Europdisches
`Patentamt
`
`
`
`
`
`European
`Patent Office
`
`
`
`
`Office européen
`
`des brevets
`
`
`
`
`
`uu S
`
`9d
`
`yygsneenna4
`
`/
`
`?
`
`
`
`
`
`Les documentsfixés a
`The attached documents
`
`
`
`
`
`
`
`
`
`
`
`
`
`cette attestation sont
`are exact copies of the
`
`European patent application conformes 4 la version
`
`
`
`
`
`
`
`
`
`
`
`described on the following
`_initialernent déposée de
`
`
`
`
`
`
`
`
`page, as originally filed.
`la demande de brevet
`européen spécifiée aia
`
`
`
`page suivante.
`
`
`
`
`
`Bescheinigung
`
`
`
`Certificate
`
`
`
`Attestation
`
`
`
`Die angehefteten Unteria-
`
`
`gen stimmen mit der
`
`
`
`
`urspriinglich eingereichten
`
`
`
`
`
`
`Fassung der auf dem nach-
`sten Btatt bezeichneten
`
`
`
`europaischen Patentanmel-
`
`dung Uberein.
`
`
`
`
`Patentanmeldung Nr.
`
`
`
`
`
`
`
`
`
`Patentapplication No. Demande de brevet n°
`
`
`
`00402939. 3
`
`
`
`Der Pradsident des Europdischen Patentamts;
`
`
`
`
`Im Auftrag
`
`
`For the President of the European Patent Office
`
`
`
`
`
`
`
`Le Président de Office européen des brevets
`
`
`
`
`
`
`p.o.
`
`
`
`
`
`
`
`
`
`LLC. HATTEN-HECKMAN
`
`
`
`
`
`DEN HAAG, DEN
`
`
`THE HAGUE,
`
`
`LA HAYE,LE
`
`
`16/07/01
`
`
`
`EPA/EPO/OEB Form
`
`
`
`
`1014
`
`
`
`
`
`ni esLiarconetiont
`
`ee
`eereeeeereens
`
`Page 1 of 22
`
`GOOGLEEXHIBIT 1015
`
`Page 1 of 22
`
`GOOGLE EXHIBIT 1015
`
`

`

`
`
`
`THIS PAGE BLANK(sro)
`
`
`Page 2 of 22
`
`Page 2 of 22
`
`

`

`-
`
`0)
`
`
`
`Europalisches
`
`
`Patentamt
`
`
`
`European
`
`
`Patent Office
`
`
`
`
`
`
`Office européen
`
`
`
`des brevets
`
`
`
`
`Blatt 2 der Bescheinigung
`
`
`
`
`
`Sheet 2 of the certificate
`
`
`
`
`
`Page 2 de I’attestation
`
`
`
`Anmeldung Nr.:
`
`
`
`
`
`Application no.:
`
`
`Demande n*:
`
`
`Anmelder,
`
`Applicant{s}:
`
`Demandeur(s):
`
`Koninklijke Philips Electronics N,V.
`
`
`
`5621 BA Etndhoven
`
`
`
`NETHERLANDS
`
`00402939.3
`
`
`
`Anmeldetag:
`
`
`Date of filing:
`
`Date de dépot:
`
`
`
`
`
`/
`
`
`
`24/10/00
`
`
`
`
`
`Rew
`
`mene
`
`
`
`Bezeichnung der Erfindung:
`Title of the invention:
`
`
`
`
`
`
`Titre de invention:
`
`
`
`
`
`
`
`
`
`
`Method of transcading and transcoding device with embedded filters
`
`
`
`
`
`
`In Anspruch genommenePrioridtien) / Priority{ies) claimed / Priorité(s} revendiquée(s)
`
`
`
`
`
`
`
`
`Staat:
`Tag:
`Aktenzeichen:
`
`
`
`State:
`File no.
`Date:
`
`
`
`Numéro de dépét:
`Data:
`Pays:
`
`
`
`
`
`
`
`
`
`Internationale Patentklassifikation:
`
`
`international Patent classification:
`Classification internationate des brevets:
`
`
`
`
`
`
`4
`
`
`
`
`Am Anmeideiag benannte Vertragstaaten:
`
`
`
`
`Contracting states designated at date of filing: AT/BEACH/CY/DE/DK/ES/FIVFR/GB/GRAIE/AT/LIVLUSMC/NLPTAS E/T
`
`
`
`
`
`
`
`Etats contractants désignés lors du depét:
`
`
`
`
`
`
`Bemarkungen:
`Remarks:
`
`Remarques:
`
`
`
`
`
`
`
`
`
`
`EPA/EPO/OEB Form
`
`
`
`
`1012
`
`
`
`- 11.00
`
`
`
`
`wm Eee ween ne
`— = tent
`Page 3 of 2
`
`Zt Teteereeememennewibaieden eras petermanermmetmemmememreee we me Fee lit te pee
`
`
`metm ee sree held, cemties
`
`Page 3 of 22
`
`

