CN1175855A - Method and apparatus for compensating quantization errors of decoded video signal by using adaptive filter - Google Patents
Method and apparatus for compensating quantization errors of decoded video signal by using adaptive filter Download PDFInfo
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Abstract
The Huffman decoding and re-quantization technology is used to convert the coding video signal into a group of DCT coefficients corresponding to the present frame data. The spatial characteristics of the present frame data is confirmed according to the decoded previous frame data before obtaining the present frame data so as to filter the high-frequency constituent of the DCT coefficients. Then the filtered coefficients are converted into a group of reverse DCT data. The group of data and the previous frame data are used to produce the present frame data through motion compensation and the present frame data are used as the new previous frame data and for decoding the video signal.
Description
The invention relates to the method and apparatus that is used for the decoding video signal that is encoded, more specifically say so about can by according to the standard deviation of the pixel value of a plurality of previous frames of before deriving current frame data, decoding adaptively the high frequency composition of filtering current frame data compensate the method and apparatus of the quantization error of decoded video signal.
In the digital television system of for example visual telephone, video conference and high definition television system, need a large amount of numerical datas to define each frame of video signal, because the video line signal in the vision signal includes a series of numerical data that is known as pixel value.But because the limited bandwidth that common transmission channel can be used, in order to pass through its a large amount of numerical datas of transmission, to adopt various digital compression technologies to compress inevitably or promptly reduce data volume, particularly under the situation of the video coder that resembles the such low bit rate of video telephone and video conference system.
The normal condition vision signal can be compressed and unlikely its integrality that has a strong impact on, because always exist certain correlation promptly redundant usually in some pixels in a frame and in the middle of the pixel at consecutive frame.In various video compression technologies, the so-called mixed coding technology that time and space compression compress technique statistical coding technology are combined be known as the most effective.
Between most of mixed coding technology employing adaptive frame/and the frame mode coding, orthogonal transform, quantization of transform coefficients, and Variable Length Code (VLC).Between adaptive frame/frame mode coding is a pulse-code modulation by present frame (PCM) data or by differential pulse code modulation (DPCM) data, for example according to their variance, selects to be used to do the process of the vision signal of orthogonal transform subsequently adaptively.Coded in inter mode also is referred to as predicted method, be based on this idea of redundancy that reduces consecutive frame, it is the definite motion of a target between present frame and its one or two consecutive frame, according to the motion of this target stream and prediction present frame, and generate a process of representing the differential signal of the difference between this present frame and its prediction.This coding method is at " the fixing and adaptive predictor that is used for hybrid predicting/transition coding " (IEEE-Transactions on Communicatians of for example Staffan Exicssn, COM-33, No.12, (in December, 1985)) and " the motion compensation interframe encoding scheme of TV image " (IEEETransactions on Communications of Ninomiya and Ohtsuka, COM-30, No.1, (January nineteen eighty-two)) in have disclosedly, this two literary composition is referred to herein as a reference.
Spatial coherence between the pictorial data of orthogonal transform utilization as the DPCM data of the PCM data of present frame and motion compensation reduces or removes spatial redundancy between them, and it is used to the piece of a digital image data is transformed into one group of conversion coefficient.This technology was introduced in " scene adaptive coding device " (IEEE Transactions on Communications, COM-32, No.3, (in March, 1984)) of Chen and Pratt.By handling this transform coefficient data with quantification and VLC, the data volume that be transmitted can effectively be compressed.
Specifically, in the orthogonal transform as discrete cosine transform (DCT) etc., pictorial data is divided into the data block of equal sizes, the data block of 8 * 8 pixels for example, and each data block is become frequency domain by space field transformation.Average pixel density in the DC coefficient reflection data block of piece.Usually, pixel in the frame mode incoming video signal has by the value in 0 to 255 scope, and obtain piece DC conversion coefficient in this frame by 0 to 2040 (can 11 bits represent) dynamic range and to the pact-1000 of piece AC conversion coefficient in the arbitrary frame maximum dynamic range to 1000.In the pixel value of inter-frame mode incoming video signal is-255 to 255 situation, the maximum dynamic range of any AC or DC conversion coefficient is about-2000 to 2000.
