JP3844486B2 - Image noise reduction circuit - Google Patents

Description

  The present invention relates to a video noise reduction circuit for reducing noise in a video signal in a video display device, a video recording / playback device, and the like.

JP-A-8-130664

FIG. 2 is a configuration diagram of a conventional image encoding device disclosed in Patent Document 1.
The image encoding apparatus stores an input image signal IN in a frame memory 35, which receives the input image signal IN frame by frame and rearranges the input image signal IN into block-unit image data, and the image data acquired in the block scan circuit 31 and the frame memory 35. A subtracting circuit 32 for calculating a difference value for each block of the image data of the previous frame subjected to the noise suppression process. A delay circuit 33 and an absolute value circuit 37 are connected to the output side of the subtraction circuit 32.

  The absolute value circuit 37 takes the absolute value of the difference value output from the subtraction circuit 32, and an accumulation circuit 38 for calculating the accumulated value of the absolute value for each block is connected to the output side. . On the output side of the accumulation circuit 38, a noise suppression determination circuit 39 that determines whether noise suppression processing is turned on or off by comparing the accumulated value with a threshold value, and a minimum accumulated value in one frame is detected and held. A minimum value detection circuit 40 is connected. Connected to the output side of the minimum value detection circuit 40 is a characteristic selection circuit 41 that determines a noise suppression characteristic according to the minimum accumulated value detected by the minimum value detection circuit 40. Output signals from the noise suppression determination circuit 39 and the characteristic selection circuit 41 are supplied to the noise suppression circuit 34.

  On the other hand, the delay circuit 33 adjusts the output timing of the difference value output from the subtraction circuit 32 and supplies it to the noise suppression circuit 34 in accordance with the timing of the output signals of the noise suppression determination circuit 39 and the characteristic selection circuit 41. . The noise suppression circuit 34 applies the block unit difference value provided from the delay circuit 33 based on the noise suppression processing on / off signal provided from the noise suppression determination circuit 39 and the noise suppression characteristic provided from the characteristic selection circuit 41. Noise suppression processing is performed. The output side of the noise suppression circuit 34 is connected to the addition circuit 35.

  The adder circuit 35 adds the difference value subjected to the noise suppression processing by the noise suppression circuit 34 and the image data of the previous frame stored in the frame memory 36 to thereby obtain the image data of the current frame subjected to the noise suppression processing. Is to be generated. The image data generated by the adder circuit 35 is stored in the frame memory 36, converted into a signal by the television scan circuit 42, and output as an output image signal OUT.

  In such an image encoding apparatus, one frame of the input image signal IN is divided into a plurality of block unit image data by the block scan circuit 31, and the noise suppression processing unit is subdivided. The block image data is subtracted from the image data subjected to noise suppression processing of the previous frame by the subtraction circuit 32, and the difference value is timing-adjusted by the delay circuit 33 and given to the noise suppression circuit 34.

  On the other hand, the absolute value of the difference value output from the subtraction circuit 32 is taken by the absolute value circuit 37, the accumulated value is calculated by the accumulation circuit 38, and given to the noise suppression determination circuit 39 and the minimum value detection circuit 40. . In the noise suppression determination circuit 39, the accumulated value for each block is compared with a threshold value, and a static region and a dynamic region are determined from the comparison result, and ON / OFF of the noise suppression processing is determined. That is, when the accumulated value is larger than the threshold value, it is determined as a moving region, and the noise suppression processing is turned off. On the other hand, when the accumulated value is smaller than the threshold value, it is determined as a still region, and the noise suppression processing is turned on. Further, the minimum value detection circuit 40 detects the minimum accumulated value, and the characteristic selection circuit 41 determines the noise suppression characteristic according to the detected minimum accumulation value.

  In the noise suppression circuit 34, noise suppression processing is performed on the difference value in units of blocks given from the delay circuit 33 based on the ON / OFF signal given from the noise suppression judgment circuit 39 and the noise suppression characteristics given from the characteristic selection circuit 41. Done. The difference value subjected to the noise suppression processing by the noise suppression circuit 34 is added to the image data of the previous frame stored in the frame memory 36 in the addition circuit 35 to generate image data of the current frame. The image data of the current frame generated by the adder circuit 35 is stored in the frame memory 36, converted into a signal by the television scan circuit 42, and output as an output image signal OUT.