`

`
`
`
`THIS PAGE BLANK wsrto;
`
`
`Page 4 of 22
`
`Page 4 of 22
`
`

`

`2ANO-2000
`
`OOZO2G3OR3(22102000)
`
`DESE
`
`
`
`
`
`
`
`
`
`Method of transcoding and transcoding device with embedded filters
`
`
`
`
`
`
`
`
`
`
`FIELD OF THE INVENTION
`
`
`
`
`
`
`
`
`
`
`
`The present invention relates to a method of transcoding a primary encoded signal
`
`
`
`
`
`
`
`
`
`
`
`comprising a sequence of pictures, into a secondary encoded signal, said method of
`
`
`
`
`
`
`
`
`
`
`
`
`
`transcoding comprising at least a step of decoding a current picture of the primary encoded
`
`
`
`
`
`
`
`
`
`
`
`
`
`signal for providing a first transformed signal, an encoding step, following the decoding step,
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`for obtaining the secondary encoded signal, and a step of predicting a transformed motion
`
`
`
`
`
`
`
`
`
`
`
`compensated signal from a transformed encoding error derived from the encoding step, said
`
`
`
`
`
`
`
`
`
`
`
`
`
`prediction step being located between the encoding and decoding steps. The invention afso
`
`
`
`
`
`
`
`
`
`
`
`
`relates to a corresponding device for carrying out such a method of transcoding.
`
`
`
`
`
`
`
`
`
`
`
`This invention is particularly relevant for the transcoding of MPEG encoded video
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`NomaceaseONTt
`
`
`
`
`
`10
`
`
`
`15
`
`
`
`20
`
`
`
`
`
`30
`
`
`
`35
`
`
`
`signais.
`
`
`
`
`
`
`BACKGROUND OF THE INVENTION
`
`
`
`
`
`
`
`
`
`
`Bit-rate transcoding is a technique which allows a primary video stream encoded at
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`a bit-rate BR1 to be converted into a secondary video stream encoded at a bit-rate BR2
`
`
`
`
`
`
`
`
`
`
`
`
`
`tower than 8R1, the bit-rate reduction being performed in order to meet requirements
`
`
`
`
`
`
`
`
`
`
`
`
`imposed by the means of transport during broadcasting. A transcoding device as described
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`in the opening paragraphis disclosed in the European Patent Application n° EP 0690 392
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`(PHF 94001) and is depicted in Fig. 1. Said device (100) for transcoding encoded digital
`
`
`
`
`
`
`
`
`
`
`
`
`signals ($1) which are representative of a sequence of images, comprises a decoding
`
`
`
`
`
`
`
`
`
`
`
`
`channei (11,12) followed by an encoding channel (13,14,15). A prediction channelis
`
`
`
`
`
`
`
`
`
`
`
`connected in cascade between these two channels, and said prediction channel comprises,
`
`
`
`
`
`
`
`
`
`
`
`in series, between two subtractors (101,102), an inverse discrete cosine transform sub-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`assembly IDCT (16), a picture memory MEM (17), a circuit MC (18) for motion compensation
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`in view of displacement vectors (Vv) which are representative of the motion of each image,
`
`
`
`
`
`
`
`
`and a discrete cosine transform sub-assembly DCT (19).
`
`
`
`
`
`
`
`
`
`/
`
`
`
`
`
`
`SUMMARYOF THE INVENTION
`
`
`
`
`
`
`
`
`
`
`
`
`
`It is an object of the invention to provide a method of transcoding and a
`
`
`
`
`
`
`
`
`
`
`
`
`corresponding device that allows a better quality of pictures for low bit-rate applications. The
`
`
`
`
`
`
`
`
`present invention takes the following aspect into consideration.
`
`
`
`
`
`
`
`
`
`
`
`With the advent of homedigital video recording of MPEG broadcasts, transcoders
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`can be used in consumer devices to implement long play modes or to guarantee the
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`recording time. However, the input signal to be transcoded has often been encoded at a
`
`
`
`
`
`
`
`
`
`Printack16-07-2001
`
`Page 5 of 22
`
`Page 5 of 22
`
`