To be quantized by the orthogonal transform coefficient that orthogonal transform obtains then.When quantizing, obvious one less quantiser step size can bring the relatively large data of code bit that are used for representing it that require larger amt, and the result of a relatively largeization device step-length then is the data that its code bit is represented in less being used for of more a spot of need.And the fewer code bit of code potential energy of larger amt shows an image more accurately.Thereby in data volume or be added between burden that transmits on the passage and the quality that is transmitted image and will have one to trade off.
Various quantization step controlling schemes are arranged.In these schemes, quantiser step size control usually means the control to step-length used in the quantification of carrying out piece AC coefficient in interframe block AC and DC and the frame.The control of such quantiser step size is stored in data volume in the buffer storage and the complexity of incoming video signal is determined by current.At interframe block AC and DC, and in the frame under the situation of piece DC coefficient, for example 16 or 8 quantize with relatively little fixed step size, as disclosing in the Moving Picture Experts Group-2; And in frame under the situation of piece AC coefficient, the quantiser step size of upper frequency is greater than the quantiser step size of lower frequency.
Block effect is that a kind of edge of data block becomes visible phenomenon at receiving terminal.This block effect be because the frame fact of encoding by the data block unit; And bigger at quantiser step size, that is data block may be even more serious when standing more coarse quantification.Thereby in frame in the piece AC coefficient, because the quantiser step size of upper frequency is greater than the quantiser step size of lower frequency, it is more obvious that one given luminance difference with its adjacent block becomes, and causes more serious block effect and reduction image quality thus.Even in the situation with movement compensating frame prediction coded in inter mode, though block effect may be unobvious like this, it still can be in sight.
Therefore, main purpose of the present invention just provide a kind of by according to the standard deviation of the pixel value of a plurality of previous frames of before deriving current frame data, decoding adaptively the high fdrequency component of filtering current frame data compensate the vision signal coding/decoding method and the equipment of the quantization error of decoded video signal.
According to one aspect of the present invention, provide a kind of being used for to produce the method for decoded video signal by encoded video signal is decoded, wherein decoded signal packet contains a plurality of frames, and this method comprises step: (a) employing variable-length decoding processing encoded video signal draws one group of discrete cosine transform coefficient that is quantized corresponding to present frame thus; (b) this group quantized-dct transformation of coefficient is become one group of discrete cosine transform coefficient; (c) detect the spatial character of current frame data according to the frame data of before obtaining current frame data, decoding; (d) according to the high frequency composition of this group discrete cosine transform coefficient in spatial character filtering one presumptive area of this group discrete cosine transform coefficient and current frame data, produce one group of discrete cosine transform coefficient thus through filtering; (e) discrete cosine transform coefficient that will organize through filtering is for conversion into one group of inverse discrete cosine transform data; (f) generate current frame data according to these group inverse discrete cosine transform data and frame data by utilizing motion compensation; (g) with current frame data as decoded video data.
According to another aspect of the present invention, provide a kind of being used for to produce the equipment of decode video data by coding video frequency data is decoded, wherein decoded video signal comprises a plurality of frames, and this equipment comprises: frame memory is used to leave in the data that obtain the previous frame of decoding before the current frame data; Variable length decoder is used to utilize variable-length decoding to handle coding video frequency data, draws one group of discrete cosine variable coefficient through quantizing thus; Inverse quantizer is used for that this group is quantized the discrete cosine system change and becomes one group of discrete cosine transform coefficient; Filter is used for according to the data of this group discrete cosine transform coefficient and previous frame this group discrete cosine transform coefficient high frequency composition in one presumptive area being shielded, and produces one group of discrete cosine transform coefficient through filtering thus; Inverse discrete cosine transformer, the discrete cosine transform coefficient that is used for will organizing through filtering is transformed to one group of inverse discrete cosine transform data, motion compensator is used for generating current frame data based on these group inverse discrete cosine transform data and frame data by utilizing motion compensation; And feeder, be used for current frame data being delivered to frame memory as a new frame data and current frame data being provided as the vision signal through decoding.