  As described above, in this image encoding device, by performing the noise suppression processing of the input image signal IN in units of blocks, it is possible to reduce afterimages and blurs in the moving region and to perform noise suppression in the still region satisfactorily. It is supposed to be possible.

However, the conventional image coding apparatus has the following problems.
In other words, since noise is detected during the period of valid image data, motion components in the input signal and high frequency components due to jitter in the input signal are detected as noise, making it difficult to detect the amount of noise with high accuracy. Met.

  The present invention provides a video noise reduction circuit capable of detecting a noise amount with high accuracy and performing a good noise reduction.

  The video noise reduction circuit according to the present invention includes an image storage means for sequentially updating and storing the latest image data in units of one screen from the output video signal subjected to noise reduction processing, and storing the input video signal and the image storage means in the image storage means. A difference detection unit that detects a difference from the image data and outputs difference data; and a motion of the video between the input video signal and the image data stored in the image storage unit based on the difference data And a pulse generation means for detecting a timing at which no image component is present in the input video signal based on a synchronization signal corresponding to the input video signal and generating a timing pulse for noise amount detection Noise amount detecting means for detecting an average value of the noise amount from the difference data during a period when the timing pulse is given, and hysteresis by first and second thresholds. According to the characteristics, the first control signal for controlling the noise reduction operation is generated by comparing the average value of the noise amount detected by the noise amount detecting means with the first and second threshold values, and the third control signal. And noise reduction setting means for generating a second control signal for controlling the motion compensation operation based on the average value of the noise amount according to the hysteresis characteristic by the fourth threshold, and the difference data according to the first control signal. Correction data generation means for controlling on / off generation of correction data by turning on / off; and when motion of the image is detected by the motion detection means and a motion compensation operation is instructed by the second control signal In addition, the correction data generated by the correction data generation means is subjected to motion compensation to output the correction data subjected to motion compensation, and the motion of the video is not detected, or the second control When the motion compensation operation is prohibited by the signal, the motion compensation unit that outputs the correction data generated by the correction data generation unit as it is, and the input video signal is corrected by the correction data output from the motion compensation unit. Video correction means for outputting the output video signal.

  In the present invention, a pulse generating means for generating a timing pulse during a period in which no image component is present in the input video signal by the synchronization signal, and a noise amount detecting means for detecting the noise amount from the difference data based on the timing pulse, And noise reduction setting means for generating setting information for noise reduction based on the amount of noise. As a result, it is possible to accurately detect the amount of noise and to reduce noise satisfactorily without being affected by motion components and jitter in the input video signal.

  Furthermore, motion detection means for detecting motion of the video and motion compensation means for generating motion compensation data by performing motion compensation on the correction data generated by the correction data generation means are provided. Thereby, there is an effect that it is possible to perform motion compensation for noise reduction according to the amount of noise.

  The above and other objects and novel features of the present invention will become more fully apparent when the following description of the preferred embodiment is read in conjunction with the accompanying drawings. However, the drawings are for explanation only, and do not limit the scope of the present invention.

FIG. 1 is a configuration diagram of a video noise reduction circuit showing an embodiment of the present invention.
The video noise reduction circuit includes a difference detection unit (for example, a difference detection unit) 11, a video correction unit (for example, a subtraction unit) 12, a correction data generation unit (for example, a difference noise detection unit) 13, and an image storage unit (for example, An image storage unit) 14, a motion detection unit (for example, a motion detection unit) 15, and a motion compensation unit (for example, a motion compensation unit) 16 are included.

  The difference detection unit 11 detects a difference between the input video signal IN and the image data PIC of the previous frame subjected to the noise reduction process, and outputs difference data DEF. A differential noise detector 13 is connected to the output side of the difference detector 11.

  The differential noise detector 13 generates correction data COR for noise reduction from the differential data DEF based on a control signal CON and setting information SET described later.

  The motion detection unit 15 detects the motion of the image based on adjacent pixels of the difference data DEF output from the difference detection unit 11, and outputs a determination signal DET for the presence or absence of motion to the motion compensation unit 16. It has become.

