub of the drawing is outputted from the clipping circuit pa, 3b.
In the conventional circuit arrangement of Fig 1, the above-mentioned output signal Shea from the clipping circuit pa is supplied to the subtracter 4 as a subtrahend signal so as to be subtracted from the input color video signal C applied to the subtracter 4 as a minuend signal, and therefore an output color video signal Cot is outputted from the subtracter 4 to the output terminal 5. In the conventional circuit arrangement of Fig 2, the above-mentioned output signal Chub from the clipping circuit pa and an output signal from the low pass filter 6 are added to each other by the adder 17 so that an output color video signal Coy is outputted from the adder 17 to the output terminal 5.
In the conventional circuit arrangement described with reference to Figs. 1 and 2, the output color video signal Cot, Coy outputted to the output terminal 5 has a waveform different from that of the input color video signal at its rising portion and falling portion, and s therefore, white balance is lost at the contour portion of a reproduced image resulting in the occurrence of a colored border.
Referring now to Fig. 3, an embodiment of the circuit arrangement according to the present invention is shown. In Fig. 3 r the references 18 and 10 are input terminals for a luminance signal Y and a chrome signal derived from a color video signal video signals; 7 and 11, differentiators; 8j a polarity-uniforming circuit; 9 and 12, clipping circuits; 13, a multiplier (gate circuit for multiplication); 14 and 15, subt~act~rs.; 16, an output terminal.
The above-mentioned differentiator 7, the polarity-uniforming circuit 8, the clipping circuit 9 form a first signal generating circuit Sol for producing a contour line signal, and the first signal generating circuit Sol outputs a contour line signal Yip in correspondence with a portion where luminance variation is large in the luminance signal Y fed to the input terminal 18 of the video signal, and the contour line signal is fed to a noise extracting circuit NPC in turn.
Namely, the luminance signal Y fed to the input terminal 18 in Fig. 3, is outputted as a signal Ye from the differentiator 7 after being differentiated by the differentiator 7, and subsequently the output signal Ye from the differentiator 7 is fed to the clipping circuit 9 with its polarity being made uniform by the polarity-uniforming circuit 8 a a signal Ye' in Fig. 3, The clipping circuit 9 clips the signal Ye' fed thereto at an appropriate level so as to produce the contour line signal Yip which is fed to an input terminal "a" of a multiplier 13 pa gate circuit 13 for multiplication) of the noise extracting circuit NPC.
While the above-mentioned first signal generating circuit Sol chutney in Fig. 3 is constructed of the differentiator 7, the polarity-uniforming circuit 8, the clipping circuit 9, Fig. 4 is a block diagram showing another structural example of the first signal generating circuit SO In this another first signal generating circuit Sol of Fig. 4, a delay circuit pa and a su~tractor 7b are used in place of the differentiator 7 chutney in Fig.