Above-mentioned and other purposes of the present invention and characteristics will be by will be very clear to the preferred embodiment illustration below in conjunction with accompanying drawing, in the accompanying drawing:
Fig. 1 illustrates the block diagram that is used to produce the vision signal decoding device of decoded video signal according to of the present invention;
Fig. 2 is the more detailed block diagram of the sef-adapting filter 150 among Fig. 1; With
Fig. 3 represents the filtering interval according to 8 * 8 pixel blocks of the present invention.
Referring to Fig. 1, shown in block diagram be vision signal decoding device 100 according to the generation decoded video signal of the preferred embodiments of the present invention.
As can seeing among Fig. 1, be coupled to buffer 110 in the decoding device 100 from the bit stream that is encoded of corresponding conventional coders (not shown).Buffer 110 receives this bitstream encoded and it is offered a demultplexer (DEMUX) 120 with a fixed rate, make Signal Separation to produce the decoded information signal at this bit stream that will be encoded, one interframe/frame mode signal for example, quantization step, with the pictorial data that is encoded, that is the motion vector of the conversion coefficient of one group of Variable Length Code and coding.Interframe/frame mode signal is coupled to inverse quantizer 140 and adder 180 by line L12; Quantization step offers inverse quantizer 140 by line L10; And the conversion coefficient of this group Variable Length Code and the motion vector of coding are provided for a variable length decoder (VLD) 130.
At inverse quantizer 140, according to being transformed into one group of discrete cosine transform coefficient by the discrete cosine transform coefficient that the quantization step and the interframe/frame mode signal of line L10 and L12 coupling will be organized quantification respectively by demultplexer 120.This group discrete cosine transform coefficient is supplied to sef-adapting filter 150 by line L20.
According to the present invention, sef-adapting filter 150 receptions are coupled to its this group discrete cosine variable coefficient in proper order by line L20; Calculating is stored it by the standard deviation of the current frame data that line L14 is provided by frame memory 190 as previous standard deviation; According to the spatial character of calculating current frame data corresponding to a plurality of different standard deviation decoded before obtaining present frame; High frequency composition with should organize discrete cosine transform coefficient according to the spatial character filtering adaptively of present frame offers inverse discrete cosine transformer (IDCT) 160 with one group of discrete cosine transform coefficient through filtering by line L22 thus.The operation of sef-adapting filter 150 elaborates with reference to Fig. 2 and 3.
The more detailed block diagram of sef-adapting filter shown in Fig. 2 150 includes a standard deviation calculating section 152, a control signal generation part 154 and a filtering part 156.
The current frame data of presenting to sef-adapting filter 150 by line L14 is coupled to standard deviation calculating section 152.152 pairs of standard deviation computings in addition of being coupled to its frame data (for example current frame data) from frame memory 190 of standard deviation calculating section are with by utilizing its standard deviation to represent the statistical nature of frame data.
For example, frame data contain under the situation that resembles M * N pixel value (M and N are respectively positive integer), and its mean value and standard deviation are determined by following:
In the formula, MIp represents flat value; (x is y) for being positioned at coordinate (x, pixel value y) of a frame for Ip; And ACT shows standard deviation.
In the following formula, the relatively big value of the standard deviation that is calculated just means that the video image of corresponding frame data is very complicated.
Be provided for control signal generation part 154 and be stored in wherein the memory (not shown) by above-mentioned definite standard deviation as previous standard deviation.
Control signal generation part 154 is according to leaving the spatial character that a plurality of previous standard deviation in its memory produces this present frame in, and wherein these previous standard deviations are corresponding to each frame data that draws decoding before the current frame data.In detail point is said, the spatial character of current frame data is on average come to determine by the standard deviation to 30 previous frames handling in second for example.