  The motion compensation unit 16 is inserted between the differential noise detection unit 13 and the subtraction unit 12, and the correction data COR output from the differential noise detection unit 13 when the motion detection unit 15 determines that there is motion. When motion is detected, motion compensation is performed to reduce correction data. The motion compensation unit 16 outputs correction data COR2 after motion compensation and is supplied to the subtraction unit 12.

  The subtractor 12 subtracts the correction data COR2 generated by the motion compensator 16 from the input video signal IN to remove the noise component in the input video signal IN, and the output video subjected to noise reduction processing. The signal OUT is generated. The output video signal OUT for one frame generated by the subtracting unit 12 is stored in the image storage unit 14 as image data PIC.

  Further, this video noise reduction circuit has pulse generation means (for example, a pulse generation unit) 21 to which a synchronization signal SYN corresponding to the input video signal IN is given. The pulse generator 21 detects the timing of a vertical blanking period in which no image data exists from the synchronization signal SYN, and a timing pulse TP having a pulse width of a certain time (for example, one line) during the vertical blanking period. Is generated. On the output side of the pulse generator 21, noise amount detection means (for example, a maximum value detector 22 and an average value detector 23) is connected.

  The maximum value detection unit 22 detects the maximum value MX of the difference data DEF within the period in which the timing pulse TP is given. The average value detector 23 detects the average value AV of the difference data DEF within the period in which the timing pulse TP is given. Noise reduction setting means (for example, a detection condition setting unit 24 and a detection operation control unit 25) is connected to the output side of the maximum value detection unit 22 and the average value detection unit 23.

  The detection condition setting unit 24 calculates setting information SET for the differential noise detection unit 13 based on the maximum value MX of the difference data DEF detected by the maximum value detection unit 22. The setting information SET is used to set the input / output characteristics of the differential noise detection unit 13, and the slope of the noise detection line in the low level region of the differential data DEF, the noise upper limit line in the intermediate level region, and the noise convergence line in the high level region. It defines the inclination of

  On the other hand, the detection operation control unit 25 generates an on / off control signal CON for the differential noise detection unit 13 based on the average value AV of the differential data DEF detected by the average value detection unit 23. The control signal CON has a hysteresis characteristic. For example, the control signal CON is turned on when the average value AV exceeds the first threshold value TH1, and after that, even if the average value AV drops below the first threshold value TH1, the control signal CON is turned on. If the threshold value TH2 is equal to or greater than 2 (TH2 <TH1), the ON state is maintained. The control signal CON is turned off when the average value AV drops below the second threshold value TH2.

  The compensation operation control unit 26 generates an on / off control signal CON2 for the motion compensation unit 16 based on the average value AV of the difference data DEF detected by the average value detection unit 23. That is, the compensation operation control unit 26 operates the motion compensation unit 16 when the noise is moderate or lower, and stops the motion compensation unit 16 that reduces the correction data so that more noise can be reduced when the noise is high. A control signal CON2 is generated for this purpose.

  The control signal CON2 has a hysteresis characteristic, and is turned off when the average value AV of the difference data DEF exceeds the upper threshold value. After that, even if the average value AV drops below the upper threshold value, the control signal CON2 exceeds the lower threshold value. If so, the off state is maintained. The control signal CON2 is turned on when the average value AV drops below the lower threshold value. Further, the threshold value of the compensation operation control unit 26 is set to a value higher than the threshold value of the detection operation control unit 25.

  3A to 3D are explanatory diagrams of the operation of FIG. The operation of FIG. 1 will be described below with reference to FIG.

  As shown in FIG. 3A, when the synchronization signal SYN is input to the pulse generation unit 21, the vertical blanking period is detected by the pulse generation unit 21 and further corresponds to one line in the vertical blanking period. A timing pulse TP having a pulse width is generated. The generated timing pulse TP is given to the maximum value detection unit 22 and the average value detection unit 23.

  On the other hand, the difference detection unit 11 is supplied with the input video signal IN, and is read and supplied with the image data PIC of the previous frame subjected to the noise reduction processing stored in the image storage unit 14. As a result, the difference data DEF is output from the difference detector 11. As shown in FIG. 3D, the difference data DEF is composed of a difference due to the motion of the image between the previous and subsequent frames and a noise component superimposed on the input video signal IN. In general, the level of difference due to motion between frames is large, and the level of superimposed noise is a relatively small value. The differential data DEF is given to the maximum value detection unit 22 and the average value detection unit 23 together with the differential noise detection unit 13 and the motion detection unit 15.

