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`GOOGLE EXHIBIT 1016
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`Office européen
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`Les documentsfixés a Yer
`Die angehefteten Unteria-
`The attached documents
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`ursprdnglich eingereichten European patent application conformes a !a version
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`Fassung der auf dem nach- described on the following_initialernent déposée de CO
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`la demande de brevet
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`europaischen Patentanmel-
`européen spécifiée ala
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`dung dberein.
`page suivante.
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`Europdlsches
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`9 Patentamt
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`European
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`Patent Office
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`Bescheinigung
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`Certificate
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`des brevets
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`Attestation
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`Patent application No. Demande de brevet n°
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`01400588. 8
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`Der Prasident des Eurapdischen Patentarmts;
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`Im Auftrag
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`For the President of the European Patent Office
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`Le Président de |’Office eurepéen des brevets
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`p.o.
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`1.L.C. HATTEN-HECKMAN
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`DEN HAAG, DEN
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`THE HAGUE,
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`LA HAYE,LE
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`11/10/01
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`EPA/SEPO/OQEB Form
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`Office européen
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`des brevets
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`Anmeldetag:
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`Date of filing
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`Date de dépét:
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`06/03/01
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`01400588.8
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`Anmeldung Nr.:
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`Application no.:
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`Demande n*:
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`Anmelder.
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`Applicant(s):
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`Demandeur(s}
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`Koninklijke Philips Electronics N.¥.
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`5621 BA Efndhoven
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`NETHERLANDS
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`Bezaichnung der Erfindung:
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`Title of the invention:
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`Titre de Vinvention:
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`Method of transmitting and transcoding device with embedded filters
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`In Anspruch genommene Prionat(en} / Priority(ies) claimed / Priorité{s) revendiquée(s}
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`Staat:
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`internationale Patentkiassifikation:
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`Am Anmeidetag benannte Vertragstaaten:
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`Contracting states designated at date of filing: AT/BE/CH/CY/DE/DK/ES/FI/FR/G B/G RVIEAIT/LIAZLU/MC/NL/PTAS EVTR
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`IRRomen ene, ssEEREENmeemeetpemren
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`Pyinieck? 1-10-2001
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`Method of transcoding and transcoding device with embedded filters
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`FIELD OF THE INVENTION
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`The present invention relates to a method of transcoding a primary encoded signal
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`comprising a sequence of pictures, into a secondary encoded signal, said method of
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`transcoding comprising at least the stepsof:
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`decoding a current picture of the primary encoded signal, said decoding step
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`comprising a dequantizing sub-step for providing a first transformed signal,
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`encoding, following the decoding step, for obtaining the secondary encoded signal,
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`sald encoding step comprising a quantizing sub-step.
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`The invention also relates to a corresponding device for carrying out such a method
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`This invention is particularly. relevant for the transcoding of MPEG encoded video
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`BACKGROUNDOF THE INVENTION
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`Bit-rate transcoding is a technique which allows a primary video stream encoded at
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`a bit-rate BR1 to be converted into a secondary video stream encoded at a bit-rate BR2
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`imposed by the means of transport during broadcasting. A transcoding device as described
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`in the opening paragraph is disclosed in the European Patent Application n° EP 0690 392
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`(PHF 94001) and is depicted in Fig. 1. Said device (100) for transcoding encoded digital
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`signals (S1) which are representative of a sequence of images, comprises a decoding
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`channel (11,12) followed by an encoding channel (13,14,15). A prediction channel is
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`in series, between two subtractors (101,102), an inverse discrete cosine transform circuit
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`IDCT (16), a picture memory MEM (17), a circuit for motion compensation MC (18) in view
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`of displacement vectors (V) which are representative of the motion of each image, and a
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`SUMMARYOF THE INVENTION
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`It is an object of the invention to provide a method of transcoding and a
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`corresponding device that allows a better quality of pictures for low bit-rate applications. The
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`present invention takes the following aspect into consideration.
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`OOnOSeOn
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`Printeck1 1-10-2001
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`With the advent of home digital video recording of MPEG broadcasts, transcoders
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`can be used in consumer devices to implement long play modes or to quarantee the
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`recording time. However, the input signal to be transcoded has often been encoded at a
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`variable bit-rate with a low averagebit-rate. This is due to the generalization of statisticai
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`multiplexing that allows broadcasters to put a lot of video programs in a multiplex in order to
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`method of transcoding according to the prior art, will lead to conspicuous quantization
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`applications.