`

`a
`
`-
`
`t
`
`‘
`
`
`
`
`
`(0402939a(2amOrAO00)
`
`
`
`
`
`2
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`variable bit-rate with a low averagebit-rate. This is due to the generalisation ofstatistical
`multiplexing that allows broadcasters to put a lot of video programs in a multiplex in order to
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`save the bandwidth. Itis likely that a coarser re-quantisation of the input signal, using a
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`method of transcoding according to the priorart, will lead to conspicuous quantisation
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`artefacts. As a consequence, such a transcoding method is not adapted for low bit-rate
`
`
`
`
`
`
`
`applications.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`To overcome this drawback, the method of transcoding in accordance with the
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`invention is characterised in that it comprises a filtering step, between the decoding and
`
`
`
`
`
`
`
`
`
`
`
`encoding steps, for providing a filtered transformed signal, and the prediction step further
`
`
`
`
`
`
`10
`
`
`
`
`comprises :
`
`-
`
`-
`
`
`
`
`
`
`
`
`
`
`
`
`an adding sub-step for determining a sum of the transformed motion compensated
`
`
`
`
`
`
`
`-signal and a transformed signal, and
`
`
`
`.
`
`
`
`
`
`
`
`
`
`
`
`
`a Subtracting sub-step for determining the transformed encoding error from a difference
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`between said sum and a second transformed signal provided by the encoding step.
`
`
`
`
`
`
`
`
`
`
`
`The transcoding method in accordance with the invention allows to implementfilters
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`in the transcoder of the prior art at a negligible cost. Those filters can be tuned to controi
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`the static and dynamic resolution and also to perform noise reduction. For the same. number
`
`
`
`
`
`
`
`
`
`
`
`
`
`of bits, the filtered transformed signal is encoded with a smaller quantisation scale thus
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`reducing visuai artefacts such as blocking, ringing and mosquito noise.
`
`
`
`
`
`
`
`
`
`
`
`
`In a first embodiment of the invention, the adding sub-step is intended to provide
`
`
`
`
`
`
`
`
`
`
`
`
`
`the sum of the transformed motion compensated signal and the first transformed signal, and
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`the filtering step is a temporalfiltering step for receiving said sum and for providing the
`
`
`
`filtered transformed signal to the encoding step. Such a temporalfiltering step allows to
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`perform noise reduction using, for example, a recursive filter. As a consequence, bits are
`
`
`
`
`
`
`
`
`
`
`
`
`
`only spent on the useful information and the picture quality is thus increased.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`In another embodiment of the invention, the filtering step is a spatial fittering step
`
`for receiving the first transformed signal, and the adding sub-step is intended to provide the
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`sum of the transformed motion compensated signal and the filtered transformed signal to
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`the encoding step. Such a spatial filtering allows a reduction of the sharpness of the picture
`
`
`
`
`
`
`
`
`
`
`and decreases the possible source of ringing and mosquito noise.
`The present invention also relates to a corresponding device for carrying out such a
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`method of transcoding.
`
`
`
`
`
`
`
`
`
`
`
`The present inventionfinally relates to a computer program product for a receiver,
`such as a digital video recorder or a set-top-box, that comprises a set of instructions, which,
`
`
`
`
`
`
`
`
`
`
`
`
`
`when loaded into the receiver causes the receiver to carry out the method of transceding.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`These and other aspects of the invention will be apparent from and will be
`
`
`
`
`
`
`
`
`elucidated with reference to the embodiments described hereinafter.
`
`is
`
`
`
`20
`
`
`
`
`
`30
`
`
`
`35
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`OOee
`
`i scemanesenediesamaeEeeehern eeeden oe eeseeel eReeee nome
`
`
`
`
`
`
`Page 6 of 22
`
`Page 6 of 22
`
`

`

`ZAM1O-BOOO
`
`OO40293983(2451102000)
`
`DESE
`
`
`
`
`
`
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`The present invention will now be described in more detail, by way of example, with
`
`
`
`
`
`
`reference to the accompanying drawings, wherein :
`
`
`
`
`
`
`
`
`
`
`
`
`
`Fig. 1 is a block diagram corresponding to a transcoding device according to the prior
`
`
`
`
`
`
`
`
`-
`
`art,
`
`
`
`
`
`10
`
`
`
`
`
`
`
`nhTae?ORRA
`
`
`
`15
`
`
`
`20
`
`-
`
`-
`
`-
`
`
`
`
`
`
`
`
`
`
`
`
`Fig. 2 is a block diagram corresponding to a first embodimentof a transcoding device
`
`
`
`
`
`
`
`
`
`
`according to the invention, said device comprising a temporalfilter,
`
`
`
`
`
`
`
`
`
`
`
`
`Fig. 3 is a block diagram corresponding to a second embodiment of a transcoding device
`
`
`
`
`
`
`
`
`
`
`
`according tc the invention, said device comprising a spatial filter, and
`
`
`
`
`
`
`
`
`
`
`
`
`Fig. 4a block diagram corresponding to a third embediment of a transcoding device
`
`
`
`
`
`
`
`
`
`
`
`according to the invention, said device also comprising a spatial filter.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`DETAILED DESCRIPTION OF THE INVENTION
`
`
`
`
`
`
`
`
`
`
`
`
`The present invention relates to an improved method of and a corresponding device
`
`
`
`
`
`
`
`
`
`
`
`
`for transcoding video encoded signals. It relates, more especially, to MPEG-2 encoded
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`signals but it will be apparent to a person skilled in the art that said method of transcoding
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`stays also applicable to any type of video signals encoded using a block-based technique
`
`
`
`
`
`
`
`
`
`
`
`
`
`such as, for example, those provided by MPEG-1, MPEG-4, H-261 or H-263 standards.
`
`
`
`
`
`
`
`
`
`
`
`
`A transcoding device allows a primary encoded signal ($1) previously encoded with a
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`first quantisation scale and comprising a sequence of pictures, to be converted into a
`
`
`
`
`
`
`
`
`
`
`secondary encoded signal ($2) encoded with a second quantisation scale.
`
`
`
`
`
`
`
`
`
`
`Such a transcoding device comprises at least the following elements :
`
`
`
`
`
`
`
`
`
`
`
`
`~ adecoding sub-assembly comprising a variable tength decoder VLD andafirst
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`25
`dequantiser IQ for decoding a current picture of the primary encoded signal and for
`
`
`
`
`
`providing a first transformed signal,
`
`
`
`
`
`
`
`
`
`
`
`
`an encoding sub-assembly comprising a quantiser Q, a variable length encoder VLC for
`
`
`
`
`
`
`
`
`
`
`obtaining the secondary encoded signal, and a second dequantiser IQ,
`
`
`
`
`
`
`
`
`
`
`a prediction sub-assembly, between the encoding sub-assembly and the decoding sub-
`
`
`
`
`
`assembly, and comprising in series :
`
`
`
`
`
`
`
`
`
`
`
`ean inverse discrete transform sub-assembly IDCT (an Inverse Discrete Cosine
`
`
`
`
`
`
`Transform in the case of MPEG),
`
`
`
`
`a picture memory MEM,
`
`
`
`
`
`
`
`
`
`
`
`
`acircuit MC for motion compensation in view of displacement vectors which are
`
`
`
`
`
`
`
`representative of the motion of each picture,
`
`
`
`
`
`
`
`-
`
`-
`
`
`*
`
`¢
`
`
`
`30
`
`
`
`35
`
`BretonOreo,
`
`Page 7 of 22
`
`Page 7 of 22
`
`