  The motion detection unit 15 detects a motion based on the difference data DEF, and outputs a determination signal DET for the presence or absence of motion to the motion compensation unit 16.

  The maximum value detection unit 22 detects the maximum value MX of the difference data DEF during the period in which the timing pulse TP is given, and this detected maximum value MX is given to the detection condition setting unit 24. The detection condition setting unit 24 calculates setting information SET for the differential noise detection unit 13 based on the maximum value MX.

  The setting information SET is for setting the input / output characteristics of the differential noise detector 13 as shown in FIG. The setting information SET includes information that defines a noise detection line in the low level region of the difference data DEF, a noise upper limit line in the intermediate level region, and a noise convergence line in the high level region. As a result, the value of the difference data DEF input to the differential noise detector 13 is limited and output within the noise detection region surrounded by the noise detection line, the noise upper limit line, and the noise convergence line.

  Further, the average value detection unit 23 detects the average value AV of the difference data DEF in the period in which the timing pulse TP is given, and this average value AV is given to the detection operation control unit 25 and the compensation operation control unit 26. .

  The detection operation control unit 25 generates an on / off control signal CON for the differential noise detection unit 13 based on the given average value AV. The control signal CON has a hysteresis characteristic as shown in FIG. That is, when the control signal CON of the previous frame is on, the on state is maintained unless the average value AV of the current frame is equal to or lower than the threshold value TH2. When the control signal CON of the previous frame is off, the off state is maintained unless the average value AV of the current frame exceeds the threshold value TH1.

  The compensation operation control unit 26 generates an on / off control signal CON2 for the motion compensation unit 16 based on the average value AV of the difference data DEF. That is, the control signal CON2 is generated to operate the motion compensation unit 16 when the noise is moderate or lower, and to stop the motion compensation unit 16 when the noise is high.

  The setting information SET calculated by the detection condition setting unit 24 and the control signal CON generated by the detection operation control unit 25 are given to the differential noise detection unit 13 together with the difference data DEF output from the difference detection unit 11.

  In such a video noise reduction circuit, when the average value AV of the difference data DEF detected by the average value detection unit 23 is small, the control signal CON output from the detection operation control unit 25 is turned off, and the compensation operation control unit 26 The control signal CON2 output from is turned on. Thereby, the noise reduction process by the differential noise detection unit 13 is stopped, the correction data is not output, and the noise reduction process is stopped.

  When the average value AV of the difference data DEF is intermediate, both the control signal CON output from the detection operation control unit 25 and the control signal CON2 output from the compensation operation control unit 26 are turned on. As a result, the noise reduction processing by the differential noise detection unit 13 and the motion compensation processing are performed on the correction data by the motion compensation unit 16.

  When the average value AV of the difference data DEF is large, the control signal CON output from the detection operation control unit 25 is turned on, and the control signal CON2 output from the compensation operation control unit 26 is turned off. Thereby, the motion compensation process by the motion compensation unit 16 is stopped, and only the noise suppression process by the differential noise detection unit 13 is performed.

  As described above, this video noise reduction circuit includes the maximum value detection unit 22 and the average value detection unit 23 that detect the amount of noise from the input video signal IN that does not include an image component in the vertical blanking period. As a result, the amount of noise can be detected with high accuracy, and good noise reduction can be performed according to the amount of noise.

  In addition, when the noise is low, the control signal CON for stopping the operation of the differential noise detector 13 is output from the detection operation controller 23, so that afterimage and blur due to noise reduction processing are eliminated when the noise is low. There is an advantage that high image quality can be maintained.

  Furthermore, a compensation operation control unit 26 that performs on / off control of the operation of the motion compensation unit 16 according to the amount of noise is provided. As a result, there is an advantage that the noise reduction processing can be performed with the correction data that has been subjected to effective motion compensation according to the amount of noise.

