CN1322740C - Post-filter, post-filtering method and video signal decoder - Google Patents
Post-filter, post-filtering method and video signal decoder Download PDFInfo
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- CN1322740C CN1322740C CNB200410047671XA CN200410047671A CN1322740C CN 1322740 C CN1322740 C CN 1322740C CN B200410047671X A CNB200410047671X A CN B200410047671XA CN 200410047671 A CN200410047671 A CN 200410047671A CN 1322740 C CN1322740 C CN 1322740C
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Abstract
The present invention relates to a post-filter, post-filtering method and video signal decoder. A filter decision unit (111) makes a decision as to whether a block distortion is occurring at a block boundary or not using the amplitude value of at least one pixel in front and rear of the block boundary, respectively, and delivers a decision result to a filter (112). Upon receiving a decision result that a block distortion is occurring at the block boundary, the filter (112) performs filtering on a decoded video signal using the amplitude value of at least one pixel in front and rear of the block boundary, respectively, and delivers the filtering result as a display video signal. Since operational volume can be reduced, circuit scale and power consumption can be reduced.
Description
Technical field
The present invention relates to the postfilter that in the code translator that vision signal is deciphered, uses, such as, the piece distortion that will produce in the time of will encoding in the video display devices of the portable terminal of portable phone etc. and TV telephone system etc. reduces and even its elimination is made the technology of its performance true value.
Background technology
At the various video compression standard, such as, ITU-T, H.263, among the MPEG (Motion Picture Experts Group) 1, MPEG2, MPEG4 etc., in order to be that several fritters compress with image segmentation, along with the increase of compression ratio, tangible piece distortion can take place in the border of piece.For solving this distortion, several solutions have been proposed.
Such as, the technology of filtering is carried out in the piece distortion that takes place according to the information of motion compensation on block boundary has been proposed in following patent documentation.
In addition, also in following non-patent literature, proposed when filtering is judged, used block boundary to carry out the technology of determination processing in abutting connection with 8 pixels.
TOHKEMY 2002-330436 communique (the 1-24 page or leaf, Fig. 1)
ITU-T, " ISO/IEC14496-2:2001 ", in July, 2002, p.449-451
Summary of the invention
But, in existing technology, utilize motion vector to carry out the flow process of multistage decision, have the big problem of operand owing to adopt.So because operand is big, if consider to utilize electronic circuit to realize this calculation process, certainly will produce circuit scale must very big problem.This point is particularly very remarkable in the technology of above-mentioned patent documentation 1.
In addition, in the motion of above-mentioned non-patent literature 1,, as judging key element, there is this very big problem of operand that is used for determination processing and Filtering Processing in a lot of adjacent pixels because when filtering is judged.In addition, if operand is big, power consumption must increase.Power consumption increases, and particularly in the little machine of battery capacities such as portable terminal, becomes very big problem.
The present invention finishes in order to solve above-mentioned such problem, and its purpose is that reducing circuit scale by the minimizing operand reduces power consumption.
Technical scheme of the present invention provides a kind of postfilter and postfilter processing method, wherein, this postfilter is to be disposed to be decoding video signal after unit carries out encoding process with the piece, and the postfilter of the back level of the decoding circuit exported as decoded video signal of the signal that will decode, it is characterized in that: have judgement produces the piece distortion in block boundary determinant, to clip block boundary adjacent when being contained in a mat woven of fine bamboo strips N-1 piece in the above-mentioned decoded video signal and N piece, be positioned at this N-1 piece, the pixel amplitude of the pixel c of close this block boundary is C, be positioned at N piece of this mat woven of fine bamboo strips, the pixel amplitude that clips the adjacent pixel d of above-mentioned block boundary and above-mentioned pixel c is D, on the extended line that connects above-mentioned pixel c and above-mentioned pixel d, adjacent with above-mentioned pixel c, the pixel amplitude of pixel b that is positioned at the piece of above-mentioned N-1 is B, adjacent with above-mentioned pixel d, when the pixel amplitude that is positioned at the pixel e of above-mentioned N piece is E, the position of the above-mentioned block boundary on above-mentioned extended line makes x=0, make x＞0 in above-mentioned N the piece, make x＜0 in above-mentioned N-1 the piece, and working as with the pixel is under the situation of unit, the position of pixel b is x=-1.5, the position of pixel c is x=-0.5, the position of pixel d is x=0.5, when the position of pixel e is x=1.5, producing on the above-mentioned block boundary under the situation of piece distortion when being judged as, according to following formula with above-mentioned pixel b, c, d, the pixel amplitude of e is modified to Y
Y＝α1-β·γ
λx (x＞0)·····(1)
Y＝α2+β·γ
λx (x＜0)·····(2)
Wherein, α 1, α 2, β are the real numbers that satisfies α 1-α 2=2 β, and γ, λ are the constants of being scheduled to.
In addition, the present invention also provides a kind of video signal decoding apparatus, it is characterized in that: have the postfilter described in the technique scheme, and decoding circuit.
Description of drawings
Fig. 1 is the block diagram of formation that the vision signal code translator of example 1 of the present invention is shown.
Fig. 2 is the diagrammatic sketch of input signal that the coded system of example 1 of the present invention is shown.
Fig. 3 is the diagrammatic sketch that the definition block border pixel value on every side of example 1 of the present invention is shown.
Fig. 4 is the flow chart that the filtering determination step of example 1 of the present invention is shown.
Fig. 5 is the flow chart that another filtering determination step of example 1 of the present invention is shown.
Fig. 6 is the processing diagrammatic sketch that the filter A of example 1 of the present invention is shown.
Fig. 7 is the diagrammatic sketch that another postfilter formation of example 1 of the present invention is shown.
Fig. 8 is the processing diagrammatic sketch that the filter A of example 2 of the present invention is shown.
Fig. 9 is the diagrammatic sketch of formation that the postfilter of example 3 of the present invention is shown.
Figure 10 is the flow chart that the filtering determination step of example 3 of the present invention is shown.
Figure 11 is the processing diagrammatic sketch that the filter B of example 3 of the present invention is shown.
Figure 12 is the diagrammatic sketch that the tables of data of example 5 of the present invention is shown.
Figure 13 is the block diagram of formation that the vision signal code translator of example 6 of the present invention is shown.
Figure 14 is the diagrammatic sketch that the postfilter formation of example 6 of the present invention is shown.