3 so that the contour line signal is obtained using the luminance signal Y and a delayed signal Ye of the luminance signal Y.
Fig. 5 shows an example of the po]arity-uniforming circuit 8 show in Figs. 3 and 4. As will be understood from the circuit diagram a transistor Al responsive to the signal Ye from the differentiator 7 of Fig. 3 or from the subtracter 7b of Fig. 4 develops an opposite polarity output signal at its collector, while another transistor Q2 - 1 o - 5 develops an output sign l of the same polarity as thaw of the signal Ye at its collector. These two signals are respectively inverted by transistors Q3 and Q4, and then portions whose voltage is higher than a reference voltage En prom a voltage source are respectively detected by transistors Q5 and Q6, and are extracted to be added to each other ho a resistor Row Then an output signal Ye' having only positive polarity is obtained at an Olltpvt terminal.
lo The chrome signal C fed to the input terminal lo in Fig. 3, is differentiated by a differentiator 11 of the second signal generating circulate SG2 also having a clipping circuit 12. As a result, a signal Oh including high frequency components and a signal component having lo substantially the same amplitude as peak Jo peak value of noise components included in the high frequency components is obtained. Then the signal Oh is clipped by the clipping circuit 12 so that an output signal Oh' including noise of the chrome signal and the signal component having an amplitude substantially equal to that of the peak to peak value of said noise us ohta~ned.
As the above-mentioned clipping circuit 12 may be used a circuit having a structure so that it is possible to clip the signal Oh in connection with both positive and negative sides at a signal substantially the same as the peak to peak value of the noise "n" included in the sisal Oh fed thereto, and a slicer may also be used as the above-mentioned clipping circuit 12.
The above-described first and second signal generators SG1 and SG2 are both described in applicant's prior patents titled "Noise Reduction Circuit fur a Color Video Signal" (Japanese provisional publication No, 5~-1864~3 published October 23, 1~84; US provisional publication No. 2,141,6Q3 published December I 84) lo and corresponding to Canadian Patent No. 1,202,410 patented March 25, 1986~
The signal Oh' outptltted from the second signal generating circuit SG2 is fed to an input terminal "b" of the multiplier (gaze circuit fox multiplication 13 of the noise extracting circuit NPC, and is Also fed to the subtracter 14 of the noise extracting circuit NPC as a minuend signal. As the abo~e-mentioned multiplier 13 may be used as a circuit arrangement having a structure shown in Fig. 6 or instance, The multiplier 13 effects multiplication between the output signal Yip (contour signal Ypl fed from the first signal generating circuit Sol to the input terminal "a"
thereof and the output signal Oh' fed from the second signal generating circuit 5G? to the input terminal "b"
2$ thereof, so as to output a sl~nal Oh" illustrated in Fig. 3 from an output terminal "c"
The output signal Oh" from the multiplier 13 is supplied as a subtrahend to the subtracter 14, to which the signal Oh' is fed as a minuend signal And then the subtracter 14 of the noise extracting circuit NPC outputs a signal having no signal components jut only noise as shown at On in Fig. 3, While in the noise extracting circuit NPC of thy embodiment circuit arrangement of Fig. 3, the output signal Oh" from the multiplier 13 is subtracted from the output signal Oh' from the second signal generating circuit SG2 so as to obtain the signal On of Fig 3, having no signal components but only noise, in a multiplier 13 having a structure a shown in Fig. 6 it is also possible to directly output the signal On having no signal components but only noise from the output terminal "c" Go the multiplier 13 by setting a do voltage to a peak voltage of the signal Ye whereon the do voltage is fed from a do voltage source En used for setting deco balance. Therefore, when practicing the present invention, the noise extracting circuit NPC may be constructed of only the multiplies 13 having the structure of Fig. 6, and in this case, the subtracter 14 of Fig. 3 can be omitted when constructing the circuit arrangement. On the other hand, when the do voltage is set to a peak voltage of the signal Yip, then the multiplier 13 produces the output signal Oh" as described in the above, and therefore, the subtracter 14 is necessary for obtaining the signal on hiving only noise components.
The signal On having no signal components but only noise, i.e. the output signal On from the above-mentioned noise extracting circuit NPC, is fed to the subtracter 15 as a subtrahend signal. In the subtracter 15, the output signal On from the above-mentioned noise extracting circuit NPC is subtracted from the chrome signal C fed from the input terminal 10 of video signal as a minuend signal for outputting an output signal Co to an output terminal 16.