In addition, this invention is not limited to the said embodiment, A various deformation | transformation is possible. Examples of this modification include the following.
(A) The function of differential noise detection in the differential noise detector 13 is not limited to that having the input / output characteristics as shown in FIG.
(B) The maximum value detection unit 22 detects the maximum value MX in the period of the timing pulse TP of one frame, but may detect the average of the maximum values of a plurality of consecutive frames in the past. good. As a result, image disturbance due to sudden noise can be prevented.
(C) The average value detection unit 23 detects the average value AV in the period of the timing pulse TP of one frame, but may detect the average of the average values of a plurality of consecutive frames in the past. good. As a result, image disturbance due to sudden noise can be prevented.
(D) The detection operation control unit 25 and the compensation operation control unit 26 have hysteresis characteristics. However, in order to simplify the circuit, the detection operation control unit 25 and the compensation operation control unit 26 may be configured with a simple comparison circuit.
(E) The pulse generator 21 detects a vertical blanking period from the synchronization signal SYN, generates a timing pulse TP having a pulse width corresponding to one line in the vertical blanking period, and generates noise detection timing. However, data signals and the like may be multiplexed during the vertical blanking period. In such a case, erroneous detection can be avoided by using a circuit that determines whether the noise amount of the color difference signal is correct by referring to the noise amount in the luminance signal in the input video data IN.
(F) The detection condition setting unit 24 calculates the setting information SET for the differential noise detection unit 13 on the basis of the maximum value MX detected by the maximum value detection unit 22, but the level is set to the maximum value MX. Based on the plurality of predetermined setting information, the setting information SET for the differential noise detection unit 13 may be selected.
(G) Noise reduction processing is performed in units of one frame of the input video signal IN. However, in the case of an interlace method in which one frame is composed of two fields, noise reduction processing may be performed in units of one field. good.
(H) The motion compensation unit 16 performs on / off control of the operation by the control signal CON2 given from the compensation operation control unit 26. When the control signal CON2 is turned off, the motion compensation process is stopped. Alternatively, the processing level may be lowered.
(I) The on / off control of the operations of the differential noise detection unit 13 and the motion compensation unit 16 is performed according to the average value AV of noise. The average value AV of noise is further divided into a plurality of levels. Then, noise reduction processing and motion compensation processing corresponding to each level may be performed.

It is a block diagram of the video noise reduction circuit which shows the Example of this invention. It is a block diagram of the conventional image coding apparatus. It is operation | movement explanatory drawing of FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 Difference detection part 12 Subtraction part 13 Differential noise detection part 14 Image memory | storage part 15 Motion detection part 16 Motion compensation part 21 Pulse generation part 22 Maximum value detection part 23 Average value detection part 24 Detection condition setting part 25 Detection operation control part 26 Compensation Operation control unit

Claims (1)

Image storage means for sequentially updating and storing the latest image data for each screen from the output video signal subjected to noise reduction processing;
Difference detection means for detecting a difference between the input video signal and the image data stored in the image storage means and outputting difference data;
Motion detection means for detecting a motion of the video between the input video signal and the image data stored in the image storage means based on the difference data;
Pulse generation means for detecting a timing at which no image component is present in the input video signal based on a synchronization signal corresponding to the input video signal, and generating a timing pulse for noise amount detection;
A noise amount detecting means for detecting an average value of the noise amount from the difference data during a period when the timing pulse is given;
According to a hysteresis characteristic by the first and second threshold values, a first noise level control operation is controlled by comparing an average value of the noise amounts detected by the noise amount detecting means with these first and second threshold values. Noise reduction setting means for generating a control signal and generating a second control signal for controlling a motion compensation operation based on an average value of the noise amount according to hysteresis characteristics by the third and fourth thresholds;
Correction data generation means for performing on / off control of generation of correction data by turning on / off the difference data in accordance with the first control signal;
When motion of the image is detected by the motion detection means and a motion compensation operation is instructed by the second control signal, motion compensation is performed by applying motion compensation to the correction data generated by the correction data generation means. Motion compensation that outputs the correction data performed and outputs the correction data generated by the correction data generation means as it is when the motion of the video is not detected or the motion compensation operation is prohibited by the second control signal Means,
Video correction means for correcting the input video signal with correction data output from the motion compensation means and outputting the output video signal;
A video noise reduction circuit comprising:

Images