Figure 15 is the diagrammatic sketch that another postfilter formation of example 6 of the present invention is shown.
Figure 16 is the flow chart that the filtering determination step of example 6 of the present invention is shown.
Figure 17 is the flow chart that another filtering determination step of example 6 of the present invention is shown.
Figure 18 is the block diagram of formation that the vision signal code translator of example 7 of the present invention is shown.
Figure 19 is the diagrammatic sketch of formation that the postfilter of example 7 of the present invention is shown.
Figure 20 is the diagrammatic sketch that another postfilter formation of example 7 of the present invention is shown.
Figure 21 is the flow chart that the filtering determination step of example 7 of the present invention is shown.
Figure 22 is the flow chart that another filtering determination step of example 7 of the present invention is shown.
Figure 23 is the block diagram of formation that the vision signal code translator of example 8 of the present invention is shown.
Figure 24 is the diagrammatic sketch of formation that the postfilter of example 8 of the present invention is shown.
Figure 25 is the diagrammatic sketch that another postfilter formation of example 8 of the present invention is shown.
Figure 26 is the flow chart that the filtering determination step of example 8 of the present invention is shown.
Figure 27 is the flow chart that another filtering determination step of example 8 of the present invention is shown.
Figure 28 is the diagrammatic sketch of formation that the postfilter of example 9 of the present invention is shown.
Figure 29 is the flow chart that the filtering determination step of example 9 of the present invention is shown.
Figure 30 is the diagrammatic sketch of processing that the filter A of example 9 of the present invention is shown.
Figure 31 is the diagrammatic sketch that the definition block border pixel value on every side of example 10 of the present invention is shown.
Figure 32 is the diagrammatic sketch of formation that the postfilter of example 10 of the present invention is shown.
Figure 33 is the flow chart that the filtering determination step of example 10 of the present invention is shown.
Figure 34 is the diagrammatic sketch of processing that the filter C of example 10 of the present invention is shown.
Embodiment
According to illustrated example the present invention is illustrated below.
Example 1
Fig. 1 is the schematic block diagram of formation that the vision signal code translator of example 1 of the present invention is shown.In addition, in each example 1～10 of the present invention, for simplicity, the example of description is to use the video compression standard of mpeg 4 standard as the vision signal code translator.But theme of the present invention is if to the vision signal code translator of the decoding coded video signals that to be unit with the piece obtain encoding video signal, just can be applied to all this kind devices.As this kind device, the vision signal code translator of the video compression standard that uses MPEG1, MPEG2, H.263 waits is arranged.
As shown in Figure 1, the major part of vision signal code translator is roughly by decoding circuit 100 be disposed at level thereafter or the postfilter 109 of outlet side constitutes.Particularly, become the postfilter 109 of the core of this example, except also this input decoding video signals being carried out the Filtering Processing (interpolation processing) that reduces or eliminate the piece distortion the specific filtering judgement to implementing from the decoding video signals of decoding circuit 100 outputs.The function of this postfilter 109 is narrated below.
At first, the formation and the action of decoding circuit 100 are described.Input-buffer 101 receives the also basic stream of store M PEG4.In addition, be sent to variable length decoder 102 at the basic stream of input-buffer 101 stored and carry out variable length decoding, its result, data such as variable length decoder 102 output factor data, motion vector data.Among the output of variable length decoder 102, coefficient data is delivered to inverse quantizer 103 and is carried out re-quantization.So inverse quantizer 103 sends to inverse DCT device 104 as input with this output.In addition, inverse DCT device 104 carries out inverse dct transform, generates and output frame image (in-frame encoding picture, inter prediction encoding image, bidirectionally predictive coded picture).Its result, this two field picture is supplied with and is carried out the synthetic adder 105 of image.On the other hand, motion vector data is supplied with motion compensator 108.
When above-mentioned two field picture was in-frame encoding picture, adder 105 outputed to postfilter 109 as decoding video signals with this two field picture former state is constant.On the other hand, when above-mentioned two field picture is inter prediction encoding image or bidirectionally predictive coded picture, the output of the output of motion compensator 108 and inverse DCT device 104 is in adder 105 additions, and adder 105 outputs to postfilter 109 with this addition result as decoding video signals.In addition, decoding video signals also is input to the preceding frame memory 106 of decoding circuit 100 inside and shows frame memory 107.
Preceding frame memory 106 is preserved the image of the former frame of the image of now deciphering, and existing frame memory 107 is preserved the present image of deciphering.So, the input of motion compensator 108 is supplied with in the output of the output of preceding frame memory 106 and existing frame memory 107 together, when the output of inverse DCT device 104 is inter prediction encoding image or bidirectionally predictive coded picture, in motion compensator 108, before using the output of frame memory 106 and from the backward-predicted of the motion vector of forward prediction, the output of using existing frame memory 107 and the variable length decoder 102 of the motion vector of variable length decoder 102, also have the motion compensation two field picture of bi-directional predicted formation, be input to adder 105.
In mpeg 4 standard, as shown in Figure 2, vision signal is divided into macro block, carry out data compression with the block unit of further sectionalization.Therefore, to carrying out data compression according to mpeg 4 standard coded data implement in the decoding video signals that decoding obtains, the situation of the tangible piece distortion in border that is created in the vision signal before the coding non-existent is a lot.Therefore, decoding video signals, be transformed to the display video signal that makes the piece distortion reduce or eliminate by back grade the postfilter 109 that is disposed at decoding circuit 100, and, utilize display buffer 110, after the vision signal of the standard of being transformed to, send to display unit (not shown) etc. mostly.
Below, the formation and the action of the postfilter 109 that constitutes the core are described.Postfilter 109, such as, pixel value B, C, D, the E before and after the block boundary carries out the piece distortion in the block boundary as shown in Figure 3 judgement and Filtering Processing utilized.Postfilter 109, its formation comprises (i) pixel value (B of Fig. 3, C, D, E count 4 pixel values) according to each 2 pixel of the front and back that are included in the block boundary in the decoding video signals, judges the filtering determinant 111 that whether the piece distortion takes place in block boundary and this result of determination is exported; And (ii) when the result of determination that receives from the distortion of the generation piece of filtering determinant 111, according to each 2 pixel value (B of Fig. 3, C, D, E counts 4 pixel values) of the front and back of block boundary, carry out the Filtering Processing of decoding video signals and (mat woven of fine bamboo strips 1) filter that the vision signal after the Filtering Processing is exported as display video signal (below be called filter A) 112.