`

`
`
`(24-10-2000)
`
`
`
`
`
`
`
`
`
`
`
`*
`
`
`
`
`
`
`
`
`
`
`a discrete transform sub-assembly DCT for predicting a transformed motion
`
`
`
`
`
`
`
`
`
`
`
`
`
`compensated signal (Rmc) from a transformed encoding error (Re) derived from the
`
`
`
`
`encoding sub-assembly,
`
`
`
`
`
`
`*®
`
`
`e
`
`
`
`
`
`
`
`
`
`
`
`
`
`an adder for determining a sum of the transformed motion compensated signal and
`
`
`
`a transformed signal,
`
`
`
`
`
`
`
`
`
`
`
`
`a subtracter for determining the transformed encoding errer from a difference
`
`
`
`
`
`
`
`
`
`
`
`
`between said sum and a second transformed signal (R2)} provided by the encoding
`
`
`sub-assembly,
`
`
`
`-
`
`
`
`
`
`
`
`
`
`
`
`a filter, between the decoding sub-assembly and the encoding sub-assembly, for
`
`
`
`10
`
`
`
`
`
`
`
`
`providing a filtered transformed signal(Rf).
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Said filter can be a temporal or a spatialfilter intended to control the static and
`
`
`
`
`
`
`
`
`
`
`
`dynamic resolution and-to perform noise reduction ona picture. The different
`
`
`
`
`
`
`
`
`
`
`
`
`
`implementations of such filters are described in the fallowing Figs. 2 to 4.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`In a first embodimentof the invention, the transcoder implements a motion
`
`
`
`
`
`
`
`
`
`
`
`compensated temporal filter. Temporal filtering allows to reduce signals which are not
`
`
`
`
`
`
`
`
`
`
`
`
`
`correlated from frame to frame. It can very effectively reduce noise when combined with
`
`
`
`
`
`
`
`
`
`
`
`motion compensation, as mation compensation tries to correlate the image content from
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`frame to frame. In this embodiment, a recursive filter is implemented since it provides a
`
`
`
`
`
`better selectivity at lower cost.
`
`
`
`
`
`
`
`
`
`A naive transcoding chain with a motion compensated recursive temporalfilter
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`15
`
`
`
`20
`
`
`
`
`
`30
`
`
`
`35
`
`
`
`-
`
`-
`-
`
`-
`
`-
`
`-
`-
`
`
`
`
`usually comprises in cascade :
`
`
`
`
`
`
`
`
`
`
`
`
`a decoder for providing motion compensated blocks D1 of decoded pictures from an
`
`
`input stream,
`a recursive temporalfilter for providing filtered blocks Df of decoded pictures, and
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`an encoder for providing an output stream and motion compensated blocks D2 of locally
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`decoded pictures after encoding.
`
`
`
`
`
`
`
`
`
`
`
`
`To reduce costs, the motion compensation in the encoderis re-used in the recursive
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`temporalfilter. Thus, the signal D2 is fed back to said filter instead of Df. The fiitering
`
`equation of a motion compensated block Df(n,m)is then :
`
`
`
`
`
`
`
`Df(n,m) = (1 — «)-D1(n,m) + « -MC(02Ap(n)), Vin,m)),
`
`
`
`
`
`
`where :
`
`
`
`
`
`
`
`nis the index of the current picture,
`
`
`
`
`
`
`
`
`
`- mis the index of a block of said current picture,
`
`
`
`
`
`
`
`
`
`
` Vin,m) is the motion associated with block m, of picture n,
`
`
`
`
`
`
`
`
`
`
`
`p(n) is the index of the anchorpicture associated with image n,
`
`
`
`
`
`
`
`MC is the motion compensation operator, and
`
`
`
`
`
`
`
`(4)
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Page 8 of 22
`
`wi ne
`
`
`He ee
`
`
`
`
`OR Ae eu racemeimteeemmetreies mn eee ee
`
`
`
`
`
`toa
`
`
`
`bere
`
`=~
`
`
`Page 8 of 22
`
`