Once the average deviation that calculates as the spatial character of present frame, control signal generation part 154 promptly provides a filtering control signal FC1 to filtering part 156, and wherein filtering control signal FC1 is definite by another predetermined threshold value of spatial character TH1 being compared come.
According to one embodiment of the present of invention, it is as follows that this control signal produces part 154 generation filtering control signal FC1:
If FC1=1 were MACT≤TH1+0.5 * Se
If 2 TH1+0.5 * Se＜MACT≤TH1+1 * Se
If 3 TH1+1 * Se＜MACT≤TH1+1.5 * Se
If 4 MACT＞TH1+1.5 * Se formula 3 wherein MACT is represented the spatial character of present frame; TH1 is a predetermined threshold value; Show the adaptive-filtering parameter with Se.
According to formula 3, filtering control signal FC1 is by considering spatial character, predetermined threshold TH1, and the correlation between the adaptive-filtering parameter S e is determined.Adaptive-filtering parameter S e is a test value, is given as the weight of the different value of determining the filtering control signal.The filtering control signal FC1 that is produced is added to filtering part 156.
According to filtering control signal FC1, filtering part 156 is selected to desire to give the zone of filtering and the discrete cosine transform coefficient in institute's favored area is shielded.
Referring to Fig. 3, it illustrates the filter field that is used for discrete cosine transform coefficient in the frequency domain, and wherein: (u v) is the discrete cosine transform coefficient in the frequency domain to Z, and u, V are 1 to K (for example 8); Z (0,0) expression DC composition; (u, frequency V) increases with the increase of u or V Z.If filtering control signal FC has numeral " 1 ", filtering part 156 is not promptly carried out filtering operation to this group discrete cosine transform coefficient; If it has numeral " 2 ", promptly be set to digital value " 0 " with the radio-frequency component in the lower area at dotted line B1; If it has numeral " 3 ", the following radio-frequency component of dotted line B2 is set to digital value " 0 "; And if it has a numeral " 4 ", the following radio-frequency component of dotted line B3 is set to digital value " 0 ".Be imported into inverse discrete cosine transformer 160 as above determined this group through the discrete cosine transform coefficient of filtering.
In said process, filter field and filtering control signal FC1 can be adjusted according to another embodiment of the present invention.
Again later referring to Fig. 1, inverse discrete cosine transformer 160 will be organized the discrete cosine transform coefficient through filtering of being fed by sef-adapting filter by line L22 and be transformed into one group of inverse discrete cosine transform data, then this group inverse discrete cosine transform coefficient be offered adder 180.
Meanwhile, motion compensator 170 extracts corresponding pixel data according to the motion vector that is transmitted by variable length decoder 130 by the frame data that leaves in the frame memory 190, and the pixel data that extracted is offered adder 180 as the data of motion compensation.
In adder 180, to be added to or not be added to from these group inverse discrete cosine transform data of inverse discrete cosine transformer 160 on the data from the motion compensation of motion compensator 170 according to the interframe on the circuit L12/frame mode signal, generate decoded image thus.As be inter-frame mode, this group inverse cosine transform data just is added on the data of motion compensation; And as being frame mode, just should organizing the inverse discrete cosine transform data and deliver to frame memory 190 and do not do any add operation by adder 180.
Decoded image is used as frame data and deposits into frame memory 190, and is sent to number-Mo (D/A) converter 200 as decoded vision signal.This decoded picture also is sent to sef-adapting filter 150 so that be used to produce its standard deviation as current frame data by circuit L14.
Digital-to-analog converter 200 becomes analog video signal with decoded video signal conversion, thus it is provided to a display unit (not shown) to show it.