In other words, the decoding video signals of the output of adder 105 as filtering determinant 111 and the input of filter A112 two-way, is supplied with postfilter 109.In addition, will narrate below about the decision method or the determination processing action of filtering determinant 111.When filtering determinant 111 utilized decision method described later to be judged to be the distortion of generation piece, filtering determinant 111 to filter A112, sent the control signal as the ON signal of command execution Filtering Processing.Relative therewith, be judged to be when taking place certainly not distort, filtering determinant 111 to filter A112, sends the control signal of not carrying out the OFF signal of Filtering Processing as order.Filter A112, the order of corresponding this ON signal is carried out and is reduced or eliminates (the 1st) Filtering Processing (its details aftermentioned) of piece distortion and will reduce or eliminate the display video signal that piece distorts to output to display buffer 110 from decoding video signals.On the other hand, when control signal was OFF, filter A112 did not reduce or eliminates the Filtering Processing of piece distortion, outputed to display buffer 110 as decoding video signals with the decoding video signals former state of input is constant.
The effect of postfilter 109 is to reduce or eliminate the piece distortion that takes place at the block boundary place.Herein, so-called " piece distortion " refers to the state of the stair-stepping difference that produces between the amplitude (following amplitude with 1 pixel is called " pixel value ") of the pixel before and after the block boundary.
At first, pixel value around the block boundary, it is each in the pixel value (counting 4 pixel values) of each 2 pixel of front and back of block boundary, as shown in Figure 3, respectively by the pixel value C of the pixel c in certain tight the place ahead of block boundary, in pixel c front one pixel b pixel value B, in the pixel value D of the pixel d at this tight rear of block boundary, one the pixel value E definition of pixel e in pixel d back.Herein, so-called " pixel value " is brightness, color difference signal or rgb value etc.
In this example, in order to distinguish occasion and the original border of image that the piece distortion takes place in block boundary, not to carry out Filtering Processing forever, but whether the judgement of piece distortion takes place in filtering determinant 111 shown in Figure 1.So filtering determinant 111 utilizes the pixel value B～E of the pixel around the block boundary, the two pixel value B and the difference between the C of carrying out before and after the border are the piece distortion, perhaps are not the judgements of piece distortion.In the occasion that original vision signal is divided into block unit, accidental, also can produce the occasion on the value border of pixel at block boundary.At this moment, general, if when the difference of two pixel values before and after the border is relatively very big, great changes have taken place just can to think color.But, the piece distortion that takes place owing to amount of information is not enough, can produce the edge in simulation ground because continually varying is local on pixel value originally, can think the absolute value of two margin of image element before and after the block boundary of the occasion that becomes piece distortion, the absolute value of the difference of the border pixel values that has than original image is little.So, be conceived to this point, filtering determinant 111, the absolute value of two margin of image element before and after the block boundary is less than the occasion of setting (below be called " the 1st threshold value "), and decidable distorts for there being piece.
An example in the filtering determination processing of filtering determinant 111 shown in the flow chart of Fig. 4.Wherein, supposing to be used for the above-mentioned mat woven of fine bamboo strips 1 threshold value that Filtering Processing judges represents with K.At this moment, filtering determinant 111, in the step 201 of Fig. 4,
0＜|C-D|＜K......(1)
According to the mat woven of fine bamboo strips 1 arithmetic expression that formula (1) provides, carry out on this block boundary, having or not the judgement of margin of image element.
Filtering determinant 111 is judged the occasion that has margin of image element when confirm the establishment of the 1st arithmetic expression in this step 201, and filtering determinant 111 is also in step 202a
B=C and D=E...... (2)
Whether whether the 2nd arithmetic expression that evaluation is provided by formula (2) sets up decidable is the piece distortion.So, set up if confirm the 2nd arithmetic expression, then there is the piece distortion in filtering determinant 111 with regard to judging, filter A112 is sent the ON signal.
Wherein, narration is the 1st threshold k.When if the border of pixel value overlaps on block boundary accidentally, when the value of the 1st threshold k was very big, the distortion of decidable piece reached the border of this pixel that should have always.According to inventor's experiment, with 8bit (256 grade) when providing, the value in the scope of setting about K=10 to K=40 is the occasion of threshold k at pixel value, can obtain the effect that the piece distortion reduces, and the destruction of profile portion is few, can obtain good result.
Filtering determinant 111, as shown in Figure 4, with formula (2) (the 2nd arithmetic expression) as decision condition.This is the few occasion of amount of information of distributing because of when encoding, the piece of process decoding, and the possibility height that block boundary information on every side is short of is roughly the event of the occasion that satisfies formula (2) in the occasion that becomes the piece distortion.On the other hand, do not satisfy the occasion of formula (2) satisfying formula (1), this roughly is included in the occasion of the pixel boundary in the original vision signal.Such as, the occasion of striped apperance.Because this effect can improve the precision that the piece distortion is judged.In addition, the judgement of formula (1) shown in Figure 4 and formula (2) order or step 201,202a also can change.
Like this, judging according to the establishment of formula (2) to have the piece distortion, promptly detect stair-stepping variation, is very effective.
In above-mentioned description, be used to detect the judgement of stair-stepping variation, undertaken by formula (2), since but pixel value is a digital value, judge the problem that on pixel value, has difference with regard to existing with the difference of 1 grade.So the form that formula (2) is replaced into formula (3) also is possible.In this occasion, formula (3) is defined as the 2nd arithmetic expression.
| B-C|＜L and | D-E|＜L...... (3)
But the 2nd threshold value L in the formula (3) compares with the 1st threshold k, is very little value, such as, make L=2.Inventor's experiment shows that to formula (2) displacement like this, the effect of invention is also constant.Flow chart when use formula (1) and formula (3) is shown in Fig. 5.Fig. 5 is that step 202a that the flow chart of Fig. 4 is shown becomes the difference for step 202 this point.
Concrete example to the Filtering Processing of filter A112 is illustrated below.Wherein, the Filtering Processing that filter A112 has, determined as Fig. 6.Being Filtering Processing shown in Figure 6, is the linear interpolation that utilizes formula (4).