Since the output signal Co sent from the sub~ractor 15 to the output terminal 16 in the above-described manner has no deterioration ion pulse characteristic, the above-mentioned problem inherent to the conventional examples can be satisfactorily resolved by the circuit arrangement according to the present invention.
Fig. 7 shows a circuit diagram of a switching circuit which may be used in place of the multiplier 13 of Figs. 3 and 6. this switching circuit of Fig. 7 is a grating circuit performing switching between the signal Oh' fed from the second signal generating circuit SG2 to a transistor Q7 and a do voltage fed from a do voltage source Al fed to a transistor Q8. The contour line signal Yip from the first signal generating circuit Sol is fed to a transistor Ill as a grating signal, while a reference do voltage is fed from a reference voltage source V2 to a transistor Ql2. The transistor Ill is rendered conductive and the transistor Ql2 is rendered nonconductive when the voltage of the contour line signal Yip is greater than the reference voltage V2. As a result, current flows via the transistors Q7 and Q9 so that the input signal Oh' is outputted as an output signal Volt. On the other hand, when the voltage of the contour line signal Yip is equal to or less than the reference voltage V2, the transistor Ill becomes nonconductive while the transistor Q12 becomes conductive. As a result, current flows via the transistors Q8 and Q10, and therefore, the output voltage Volt is fixed at the do voltage Al. With this operation t the switching circuit produces the output voltage ah" of Fig. 3.
As shown in Fig. 7, when an inventor 50 shown by way of dotted lines is used for inverting thy contour line signal Yip before supplying the same to the transistor Ill, then the switching circuit produces the signal On shown in Fig. 3. Accordingly, the subtracter 14 is not needed when the inventor 50 is employed.
Fig. 8 is a block diagram showing a case in which the circuit arrangement for processing video signal according to the present invention is applied to a single-tube color television camera to which step energy demodulation system is applied. In Fly. 8, the reference 20 is a subject to be imaged; 21, a lens; 22, a pickup tube;
I a deflection yoke; 24, photoelectric converting portion;
F, a color-separatlon stripe filter; 25, a front panel of the pickup tube; LPFw and LPFn, low pass filters; BPFl and BPF2, band pass filters; DUD, a demodulator; Dell and DWIGHT, detectors; and MIX, a matrixing circuit.
In Fig. I, Sol corresponds to the first signal generating circuit indicated at the reference Sol in Fig.
3, while Sty SG2r, SG2b and so on in Fig. 6 respectively correspond to the second signal generating circuit SG2 indicated at the reference SG2 in Fig. 3. Furthermore, NPCy, NPCr, NPCb and so on of Fig. 6 respectively correspond to the noise extracting circuit NPC indicated at the reference NPC in Fog. 3. Similarly J yo-yo, or 15b and so on of Fig 6 respectively correspond to the subtracter 15 indicated at the reference 15 in Fig. 3.
In the color television camera shown in Fig. 6, to the first signal generating circuit Sol for generatillg a contour signal is supplied a luminance signal obtained from the output stage of the low pass filter LPFn, and the contour signal generated by the first signal generating circuit Sol is fed to the noise extracting circuits NPCy, NPCr and NPCb so that the luminance signal and the chrome signal, whose noise has teen removed or reduced while pulse characteristic is satisfactory, are fed to the matrixing circuit MIX. As a result, three primary color signals of high quality can be obtained from the matrixing circuit MIX. It is a matter of course that the circuit arrangement for processing video signal according to the present invention can be applied for removing or reducing noise of color difference signals yin the same manner as in the case of the above mentioned primary color signals.
As is apparent from the above detailed description, since a signal including only noise is produced from a video signal, and the signal including only noise is subtracted from an original signal so that a signal whose noise has been removed or reduced is obtained in the circuit arrangement according to the present invention, the output signal from the circuit arrangement has a satisfactory pulse characteristic, and therefore it is apparent that the problem inherent to the conventional example circuit arrangement can be obviated according to the circuit arrangement for processing a video signal according to the present invention.
The above-described embodiments are just examples of the present invention, and therefore, it will be apparent for those skilled in the art that many modifications and variations may be made without departing prom the spirit of the present invention.