According to the present invention, the complexity of current frame data is averaged to determine by the standard deviation to the pixel value of a plurality of different frames of decoding before obtaining current frame data.That is, determine that according to the average deviation current frame data is complicated and the radio-frequency component of the insensitive current frame data of human visual system is carried out filtering, reduces the reduction of the image quality that causes because of quantization error thus effectively.
Though the description of this invention only is at some preferred embodiment, also can make other modification and modification and do not deviate from spirit and the scope that in listed claim, proposes.
Claims (14)
1, be used for by the method that the decoding video signal that is encoded is produced decoded video signal, wherein this decoded video signal comprises a plurality of frames, and described method comprises step:
(a) adopt variable-length decoding to handle the vision signal that is encoded and obtain one group of discrete cosine transform coefficient that is quantized thus corresponding to current frame data;
(b) will organize the discrete cosine transform coefficient that quantizes and be transformed into one group of discrete cosine transform coefficient;
(c) basis decoded frame data before obtaining current frame data detects the spatial character of current frame data;
(d) according to the radio-frequency component of this group discrete cosine transform coefficient in spatial character filtering one presumptive area of this group discrete cosine transform coefficient and current frame data, produce one group of discrete cosine transform coefficient thus through filtering;
(e) discrete cosine transform coefficient that will organize through filtering is transformed into one group of inverse discrete cosine transform data;
(f) generate current frame data according to these group inverse discrete cosine transform data and frame data by using motion compensation; With
(g) current frame data is provided as decoded vision signal.
2. method described in the claim 1 is characterized in that step (c) includes step:
(c1) standard deviation of calculating frame data;
(c2) standard deviation corresponding to a plurality of previous frames processed before obtaining present frame is averaged; With
(c3) with the spatial character of average deviation as current frame data.
3. method described in the claim 2 is characterized in that step (d) comprises step:
(d1) spatial character and a predetermined threshold are made comparisons to produce the filtering control signal; With
(d2) for generating the filtered discrete cosine transform coefficient of this group, according to the radio-frequency component of this group discrete cosine transform coefficient in the filtering control signal filtering presumptive area.
4. method described in the claim 3 is characterized in that the radio-frequency component that is the discrete cosine transform coefficient in this presumptive area is set to digital value " 0 ".
5. method described in the claim 4 is characterized in that the radio-frequency component for this group discrete cosine transform coefficient of self adaptation filtering, and the filtering control signal has more than two logic levels.
6. method described in the claim 5 is characterized in that the filtering control signal is decided to be:
If FC1=1 were MACT≤TH1+0.5 * Se
If 2 TH1+0.5 * Se＜MACT≤TH1+1 * Se
If 3 TH1+1 * Se＜MACT≤TH1+1.5 * Se
If 4 MACT＞TH1+1.5 * Se wherein: FC1 is the filtering control signal; MACT represents the spatial character of current frame data; TH1 is a predetermined threshold value; And Se represents to be used as the adaptive-filtering parameter of the power of the different value of determining the filtering control signal.
7. method described in the claim 6 is characterized in that presumptive area changes according to the filtering control signal, and this presumptive area becomes to bigger when the value of filtering control signal increases.
8. the decoding video signal that is encoded is produced the equipment of decoded video signal, wherein decoded video signal comprises a plurality of frames, comprising:
Be used to be stored in the device that draws the frame data of decoding before the current frame data;
Utilize variable-length decoding to handle and be encoded video data to obtain the device of one group of discrete cosine transform remainder thus through quantizing;
Be used for to organize the device that the quantized-dct transformation of coefficient becomes one group of discrete cosine transform coefficient;
Radio-frequency component according to this group discrete cosine transform coefficient in this group discrete cosine transform coefficient and frame data filtering one presumptive area produces one group of device through the discrete cosine transform coefficient of filtering thus;
Be used for to organize the device that is transformed into one group of inverse discrete cosine transform data through the discrete cosine transform coefficient of filtering;
Utilize motion compensation to generate the device of current frame data according to these group inverse discrete cosine transform data and frame data; With
Be used for current frame data is delivered to storage device as new frame data and the device of this current frame data as decoded video signal is provided.