Y＝|B-E|/3×x+(C+D)/2......(4)
As shown in Figure 6, filter A112 is the filter that pixel value B, C, D, E is carried out linear interpolation.Wherein, Y is corresponding to new pixel value.Promptly corresponding to C1, the D1 of Fig. 6, when x=-0.5, Y=C1, and when x=0.5, Y=D1.
As above, in this example, utilize the pixel value of each 2 pixel (amounts of 4 pixels of meter) of the front and back of block boundary, by (I) from whether being stepped and the extent of pixel value is judged and had or not the piece distortion and (II) again pixel value C, the D linear interpolation of each 1 pixel of boundary portion are carried out to proofread and correct and carry out Filtering Processing.Owing to be such formation,, can obtain few and the postfilter that image deterioration is little of operand according to this example.
Utilize the measured value of table 1 and the table 2 pair filter that in this example, illustrates to be illustrated below.Shown in the table 1 is the environment that carries out the instrumentation of Filtering Processing time, and that use is MPEG4 and picture dimension QVGA (320 pixels * 240 row).Shown in the table 2 is the instrumentation time.In addition, comprise in the time at the instrumentation of table 2 and utilize bit rate to be the decoding time of 384kbps frame rate for 15fps.
As shown in Table 2,2 pixels are judged 2 pixel filters, compare just enough for few time far away with conventional example.In addition, compare, can see that image quality improving has very big effect with the occasion that does not have filter.
[table 1]
The instrumentation environment
| OS | Windows (registered trade mark) |
| CPU | Pentium3 (registered trade mark) 800MHz |
[table 2]
The instrumentation time
| The filter title | Do not have | Conventional example | 2 pixels are judged 2 pixel filters |
| Maximum time | 25 | 61 | 27 |
| Average time | 20 | 54 | 22 |
Unit: ms
In addition, in this example, the ON/OFF signal that filtering determinant 111 sends is exported filter A112, according to having or not of the Filtering Processing of the signal determining that receives in filter A112, but formation that also can be is as shown in Figure 7 carried out Filtering Processing in filter A112, and the switching signal of sending according to filtering determinant 111, or the output of selective filter A112, or select decoding video signals 115 both one of.In following example, also can adopt the formation of postfilter 109 as shown in Figure 7.
Example 2
This example 2 is results that the bearing calibration to the filter A112 of example 1 improves, and does not have difference in other respects.So, in this example, also quote Fig. 1 to Fig. 5.In other words, this example is characterised in that, as shown in Figure 8, be the level and smooth interpolation processing of the function by utilizing regulation and each 2 pixel value of front and back of block boundary are carried out level and smooth interpolation this point change for the pixel value of each 2 pixels (count 4 pixel values) of the front and back of block boundary.
In Fig. 8, utilize formula (5) and formula (6) to carry out interpolation herein.
Y＝(C+D)/2+((B-E)×(1-2^(λx)) (x＞0)......(5)
Y＝(C+D)/2-((B-E)×(1-2^(λx)) (x＜0)......(6)
Wherein, in formula (5) and formula (6), be to utilize 2 power, no matter be natural number, or rational, surd power can.But, must be number greater than 0.
f(x)＝(1-2^(λx))......(7)
m(x)＝K/3x......(8)
|m(x)-f(x)|＞0(x≤|1.5|)......(9)
The part of formula (5) and formula (6) defines like that suc as formula (7).In addition, the greatest gradient of the interpolation straight line when carrying out linear interpolation as implementing form 1 is filtering decision content K/3, definition (8).At this moment, formula (7) is the function of the monotone increasing by initial point and formula (9) preferably.If these conditions are satisfied in design, just can set the interpolation formula of the filter A112 of example 2.In other words, the interpolation formula of the filter A112 of example 2 also can be provided by following formula (10) and formula (11).
Y＝(C+D)/2+((B-E)×(1-exp(λx)) (x＞0)......(10)
Y＝(C+D)/2-((B-E)×(1-exp(λx)) (x＞0)......(11)
λ in formula (5), formula (6), formula (7), formula (10) and the formula (11) must satisfy formula (9), according to inventor's experiment, recognizes and sets the λ value in the scope that is preferably in about λ=0.1 to 0.01.
Adopt this formation, just can carry out level and smooth block boundary interpolation processing (level and smooth interpolation processing) (with reference to after 4 corrections shown in Figure 8 pixel value B1～E1), image quality can improve.And the determination flow that need not to change postfilter shown in Figure 5 109 just can be carried out the image quality adjustment of filter simplely.
Example 3
Example 3 is characterised in that, the flow process (with reference to Fig. 5) of whether judgements in the postfilter 109 of the vision signal code translator of example 1 or 2 being carried out Filtering Processing changes this point.So, in this example, also quote two circuit 100 of Fig. 1 and 110 formation and action.
Herein, the formation of postfilter 109, replacing Fig. 1's is as shown in Figure 9.In other words, in Fig. 9, postfilter 109, its formation comprises the ON signal of the filtering determinant 111a output that (i) correspondence receives, each 2 pixel value according to the front and back of block boundary carry out the filter A112 for the 1st Filtering Processing of decoding video signals; And the ON signal of the (ii) corresponding filtering determinant 111a output that receives, each 2 pixel value according to the front and back of block boundary carry out the filter B113 for the 2nd Filtering Processing of decoding video signals.In these filters, the filter A (Fig. 1) of filter A112 and example 1 is suitable.So, we can say that increasing filter B113 is the feature of this example.Therefore, postfilter 109, the switching signal that also comprises corresponding filtering determinant 111a output is to the 1st and the switch 114 that switches of the output of the mat woven of fine bamboo strips 2 filters 112,113.Details is as follows.
At first, the decoding video signals from adder 105 outputs is input to filtering determinant 111a, filter A112 and filter B113.In addition, narrate below about the decision method of filtering determinant 111a.
(I) at filtering determinant 111a, according to the input decoding video signals, judge the occasion that the piece distortion takes place, filtering determinant 111a, on the one hand, to filter A112, the ON signal (control signal) of the filtering action of this Filtering Processing is carried out in the output indication, on the other hand, send the filtering OFF signal (control signal) that does not carry out this Filtering Processing to filter B113.Meanwhile, filtering determinant 111a, indication is exported the output of filter A112 as the demonstration decoding video signals switching signal sends to switch 114.Its result, switch 114 switches to the outlet side of filter A112.Like this, through reducing or eliminate the demonstration decoding video signals of piece distortion, output and the switch 114 of process filter A112 output to display buffer 110.