`

`Bi 022000)
`
`.
`
`(00402939%3(2451022000)
`
`
`
`5
`
`
`
`
`
`
`
`
`
`
`
`s
`
`
`
`10
`
`
`
`15
`
`
`
`20
`
`
`
`
`
`
`
`
`
`
`
`
`
`~
`ais a positive scalar smaller than one that tunes the filter response.
`
`
`
`
`
`
`
`
`
`
`
`An expression similar to equation (1) can be drawnfor bi-directional motion
`
`
`
`
`
`
`
`
`
`
`
`compensation. However, without loss of generality, we shall restrict the demonstration to
`
`
`
`
`
`
`
`
`
`
`
`
`
`the unidirectional case. Note that intra encoded blocks cannot be filtered since no prediction
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`is formed for them. Yet, intwa encoded blocks in non intra pictures correspond most often to
`
`
`
`
`
`
`
`
`
`
`newly exposed regions that could not possibly be temporally filtered.
`
`
`
`
`
`
`
`
`
`
`
`
`The naive transcoding chain can be simplified using the hypothesis that the motion
`
`
`
`
`
`
`
`
`
`
`
`compensation information is unchanged. To this end, the motion compensated block
`
`
`
`
`
`Di(n,m) is expressed as follows :
`
`
`
`
`Di(n,m) = Mt .R1fn,m)-M+McC(O1(p(n)), vin, m)),
`
`where :
`
`
`
`
`
`
`
`
`“
`M is the 8 x & discrete cosine transform matrix,
`
`
`
`
`
`
`
`- Mis the corresponding transposed matrix, and
`
`
`
`
`
`
`
`
`
`
`
`Ri(n,m)is the residue retrieved from the input bit-stream after variable length
`
`
`
`
`
`decoding VLC and dequantisation 1Q,
`
`
`
`
`
`
`
`
`
`
`
`
`M is defined by equation (3) and is such that MM’ =I:
`
`M “(2h
`
`
`
`
`
`
`
`
`
`1 leostix (2)+1)/16)/2 otherwise.
`
`
`
`
`
`
`
`
`
`
`Then, the filtered block is encoded using the same motion compensation
`
`
`
`
`
`
`
`information. Let Rf(n,m) be the corresponding residue :
`
`
`
`
`
`
`(4)
`Rf(n,m)} = M-Df(n,m)- Mt —M-MC(O2(p(n)), Vin, m))- MF.
`
`
`
`
`
`
`
`
`
`
`
`
`The residue is then quantised and dequantised again to compute the locally decoded
`
`
`
`
`
`
`
`
`
`
`pictures D2. Let R2(n,m) be the quantised and dequantised residue :
`
`
`(5)
`R2(n,m) = M-D2(n,m). Mt —M-MC(O2(p(n)), V(n,m))- mM".
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`The equations (1) and (4) are combined so that Rf is derived directly from D1 and
`
`
`
`
`
`
`
`
`
`
`
`(2)
`
`
`
`
`
`
`
`(3)
`
`
`
`
`
`
`
`
`
`
`
`-
`
`ifi=0,
`
`
`
`
`
`
`
`
`
`
`25
`
`
`
`D2:
`
`Rf(n,m) = (1 - a) [M-D1{n,m)- Mt -— M-Mc(O2(p(n)),Vin,m))-M° }.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Combining the equation (2) with equation (6) gives :
`
`
`
`
`
`
`Rf(n,m) = (1 - a} [ Ri{n,m)+M -MC(D1(p(n)}, Vin,m))- mt
`-M.MC{02(p(n)), v(n,m))- m*|.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Since motion compensation is performed identically from D1 and from D2, the
`
`
`
`
`
`
`
`
`
`
`
`
`
`motion compensation operator MC can operate on the picture difference,i.e., on the error
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`signal due to the transcoding operation. Defining 85D = D1 - D2, equation (7) is rewritten as
`
`follows :
`
`
`
`(6)
`
`
`
`(7)
`
`
`
`
`
`
`
`
`
`
`
`
`
`30
`
`Printeck16-07-2001
`
`Page 9 of 22
`
`Page 9 of 22
`
`