9. according to the equipment of claim 8, it is characterized in that filter comprises:
Detect the device of the spatial character of the complexity of representing current frame data according to frame data;
This spatial character and a predetermined threshold are made comparisons to produce the device of filtering control signal; With
For generating one group of discrete cosine transform coefficient, according to the device that should organize the radio-frequency component of discrete cosine transform coefficient in the filtering control signal filtering presumptive area through filtering.
10. according to the equipment of claim 9, it is characterized in that this checkout gear comprises:
Be used to calculate the device of the standard deviation of frame data;
The memory device of storage standards deviation;
To the device that the standard deviation that leaves in the storage arrangement averages, wherein, standard deviation is corresponding to a plurality of previous frames of handling before obtaining present frame; With
The device of average deviation as the spatial character of current frame data is provided.
11., it is characterized in that the radio-frequency component of this group discrete cosine transform coefficient in the presumptive area is set to a digital value " 0 " according to the equipment of claim 10.
12. according to the equipment of claim 11, it is characterized in that the high fdrequency component for this group discrete cosine transform coefficient of filtering adaptively, the filtering control signal has the logic level more than two.
13., it is characterized in that the filtering control signal is confirmed as according to the equipment of claim 12:
If FC1=1 were MACT≤TH1+0.5 * Se
If 2 TH1+0.5 * Se＜MACT≤TH1+1 * Se
If 3 TH1+1 * Se＜MACT≤TH1+1.5 * Se
If 4 MACT＞TH1+1.5 * Se wherein: FC1 is the filtering control signal; MACT represents the spatial character of current frame data; TH1 is a predetermined threshold value; And Se represents that one is used as the adaptive-filtering parameter of the power of the different value of determining the filtering control signal.
14. according to the equipment of claim 13, it is characterized in that presumptive area increases with the filtering control signal, the width of this presumptive area becomes big when the filtering control signal increases.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| KR1019960036970A KR100229533B1 (en) | 1996-08-30 | 1996-08-30 | Improved image decoding system |
| KR36970/96 | 1996-08-30 |
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| CN1175855A true CN1175855A (en) | 1998-03-11 |
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| CN97116864A Pending CN1175855A (en) | 1996-08-30 | 1997-09-01 | Method and apparatus for compensating quantization errors of decoded video signal by using adaptive filter |
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| KR (1) | KR100229533B1 (en) |
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|---|---|---|---|---|
| JP4885690B2 (en) | 2006-11-28 | 2012-02-29 | 株式会社エヌ・ティ・ティ・ドコモ | Image adjustment amount determination device, image adjustment amount determination method, image adjustment amount determination program, and image processing device |
| JP5087368B2 (en) * | 2007-10-30 | 2012-12-05 | 株式会社エヌ・ティ・ティ・ドコモ | Image processing apparatus, image processing method, and image processing program |
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| US5454051A (en) * | 1991-08-05 | 1995-09-26 | Eastman Kodak Company | Method of reducing block artifacts created by block transform compression algorithms |
| KR970009302B1 (en) * | 1993-08-17 | 1997-06-10 | Lg Electronics Inc | Block effect reducing apparatus for hdtv |
| JP2673778B2 (en) * | 1994-02-22 | 1997-11-05 | 国際電信電話株式会社 | Noise reduction device for video decoding |
| US5777679A (en) * | 1996-03-15 | 1998-07-07 | International Business Machines Corporation | Video decoder including polyphase fir horizontal filter |
| JP4170283B2 (en) * | 2004-11-01 | 2008-10-22 | 株式会社ソニー・コンピュータエンタテインメント | Drawing processing apparatus and drawing processing method |
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| JPH1098727A (en) | 1998-04-14 |
| KR100229533B1 (en) | 1999-11-15 |
| KR19980017211A (en) | 1998-06-05 |
| GB9718397D0 (en) | 1997-11-05 |
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