(II) on the other hand, judge the occasion that the piece distortion takes place at filtering determinant 111a according to the input decoding video signals, filtering determinant 111a, send the OFF signal that this Filtering Processing is not carried out in indication to filter A112, otherwise, when the ON signal of this Filtering Processing is carried out in filter B113 transmission indication, will indicate the switching signal that the output of filter B113 is exported as final decoding video signals to send to switch 114.Its result, switch 114 switches to this switched terminal output one side of filter B113.So decoding video signals utilizing after filter B113 implements the 2nd Filtering Processing, as display video signal, sends to display buffer 110.
(III) relative therewith, judge the occasion that the piece distortion does not take place at filtering determinant 111a, filtering determinant 111a sends filtering OFF signal to filter A112 and filter B113 respectively, and switch 114 is switched to filter A side.In this occasion, switch 114, even filter A112 and any one output of filter B113 are connected with its output, because any side of filter A112 and filter B113 is not carried out Filtering Processing, the decoding video signals of the same content when having with input postfilter 109, the constant input as switch 114 of former state provides.So when not carrying out Filtering Processing, the decoding video signals former state is constant as showing that decoding video signals sends to display buffer 110.In addition, postfilter shown in Figure 9, also can, as shown in Figure 7, or the output of selective filter A112, or the output of selective filter B113, can be some formations of selecting decoding video signals 115.
Figure 10 is the flow chart that the filtering acts of determination of filtering determinant 111a is shown.At first, as filtering determinant 111a, in step 201, when decision block boundary pixel C, D do not satisfy formula (1), the difference between this block boundary pixel C, the D is not regarded as piece distortion, its result, judge and do not carry out Filtering Processing, send the OFF signal to two filters 112,113.In this occasion, as mentioned above, no matter the switching signal of filtering determinant 111a output is which of output of two filters 112,113 of indication, and the result is the same.
Secondly, as filtering determinant 111a, in step 202, judge that this block boundary is as 4 plain value B, C, D, when E satisfies formula (1) and do not satisfy formula (3), again determine in filter B113, to carry out the 2nd Filtering Processing, when a filter B113 to a side sent filtering ON signal, also the output indication switched to the switching signal to filter B113 output.In addition, about the Filtering Processing of filter B113, narration below.Relative therewith, as this block boundary 4 pixel value B, C, D, when E satisfies formula (1) and formula (3) simultaneously, filtering determinant 111a, judge and determine in filter A112, to carry out the intention of the 1st same Filtering Processing, filtering ON signal, filtering OFF signal, the switching signal of for this reason having described sent to filter A112, filter B113 and switch 114 respectively.
In the step 205 of Figure 10, filter B113 carries out such Filtering Processing that Figure 11 illustrates for example.This Filtering Processing is the interpolation processing that is provided by formula (5) and formula (6) or formula (10) and formula (11).Wherein, these functions preferably satisfy the function in the condition described in the example 2.But in example 3, filter A112 and filter B113 utilize same function to carry out interpolation processing together.In other words, when in filter A112, utilizing formula (5) and formula (6) to carry out the occasion of the 1st Filtering Processing, in filter B113, also carry out the 2nd Filtering Processing by formula (5) and formula (6) regulation.
Utilize such formation, the processing on block boundary is carried out more smoothly, can further improve image quality.And, because in the determination flow of postfilter 109, do not roll up operand (with reference to Figure 10), so can obtain only just can realize the advantage that further improves of performance of filter by a small amount of increase operand.
Example 4
Example 4 is characterised in that, as the filter A112 of example 3, the function of filter B113, uses other function this point mutually.
Such as, use formula (5) and formula (6) in filter A112, and in filter B113 use formula (10) and formula (11).Perhaps, it uses relation also can on the contrary.
By such formation, just can design flexibly filter.In other words, the processing that processing that filter 112 carries out and filter 113 carry out, identical, different, mutual contents processing is independently to concern.
Example 5
Example 5 is characterised in that, filter in the postfilter 109, have " in the arithmetic expression of in Filtering Processing, using; at each the position data of each 2 pixel values of the front and back of block boundary as the functional expression of variable; by the tables of data that each precalculated 4 value of each position data are constituted ", by this tables of data and each position data are carried out reference, carry out this Filtering Processing this point.In other words, the feature of example 5 be with the computing of any one Filtering Processing of example 1 to 4 all reference table simplify this point.
x＝“{-1.5、-0.5、0.5、1.5}......(12)
At example 1 to 4 among each, because from block boundary count apart from x, fixing like that suc as formula (12), can calculate the item (f (x)) about counting in the relevant arithmetic expression of in Filtering Processing, using in advance, this is constituted as the table data apart from each the value of calculating of x apart from x from block boundary.If such table data in advance is stored in filter A112, the filter B113, this filter, when carrying out this Filtering Processing, by the data in the above-mentioned table of reference, can carry out separately at this computing apart from the item f (x) of x, only by with the arithmetic section of irrelevant other of distance x, i.e. the computing with difference-product of the difference of pixel value etc. just can be carried out Filtering Processing.Such as, in the occasion of utilizing formula (5) and formula (6), the part of formula (7) is arranged in table (tableization), and the formation of this table is as shown in figure 12.In addition, in Figure 12, be the table data that the operation result with λ=0.1 in the formula of establishing (7) and formula (7) makes in the 3rd value that rounds up and obtain of decimal point.In addition,, in the table of Figure 12, used decimal, but because the arithmetic unit that generally carries out Filtering Processing has the bit shift function because pixel value is a positive number, also can be with the table of Figure 12 on duty with 2 power, obtain by final operation result is carried out bit shift.In addition, this example is being applied in the example 1, each of function part f (the x)=x/3 of formula (4) apart from each data all by tableization.
Because utilize the formation of this reference table, the operand in the time of can reducing the Filtering Processing in the filter, because the burden of the operational part in the filter that is made of CPU etc. alleviates, power consumption can reduce.And the advantage that operand reduces is also changed on a small scale to circuit contribution.
Example 6
Example 6 is characterised in that, the filtering determinant is the coding parameter setting threshold this point according to decoding circuit output.