`

`
`
`
`
`
`
`
`
`
`(8)
`RF(n,m) = (t - 2) [Rif,m)+M-MC(SD{p(n)), V(a,m))-M¢}.
`
`
`
`
`
`
`
`The error signal 8D can be derived from the prediction errors, combining equations
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`(5) and (6):
`
`
`
`&D{n,m)= m|Sten)—R2{(n,m)-M,
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Equations (8) and (9) define the transcoder structure depicted in Fig. 2. Said
`
`
`
`transcoder (200) comprises :
`
`
`
`
`
`(9)
`
`
`
`-
`
`-
`
`-
`
`
`
`
`
`
`
`
`
`
`
`
`a decoding channel comprising a variable length decoder VLD (11) and a first
`
`
`
`
`
`
`
`
`
`
`
`
`dequantiser IQ (12) for decoding a current picture of a primary encoded signal ($1) and
`
`
`
`
`
`for providing a first transformed signal (R1),
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`an encoding channel comprising a quantiser Q (13), a variable length encoder VLC (14)
`
`
`
`for obtaining the secondary encoded signal ($2), and a second dequantiser IQ (15)for
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`providing a second transformed signal (R2),
`
`
`
`
`
`
` @ prediction channel comprising, in series :
`
`
`
`
`«
`
`
`
`
`
`
`
`
`
`
`
`a subtractor (201) for determining a transformed encoding error (Re) and whose
`
`
`
`
`
`
`
`
`
`negative input receives the second transformed signal,
`
`
`
`
`e
`
`*
`
`
`e
`
`
`*
`
`
`
`
`
`
`
`aninverse discrete cosine transform IDCT (16),
`
`
`
`
`a picture memory MEM (17),
`
`
`
`
`
`
`acircuit MC (18) for motion compensation,
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`a discrete cosine transform DCT (19) for predicting a transformed motion
`
`
`
`
`
`compensated signal (Rmc),
`
`
`
`
`
`10
`
`
`
`15
`
`
`
`20
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`an adder (202) for providing a sum of the transformed motion compensated signal
`
`
`
`
`
`
`
`
`
`
`
`
`
`and thefirst transformed signal (R1) to the positive input of the subtractor,
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`a temporalfilter W (21) for receiving said sum and for providing the filtered transformed
`
`
`
`
`
`
`signal (Rf) to the quantiser Q (13).
`
`
`
`
`
`
`
`
`
`
`
`The strength of the motion compensated recursive temporalfilter can be adjusted
`
`
`
`
`
`
`
`
`
`
`
`
`separately for each transformed coefficient Rfi], i.e., for each DCT sub-band. The
`transformed coefficientof ranki is multiplied by W[i] = 1-afi] such as :
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`REL] = Wi] (R1fi] + Rmcfi})
`(10)
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Thus, the noise reduction can be tuned to the spectral shape of the noise. It can
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`also be decided not to filter low frequencies in order to avoid visible artefact in case of a bad
`
`
`
`
`
`
`motion compensation and to reduce the noise.
`
`
`*
`
`-
`
`25
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`In the second and third embodiments of the invention, the transcoder implements a
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`spatial filter. Spatial filtering is not so efficient to reduce the noise as motion compensated
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`temporal filtering is. Yet, it can prevent block artefacts at low bit-rate, smoothing down
`
`
`
`
`
`
`
`
`
`
`
`
`sharp edges that would otherwise create ringing effects. It can also simplify complex
`
`
`
`
`
`35
`
`
`
`
`
`Page 10 of 22
`
`
`
`
`
`
`
`Page 10 of 22
`
`