Claims

WHAT IS CLAIMED IS:

1. A circuit arrangement for removing noise included in a color video signal including a luminance signal and a chroma signal, comprising:
(a) first means responsive to said luminance signal of said video signal for generating a first signal indicative of the contour lines of images of a picture which is represented by said video signal;
(b) second means responsive to said chroma signal of said video signal for generating a second signal including noise of said chroma signal, and a signal component having an amplitude substantially equal to the peak to peak value of said noise of said chroma signal;
(c) a switching circuit responsive to said first and second signals and having a d.c. voltage source so that switching between said second signal and a d.c. voltage from said d.c. voltage source is effected in response to said first signal for producing a third signal including only said noise of said second signal; and (d) a subtractor responsive to said chroma signal and said third signal for producing an output color video signal indicative of the difference between said chroma signal and said noise of said third signal.

2. A circuit arrangement as claimed in Claim 1, wherein said first means comprises:
(a) a differentiator responsive to said luminance signal;
(b) a polarity uniforming circuit responsive to an output signal from said differentiator so that differetial pulses of positive and negative polarities included therein are uniformed to either positive or negative polarity; and (c) a clipping circuit responsive to an output signal from said polarity uniforming circuit for producing said first signal.

3. A circuit arrangement as claimed in Claim 1, wherein said first means comprises:
(a) a delay circuit responsive to said luminance signal for retarding said luminance signal by a predetermined period of time;
(b) a subtractor responsive to said luminance signal and an output signal from said delay circuit for producing a difference signal therebetween;
(c) a polarity uniforming circuit responsive to said difference signal so that pulses of positive and negative polarities included therein are uniformed to either positive or negative polarity; and (d) a clipping circuit responsive to an output signal from said polarity uniforming circuit for producing said first signal.

4. A circuit arrangement as claimed in Claim 1, wherein said second means comprises:
(a) a differentiator responsive to said chroma signal;
and (b) a clipping circuit responsive to an output signal from said differentiator for producing said second signal.

5. A circuit arrangement as claimed in Claim l, wherein said d.c. voltage of said d.c. voltage source is set to a peak voltage of said first signal.

6. A circuit arrangement for removing noise included in a color video signal including a luminance signal and a chroma signal, comprising:
(a) first means responsive to said luminance signal of said video signal for generating a first signal indicative of the contour lines of images of a picture which is represented by said video signal;
(b) second means responsive to said chroma signal of said video signal for generating a second signal including noise of saId chroma signal, and a signal component having an amplitude substantially equal to the peak to peak value of said noise;
(c) a multiplier responsive to said first and second signals so that said first signal is multiplied by said second signal for producing a third signal including only said noise of said second signal; and (d) a subtractor responsive to said chroma signal and said third signal for producing an output color video signal indicative of the difference between said chroma signal and said noise of said third signal.

7. A circuit arrangement as claimed in Claim 6, wherein said first means comprises.
(a) a differentiator responsive to said luminance signal;
(b) a polarity uniforming circuit responsive to an output signal from said differentiator so that differential pulses of positive and negative polarities included therein are uniformed to either positive or negative polarity; and (c) a clipping circuit responsive to an output signal from said polarity uniforming circuit for producing said first signal.

8. A circuit arrangement as claimed in claim 6, wherein said first means comprises:

(a) a delay circuit responsive to said luminance signal for retarding said luminance signal by a predetermined period of time;
(b) a subtractor responsive to said luminance signal and an output signal from said delay circuit for producing a difference signal therebetween;
(c) a polarity uniforming circuit responsive to said difference signal so that pulses of positive and negative polarities included therein are uniformed to either positive or negative polarity; and (d) a clipping circuit responsive to an output signal from said polarity uniforming circuit for producing said first signal.

9. A circuit arrangement as claimed in Claim 6, wherein said second means comprises:
(a) a differentiator responsive to said chroma signal;
and (b) a clipping circuit responsive to an output signal from said differentiator for producing said second signal.

10. A circuit arrangement as claimed in Claim 6, wherein said multiplier comprises a d.c. voltage source for providing a d.c. voltage used for d.c. voltage balancing, said d.c. voltage being set to a peak voltage of said first signal.

11. A circuit arrangement as claimed in Claim 6, further comprising a subtractor responsive to said second signal and to an output signal from said multiplier for producing a difference signal therebetween which corresponds to said third signal; said multiplier comprising a d.c. voltage source for providing a d.c. voltage used for d.c. voltage balancing, said d.c. voltage being set to a base line voltage of said first signal.