In other words, among each form of example 1 to 5, the threshold k that is used for the Filtering Processing judgement is the fixed value of decision before decoding.Relative therewith, in example 6, utilize the formation shown in the block diagram of Figure 13, expand to the mode that postfilter 109a supplies with as input with coding parameter from variable length decoder 102a.Wherein, so-called coding parameter is with vision signal, such as, with the occasion that the mode of MPEG4 is encoded, the amount of feature being given this coding step.In coding parameter, quantization parameter Qp, an interior piece/piece ratio etc. are arranged.Wherein, so-called in a piece/piece ratio, be the ratio of the number that macro block is encoded as interior macro block and the number of encoding with a macro block, piece in saying/when a piece ratio is big, be that interior piece is many, encoding amount is many at this moment.In other words, an interior piece/piece ratio also can be used as the amount processing of coding being given feature.Below, for sake of convenience, use the example of quantization parameter Qp (below be called Qp) as coding parameter.In addition, in MPEG4, Qp can the scope between 1～31 in value.
When Qp was big, in the occasion of utilizing encoder to quantize, this encoding amount was little.In the little occasion of encoding amount of distributing, as decipher, the possibility that the piece distortion takes place is very big.On the other hand, at Qp hour, when utilizing encoder to quantize, its coding quantitative change was big, is difficult to take place the piece distortion.
In other words, by the filtering decision threshold being controlled, can use postfilter adaptively corresponding to Qp.Figure 14 and Figure 15 illustrate the formation of postfilter 109a.These configuration examples are respectively filtering determinant 111 or the filtering determinant 111a to Fig. 1 to Fig. 9, and coding parameter is supplied with as new input.The filtering decision flowchart of filtering determinant 111b or 111c is shown in Figure 16 and Figure 17 respectively.
In the example of Figure 16 or Figure 17, example 1 is replaced by formula (13) to example 5 each formulas (1).
0＜|C-D|＜Qp......(13)
By such change, can realize the Filtering Processing of the adaptivity that meets with encoding amount.
In addition, postfilter shown in Figure 14, as shown in Figure 7, it constitutes also can select some from the output of filter A112 or decoding video signals 115, and, postfilter shown in Figure 15, it constitutes the some of the output of the output that also can select from filter A112, filter B113 or decoding video signals 115.
Example 7
Example 7 is characterised in that, the filtering determinant is according to the controlling value from the outside input, sets the threshold value this point of both having stated.So-calledly be input to controlling value from the outside, such as, be value that is set by the user or the like.
In other words, among each form of example 1 to 5, the threshold k that is used for the Filtering Processing judgement is the fixed value of decision before decoding.Relative therewith, in example 7, this 1st threshold k can change according to the controlling value from the outside input.
The integral body of example 7 shown in Figure 18 constitutes.Postfilter 109b wherein accepts to newly arrive since the control of outside.Postfilter 109b is formed in shown in Figure 19 or Figure 20 in detail.These configuration examples are respectively filtering determinant 111 or the filtering determinant 111a to Fig. 1 or Fig. 9, will supply with as new input from the control of outside.
This controlled quentity controlled variable from the outside is defined as external control value α.In addition, new filtering threshold is defined as threshold value Th-i.
Th_i＝K+α......(14)
Th_i＝α......(15)
As update method based on the filtering threshold of external control value α, such as, formula (14) or formula (15) can be used.Wherein, in formula (14), the effect of external control value α is that the threshold k of determining as fixed value is originally adjusted.On the other hand, in formula (15), the effect of external control value α is that fixed value K is originally replaced.In addition, the filtering determinant also can use these formulas (14) and formula (15) in addition, or two formulas (14) and formula (15) is used in combination also can be at it different the time.
About new filtering threshold Th_i, each filtering determination flow of filtering determinant 111d or filtering determinant 111e is illustrated in Figure 21 or Figure 22.Among each of Figure 21 or Figure 22, step 201b arithmetic expression is to replace example 1 each formula (1) to example 5 with formula (16).
0＜|C-D|＜Th_i......(16)
By such formation,, can in the change threshold value, carry out filtering control according to controlling value from the outside input.And,, also can carry out Filtering Processing according to user's hobby because can be set by the user the external control value.
In addition, postfilter shown in Figure 19, as shown in Figure 7, it constitutes also can select some from the output of filter A112 or decoding video signals 115, and, postfilter shown in Figure 20, it constitutes the some of the output of the output that also can select from filter A112, filter B113 or decoding video signals 115.
Example 8
Example 8 is characterised in that, the filtering determinant is according to as the coding parameter of the output of decoding circuit and from the controlling value of outside input, setting threshold this point.
In other words, as previously mentioned, in example 6, be to use coding parameter as threshold value.This example can be accepted the control from the outside according to this coding parameter, changes threshold value.
The integral body of example 8 shown in Figure 23 constitutes.Postfilter 109c wherein for filtering threshold control, accepts coding parameter from variable length decoder 102a as input.Postfilter 109c is formed in shown in Figure 24 or Figure 25.These configuration examples are respectively filtering determinant 111 or the filtering determinant 111a to Fig. 1 or Fig. 9, supply with as the new input that is used for decision threshold with coding parameter with from the controlling value of outside.
So, when above-mentioned control signal from the outside is defined as external control value β, new filtering threshold is defined as threshold value Th_k.For simplicity, in the following description, adopt Qp as coding parameter.
Th_k＝Qp+β......(17)
Filtering threshold Th_k defines according to formula (17).According to the threshold setting of this formula (17), mean for being that the adaptivity Filtering Processing is carried out on the basis with the Qp value, can control the β value and carry out filtering control as biasing.
About new filtering threshold Th_k, the filtering determination processing flow chart that carries out of filtering determinant 111f or filtering determinant 111g is shown in Figure 26 or Figure 27 respectively.At each step 201c of Figure 26 or Figure 27, each formula (1) that is equivalent to example 1 to 5 is replaced the result who forms by formula (18).
0＜|C-D|＜Th_k......(18)
By such formation, can when not damaging adaptivity and carrying out filtering control, also can carry out Filtering Processing according to user's hobby.
In addition, postfilter shown in Figure 24, as shown in Figure 7, it constitutes also can select some from the output of filter A112 or decoding video signals 115, and, postfilter shown in Figure 25, it constitutes the some of the output of the output that also can select from filter A112, filter B113 or decoding video signals 115.