`

`
`
`
`
`OO40293083(24511022000)
`
`
`
`DESeE
`
`
`7
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`patterns that would be otherwise randomly distorted from one picture to the other, resuiting
`
`
`
`
`
`in the so-called mosquito noise.
`
`
`
`
`
`
`
`
`
`
`
`
`
`Let us consider again the naive transcoding chain. The pixei domain filter shall have
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`the same granularity that the granularity of the decoder. Thus we consider a block-wi
`fitter. Let Di(n,m) be biock m of picture n. The filtered block Di(n,m)is computed as
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`follows :
`
`
`
`
`
`
`
`
`Df(n,m) = Fv(n). D1(n, m)- Fh*(n)
`
`
`
`
`
`
`
`
`
`
`
`where Fy(n) and Fh({n) are matrices that define respectively the vertical and
`
`
`
`
`
`horizontal filtering within the block.
`
`
`
`
`
`
`
`
`
`
`Combining the equation (11) with the equation (2), we find :
`
`
`
`
`Df(n,m) = Fv{n)- Mt -R1(n,m)-M-Fh*(n)
`
`
`(12)
`+Fu(n}-MC(D1(p(n)), V(n, m))- Fat (n)
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`If the filter is the same for a group of pictures, then Fv(n) = Fy(p(n)) and Fhin) =
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Fh(p(n)}. Thus, the following approximation can be given for equation (12) based on the
`
`
`
`
`
`
`
`
`assumption that block-wise filtering commutes with motion compensation :
`
`
`
`
`
`
`
`Df(n,m) = Fv(n)- M* - Ri(n,m)-M-Fht(n}+ MC(DF(p{n)), V(n, m)}
`
`
`
`
`
`
`
`
`
`
`
`
`
`It follows that the block-wise filter can be applied to residue Ri(n,m) after an
`
`
`
`
`
`
`
`
`
`
`
`
`
`inverse discrete cosine transform IDCT. To implement the spatialfilter in the transcoder, the
`
`
`
`
`
`
`
`residue Ri(n,m) needs to be substituted by :
`
`
`
`
`
`
`Rf(n,m) = M-Fv{n)}- Mt -Ri(n,m)-M-Fh'(n)-M*
`
`
`
`
`
`
`
`
`
`
`Even if the matrices M.Fv(n)-M' and M-Fh'(n)-M" can be pre-computed,their
`
`
`
`
`
`
`
`
`
`
`
`
`
`computing seems to involve many operations. Said computing can be simplified for a class of
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`block-wise filters for which the two matrices are diagonal. Such filters are symmetric filters
`
`
`
`
`
`
`
`
`
`
`
`
`
`with an even number of taps. In our embodiment, we consider normalised 3-tap symmetric
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`filters since they are more suitable for small blocks. Such filters have a single parameter,
`
`
`
`
`
`
`
`
`
`
`
`
`denoted a. The corresponding pixel domainfiltering matrix, (F,oaj<a, is defined by :
`
`
`
`
`
`
`a
`fori=j—1tod,
`
`
`
`fi
`i
`fori=j+1,
`
`
`
`
`24+ali+a
`fori=j=Oand7,
`
`0
`otherwise.
`
`
`
`
`
`
`
`_
`
`
`
`
`“1
`
`
`
`
`
`
`
`
`
`\escaattenete,vee
`
`
`
`
`
`
`
`
`
`5
`
`
`
`10
`
`
`
`is
`
`
`
`20
`
`
`
`25
`
`
`
`(11)
`
`
`
`
`
`
`
`(13)
`
`
`
`
`
`
`
`(14)
`
`
`
`
`(15)
`
`
`
`
`
`
`
`Then,
`
`
`2cos(ix/8)+a
`—2
`M-B. mt =
`
`
`
`
`
`Wo
`24a lo
`
`
`
`
`
`fori=j
`otherwise.
`
`
`
`(16)
`
`
`
`
`
`intect16-07-2001
`
`Page 11 of 22
`
`Page 11 of 22
`
`

`

`2AOS2000
`
`Q040293983(2450-2000)
`
`
`8
`
`DESE
`
`-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Thus, to implement filtering with horizontal parameter a, and vertical parameter a,,
`
`
`
`
`
`
`
`
`
`
`
`
`the residue R1(n,m) needs to be weighted (component-wise) by (Wi,)oaj<s defined as
`
`follows :
`
`
`2costin/Bj+a,
`
`
`( /8)
`
`
`ve.
`
`
`(j /8)
`2cosijn/Sj+a
`
`
`
`
`
`h
`
`
`
`
`
`
`
`(17)
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`2+a,
`2+a,
`
`
`
`
`
`
`
`
`
`
`
`Fig. 3 shaws a transcoder with spatial pre-fittering according to the second
`
`
`
`
`
`
`
`
`embodiment of the invention. Said transcoder (300) comprises :
`
`
`
`
`
`
`
`
`
`
`
`
`
`- a decoding channel comprising a variable tength decoder VLD (11) andafirst
`
`
`
`
`
`
`
`
`
`
`
`dequantiser IQ (12) for providing a first transformed signal (R1),
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`a Spatial filter W (31) for receiving said first transformed signal and for providing the
`
`
`
`
`filtered transformed signal (Rf),
`
`
`
`
`
`
`
`
`
`
`
`
` an-enceding channel comprising a quantiserQ (13), a variable length encoder VLC (14)
`
`
`
`
`
`
`
`
`
`
`
`
`
`and a second dequantiser IQ (15) for providing a second transformed signal (R2},
`
`
`
`
`
`
`@ prediction channel! comprising, in series :
`
`
`
`
`
`
`
`
`
`
`
`
`®
`a subtractor (201) for determining a transformed encoding error (Re) and whose
`
`
`
`
`
`
`
`negative input receives the second transformed signal,
`
`
`
`
`
`
`
`an inverse discrete cosine transform IDCT (16),
`
`
`
`
`
`a picture memory MEM (17),
`
`
`
`
`
`
`a dreuit MC (18) for motion compensation,
`
`
`
`
`
`
`
`
`
`
`a discrete cosine transform DCT (19) for predicting a transformed motion
`
`
`
`
`compensated signal (Rmc), and
`
`
`
`
`
`
`
`
`
`
`
`
`an adder (302) for providing a sum of said transformed motion compensated signal
`
`
`
`
`
`
`
`
`
`
`
`
`
`and the filtered transformed signal (Rf) to the positive input of the subtractor.
`
`
`
`
`
`
`
`
`
`
`
`
`Fig. 4 is a transceder according to the third embodimentof the invention, with
`
`
`
`
`
`
`
`
`
`
`
`Spatial post-filtering whose weighting factors are W,;. Said transcoder (400) comprises :
`
`
`
`
`
`
`
`
`
`
`
`a decoding channel (11,12) for providing a first transformed signal (R1),
`-
`
`
`
`
`
`
`
`
`
`
`
`
`an encoding channel (13,14,15) further comprising an inverse filter (42) for providing a
`-
`
`
`
`
`second transformed signal (R2),
`
`
`
`
`
`
`a prediction channel comprising, in series :
`
`
`
`
`
`
`
`
`
`
`
`
`e
`a subtractor (201) for determining a transformed encoding error (Re) and whose
`
`
`
`
`
`
`
`negative input receives the second transformed signal,
`
`
`
`
`
`
`
`an inverse discrete cosine transform IDCT (16),
`
`
`
`
`
`a picture memory MEM (17},
`
`
`
`
`
`
`a circuit MC (18) for mation compensation,
`
`
`
`
`
`
`
`
`
`
`a discrete cosine transform DCT (19) for predicting a transformed motion
`
`
`
`compensated signal (Rmc),
`
`
`
`
`
`Why =
`
`
`
`
`5
`
`
`
`10
`
`
`
`15
`
`
`
`20
`
`
`
`25
`
`
`
`30
`
`
`
`35
`
`-
`
`-
`
`-
`
`-
`
`
`*
`
`*
`
`*
`
`®
`
`
`©
`
`
`*
`
`*
`
`©
`
`*
`
`Printack16-07-2001
`
`Page 12 of 22
`
`ee
`
`Page 12 of 22
`
`