Example 9
In example 1 to 8, what illustrate is in the filtering determinant, use each 2 pixel of front and back of block boundary to implement the example of the judgement of pieces distortion, in this example, the occasion of each 1 pixel of the front and back of using block boundary being implemented the judgement of piece distortion is illustrated.
Consider each 1 pixel value C, D that pixel is Fig. 3 of block boundary.And the configuration example of postfilter 109 is shown in Figure 28.Postfilter shown in Figure 28 is in the filtering determinant 111 of Fig. 1, carries out the postfilter of filtering determination processing according to flow chart shown in Figure 29.So Figure 29 is the flow chart that the determination processing action of filtering determinant 111h is shown.Filtering determinant 111h, pixel value C, D satisfy the occasion of formula (1) in step 201, judge when the piece distortion takes place, and be used for allowing filter A112 carry out the signal of Filtering Processing with regard to output, and carry out Filtering Processing by filter A112 in step 203.On the other hand, pixel value C, D do not satisfy the occasion of formula (1) in step 201, judge the piece distortion does not take place, and just can't help filter A112 to carry out Filtering Processing.
In other words, flow chart shown in Figure 29 is the flow chart that has omitted step 202 in flow chart shown in Figure 4.In the Filtering Processing of step 203, use the formula (19) of using pixel value C and pixel value D.
Y＝(C+D)/2......(19)
The interpolation processing of utilizing formula (19) as shown in figure 30.
Like this, the occasion of the Filtering Processing of carrying out at each 1 pixel value by block boundary can realize that also determination processing is succinct, and computing is rapid, and the piece distortion reduces.In other words, change and cut down the occasion of power consumption on a small scale, preferably adopt this postfilter of this example at the strong request circuit scale.
In addition, postfilter shown in Figure 28, as shown in Figure 7, it constitutes also can select from the output of filter A112 or any one of decoding video signals 115.In addition, in this example, explanation be the occasion that in step 201, adopts threshold k, but also can adopt Th_i, Th_k, quantization parameter Qp as threshold value.
Example 10
In example 9, the occasion of each 1 pixel of the front and back of using block boundary being implemented the judgement of piece distortion illustrated, in this example, the occasion of each 3 pixel of the front and back of using block boundary being implemented the judgement of pieces distortion is illustrated.
Consider each 3 pixel value A, B, C, D, E, F that pixel is Figure 31 of block boundary.And the configuration example of postfilter 109 is shown in Figure 32.Postfilter shown in Figure 32 is in the filtering determinant 111 of Fig. 1, carries out the postfilter of filtering determination processing according to flow chart shown in Figure 33.So Figure 33 is the flow chart that the determination processing action of filtering determinant 111i is shown.
Filtering determinant 111i, pixel value C, D satisfy the occasion of formula (1) in step 201, regard the difference between this block boundary pixel value C, D as the piece distortion.So, among filter A112, filter B113, filter C116 are some, carry out Filtering Processing.On the other hand, pixel value C, D do not satisfy the occasion of formula (1) in step 201, judge the piece distortion does not take place, and just do not carry out Filtering Processing.And the occasion of piece distortion judge to take place in step 201, and just enter into step 206, according to each the relation of formula (20) to pixel value A, B and C, and each the relation of pixel value D, E, F is judged.
| A-B|＜L and | B-C|＜L and | A-C|＜L
And | D-E|＜L and | E-F|＜L and | D-F|＜L...... (20)
Because satisfy the occasion of formula (20) in judgement, can think from pixel a to pixel c, and the distortion of the piece from pixel d to pixel f exists, just enter into step 207, according to formula (21) decision pixel value B, C, D and E.
Y＝|A-F|/5×x+(A+F)/2......(21)
Pixel value B, C, D and E according to formula (21) decision shown in Figure 34.In addition, the Y in the formula (21) is corresponding to new pixel value.Promptly be with Figure 34 in B1, C1, D1, E1 corresponding, Y=B1 during x=-1.5; Y=C1 during x=-0.5; Y=D1 during x=0.5; And Y=E1 during x=1.5.
In step 206, the occasion not satisfying formula (21) enters into step 202, and according to the relation of formula (3) to pixel value B, C, and the relation of pixel value D, E is judged.
Because satisfy the occasion of formula (3) in judgement, can think that the piece distortion that pixel b, c and pixel d, e produce exists, just enter into step 203, according to formula (4) decision pixel value C, D.
Because in step 202, in the occasion that does not satisfy formula (3), can think that the piece distortion only is present among pixel C and the pixel D, just enter into step 205, according to formula (19) decision pixel value C, D.
Like this, carry out the occasion of Filtering Processing in each 3 pixel of the front and back that utilize block boundary, because can be corresponding with a lot of phenomenons, the erroneous judgement of piece distortion reduces, and, owing to can handle 3 kinds of Filtering Processing, can obtain high quality images.In other words, in the occasion of the special high image quality of strong request, preferably adopt this postfilter of this example.
In addition, postfilter shown in Figure 32, as shown in Figure 7, it constitutes the output that also can select from filter A112, some from the output of filter B113 or decoding video signals 115.
In addition, in this example, explanation be the occasion that in step 201, adopts threshold k, but also can adopt Th_i, Th_k, quantization parameter Qp as threshold value.
In addition, explanation be in step 203,207, to carry out the occasion that linear interpolation is handled, but also can carry out the level and smooth interpolation processing of explanation in example 2.
More than example of the present invention has been carried out detailed announcement and description, but above description is a illustration that can applicable situation of the present invention, the present invention is not limited thereto.In other words, in not departing from the scope of the present invention, can consider that described situation is had all corrections and variation.