`

` cal
`
`
`
` 22000
`
`DESCE
`
`
`
`
`*
`
`
`
`
`
`
`
`
`
`
`
`
`
`an adder (202) for providing a sum of said transformed motion compensated signal
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`and the first transformed signal (R1)} to the positive input of the subtractor, and
`
`
`
`-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
` @ Spatial filter W (41) for receiving said sum and for providing a filtered transformed
`
`
`
`
`
`
`
`
`signal (Rf) to the encoding channel.
`
`
`
`‘
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Compared to pre-filtering, the spatialfilter is performed in the encoding part of the
`transcoder.
`
`
`
`
`In such transcoders (200,300,400), the filter is performed on the dequantised data
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`which results in a better accuracy. Best results, so far, were obtained for the combination of
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`spatial filtering of pictures and temporalfiltering of predicted pictures. Successive filtering
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`blocks W can also be merged into a single bicck whose weighting is the product of the
`
`
`
`
`
`
`
`
`
`
`individual weightings without departing from the scope of the invention.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`The drawings and their description hereinbefore refer both to a transcoding device
`
`
`
`
`
`
`
`
`
`
`
`and a method of transcoding, a functional block of a diagram corresponding to a sub-
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`assembly of said device or a step of said method, respectively. They illustrate rather than
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`limit the invention. It will be evident that there are numerous alternatives, which fail within
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`the scope of the appended claims. In this respect, the following closing remarks are made.
`
`
`
`
`
`
`
`
`
`
`
`
`There are numerous ways of implementing functions by means of items of hardware
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`or software, or both. In this respect, the drawings of Fig. 2 to 4 are very diagrammatic, each
`
`
`
`
`
`
`
`
`
`
`
`
`representing only one possible embodiment of the invention. Thus, although a drawing
`
`
`
`
`
`
`
`
`
`
`
`
`
`shows different functions as different blocks, this by no means excludes that a single item of
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`hardware or software carries out several functions. Nor does it exclude that an assembly of
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`items of hardware or software or both carry out a function. For example, thefiltering step
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`can be combined with the quantisation step, thus forming a single step without modifying
`
`
`
`
`
`
`
`
`
`the method of transcoding in accordance with the invention.
`
`
`Said method of transcoding can be implemented in several manners, such as by
`
`
`
`
`
`
`
`
`
`
`
`
`means of wired electronic circuits or, alternatively, by means of a set of instructions stored
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`in a computer-readable medium, said instructions replacing at least a part of said circuits
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`and being executable under the control of a computer or a digital processor in order to carry
`
`out the same functions as fulfilled in said replaced circuits.
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`Any reference sign in the following claims should not be construed aslimiting the
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`claim. It will be obvious that the use of the verb “to comprise” and its conjugations does not
`exclude the presence of any other steps or elements besides those defined in any claim. The
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`word "a” or “an” preceding an element or step does not exclude the presence ofa plurality
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`
`of such elements or steps.
`
`
`
`10
`
`
`
`15
`
`
`20
`
`
`
`25
`
`
`
`30
`
`
`
`35
`
`
`
`
`ck16-07A001
`
`
`
`Page 13 of 22
`
`Page 13 of 22
`
`

`

`
`
`
`THIS PAGE BLANK wsr's
`
`
`
`Page 14 of 22
`
`Page 14 of 22
`
`

`

`2-10-2000
`
`DOOzesoermIOreOOO)
`
`
`
`10
`
`
`
`5
`
`
`
`10
`
`
`15
`
`
`
`1
`
`
`
`A method of transcoding a primary encoded signal (S1) comprising a sequence of
`
`
`
`
`
`
`
`
`
`
`
`
`pictures