Postfilter of the present invention,
Be to be disposed at the signal that after will being vision signal decoding after unit carries out encoding process, obtains postfilter as the back level of the decoding circuit of decoding video signals output with the piece,
N-1 piece and N piece of comprising in the above-mentioned decoding video signals clip the borderline phase adjacency,
To be positioned at the piece of this mat woven of fine bamboo strips N-1, the pixel amplitude of the pixel c of close this block boundary is set at C; Will be on the certain orientation be set at B with the pixel amplitude of this pixel c pixel adjacent b; To be set at A with the pixel amplitude of this pixel b pixel adjacent a;
To be positioned at this N piece, be set at D at the pixel amplitude that clips above-mentioned border and above-mentioned pixel c pixel adjacent d along above-mentioned certain orientation; To be set at E with the pixel amplitude of this pixel d pixel adjacent e; In the time of will being set at F with the pixel amplitude of this pixel e pixel adjacent f;
Its formation comprises at least according to above-mentioned pixel amplitude C and D, and whether decidable the piece distortion takes place and with the filtering determinant of this result of determination output on above-mentioned block boundary;
When receiving the above-mentioned result of determination that the piece distortion takes place in above-mentioned block boundary, carry out to the Filtering Processing of above-mentioned decoding picture signal and with the filter of this result according to above-mentioned pixel amplitude C and D at least as display video signal output.Thus, can adopt complex calculations just can carry out postfilter handles.And,, also can obtain the effect of cutting down power consumption and dwindling circuit scale because such computing is simplified.
Claims (10)
1. postfilter is to be disposed to be decoding video signal after unit carries out encoding process with the piece, and the postfilter of the back level of the decoding circuit exported as decoded video signal of the signal that will decode, it is characterized in that:
Have judgement and in block boundary, produce the determinant of piece distortion,
To clip block boundary adjacent when being contained in N-1 piece in the above-mentioned decoded video signal and N piece, be positioned at this N-1 piece, the pixel amplitude of the pixel c of close this block boundary is C, be positioned at this N piece, the pixel amplitude that clips the adjacent pixel d of above-mentioned block boundary and above-mentioned pixel c is D, on the extended line that connects above-mentioned pixel c and above-mentioned pixel d, adjacent with above-mentioned pixel c, the pixel amplitude of pixel b that is positioned at the piece of above-mentioned N-1 is B, adjacent with above-mentioned pixel d, when the pixel amplitude that is positioned at the pixel e of above-mentioned N piece is E
The position of the above-mentioned block boundary on above-mentioned extended line makes x=0, make x＞0 in above-mentioned N the piece, make x＜0 in above-mentioned N-1 the piece, and working as with the pixel is under the situation of unit, the position of pixel b is that the position of x=-1.5, pixel c is that the position of x=0.5, pixel d is x=0.5, when the position of pixel e is x=1.5
When being judged as under the situation that produces the piece distortion on the above-mentioned block boundary, according to following formula the pixel amplitude of above-mentioned pixel b, c, d, e is modified to Y,
Y＝α1-β·γ
λx (x＞0)……(1)
Y＝α2+β·γ
λx (x＜0)……(2)
Wherein, α 1, α 2, β are the real numbers that satisfies α 1-α 2=2 β, and γ, λ are the constants of being scheduled to.
2. the described postfilter of claim 1 is characterized in that:
α 1 and α 2 are that β is the value by above-mentioned pixel amplitude B, E decision by the value of above-mentioned pixel amplitude B, C, D, E decision.
3. the described postfilter of claim 1 is characterized in that:
α 1, α 2, β are the values that is decided by following formula.
β＝B-E……(5)
4. the described postfilter of claim 1 is characterized in that:
γ is natural logrithm e, or 2.
5. the described postfilter of claim 4 is characterized in that:
λ more than or equal to 0.01 smaller or equal to 0.1.
6. postfilter processing method, be to be decoding video signal after unit carries out encoding process with the piece, and the postfilter processing method of carrying out after the decoding step exported as decoded video signal of the signal that will decode, it is characterized in that:
Have judgement and in block boundary, produce the determination step of piece distortion,
To clip block boundary adjacent when being contained in N-1 piece in the above-mentioned decoded video signal and N piece, be positioned at this N-1 piece, the pixel amplitude of the pixel c of close this block boundary is C, be positioned at this N piece, the pixel amplitude that clips the adjacent pixel d of above-mentioned block boundary and above-mentioned pixel c is D, on the extended line that connects above-mentioned pixel c and above-mentioned pixel d, adjacent with above-mentioned pixel c, the pixel amplitude of pixel b that is positioned at the piece of above-mentioned N-1 is B, adjacent with above-mentioned pixel d, when the pixel amplitude that is positioned at the pixel e of above-mentioned N piece is E
The position of the above-mentioned block boundary on above-mentioned extended line makes x=0, make x＞0 in above-mentioned N the piece, make x＜0 in above-mentioned N-1 the piece, and working as with the pixel is under the situation of unit, the position of pixel b is that the position of x=-1.5, pixel c is that the position of x=-0.5, pixel d is x=0.5, when the position of pixel e is x=1.5
When being judged as under the situation that produces the piece distortion on the above-mentioned block boundary, according to following formula the pixel amplitude of above-mentioned pixel b, c, d, e is modified to Y,
Y＝α1-β·γ
λx (x＞0)……(1)
Y＝α2+β·γ
λx (x＜0)……(2)
Wherein, α 1, α 2, β are the real numbers that satisfies α 1-α 2=2 β, and γ, λ are the constants of being scheduled to.
7. the described postfilter processing method of claim 6 is characterized in that:
α 1 and α 2 are that β is the value by above-mentioned pixel amplitude B, E decision by the value of above-mentioned pixel amplitude B, C, D, E decision.
8. the described postfilter processing method of claim 6 is characterized in that:
γ is natural logrithm e, or 2.
9. the postfilter processing method described in the claim 8 is characterized in that:
λ more than or equal to 0.01 smaller or equal to 0.1.
10. video signal decoding apparatus is characterized in that: have the postfilter described in the claim 1, and decoding circuit.
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| JP5490404B2 (en) * | 2008-12-25 | 2014-05-14 | シャープ株式会社 | Image decoding device |
| CN101841645B (en) * | 2010-05-10 | 2011-08-24 | 艾诺通信系统（苏州）有限责任公司 | Method for removing block effect of video image |
| US8805100B2 (en) | 2010-06-03 | 2014-08-12 | Sharp Kabushiki Kaisha | Filter device, image decoding device, image encoding device, and filter parameter data structure |
| JP5741092B2 (en) * | 2011-03-15 | 2015-07-01 | 富士通株式会社 | Image encoding method and image encoding apparatus |
| JP6964780B2 (en) * | 2017-12-29 | 2021-11-10 | テレフオンアクチーボラゲット エルエム エリクソン（パブル） | How to code and / or decode video using the reference value and the associated device |
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