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`To overcome this drawback, the method of transcoding in accordance with the
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`invention is-characterized in that it further comprises a filtering step betweén the
`dequantizing sub-step and the quantizing sub-step.
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`The transcoding method in accordance with the invention allows to implementfilters
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`in the transcoder of the prior art at a negligible cost. Those filters can be tuned to control
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`the static and dynamic resolution and also to perform noise reduction. For the same number
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`of bits, the filtered transformed signal is encoded with a smaller quantization scale thus
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`reducing visual artifacts such as biocking, ringing and mosquito noise.
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`In a first embodiment of the invention, the method of transcoding comprises a step
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`of predicting a transformed motion compensated signal from a transformed encoding error
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`derived from the encoding step, said prediction step being located between the encoding
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`and decoding steps, and is characterized in that the filtering step is a temporalfiltering step
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`for receiving the transformed motion compensated signal and thefirst transformed signal
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`and for providing a filtered transformed signal to the quantizing sub-step.
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`Such a temporalfiltering step allows to perfarm noise reduction using, for example,
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`@ recursive filter. As a consequence, bits are only spent on the useful information contained
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`in the picture and the picture quality is thus increased.
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`In a second embodiment of the invention, the method of transcoding also comprises
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`@ prediction step and is characterized in that the filtering step is a spatial filtering step for
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`receiving the first transformed signal and for providing a filtered transformed signal, said
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`filtered transformed signal and the transformed motion compensated signal being provided
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`Such a spatial filtering allows a reduction of the sharpness of the picture and
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`decreases the possible source of ringing and mosquito noise.
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`The present invention also relates to a corresponding device for carrying out such a
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`method of transcoding.
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`06-08-2001
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`The presentinvention finally relates to a computer program product for a receiver,
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`such as a digital video recorder or a set-top-box, that comprises a set of instructions, which,
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`when loaded into the receiver causes the receiver to carry out the method of transcoding.
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`These and other aspects of the invention will be apparent from and will be
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`elucidated with reference to the embodiments described hereinafter.
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`BRIEF DESCRIPTION OF THE DRAWINGS
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`The present invention will now be described in more detail, by way of example, with
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`reference to the accompanying drawings, wherein :
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`Fig. 1 is a block diagram correspondingto a transcoding device according to the prior
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`Fig. 2 is a block diagram corresponding to a first embodiment of a transceding device
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`according to the invention, said device comprising a temporalfilter circuit,
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`Fig. 3 is a block diagram corresponding to a second embodiment of a transcoding device
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`according to the invention, said device comprising a spatialfilter circuit,
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`Fig. 4 a block diagram corresponding to a third embodiment of a transcoding device
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`according to the invention, said device also comprising a spatialfilter circuit, and
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`Fig. 5 a block diagram corresponding to a fourth embodiment of a transcoding device
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`according to the invention, said device also comprising a spatialfilter circuit and,
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`possibly, a temporalfilter circuit.
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`DETAILED DESCRIPTION OF THE INVENTION
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`The present invention relates to an improved method of and a corresponding device
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`for transceding video encoded signals. It relates, more especially, to MPEG-2 encoded
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`signais but it will be apparent to a person skilled In the art that said method of transcoding
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`stays also applicable to any type of video signals encoded using a block-based technique
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`such as, for exampie, those provided by MPEG-1, MPEG-4, H-261 or H-263 standards.
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`A transcoding device allows a primary encoded signal (Si) previously encoded with a
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`first quantization scale and comprising a sequence ofpictures, to be converted into a
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`secondary encoded signal ($2) encoded with a second quantization scale.
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`Such a transcoding device comprises at least the following elements:
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`decoding a current picture of the primary encoded signal and for providing a first
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`an encoding unit comprising a quantizer Q, a variable length encoder VLC for obtaining
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`_—
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`Breetoro
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`OEoosee
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`a prediction unit, between the encoding unit and the decoding unit, and comprising in
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`series :
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`an inverse discrete transform circuit IDCT (an Inverse Discrete Cosine Transform in
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`the case of MPEG),
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`a picture memory MEM,
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`a circuit MC for motion compensation in view of displacement vectors which are
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`a discrete transform circuit DCT for predicting a transformed motion compensated
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`signal (Rmc) from a transformed encoding error (Re) derived from the encoding
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`unit,
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`an adder for determining a sum of the transformed motion compensated signa! and
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`a transformed signal (R1 or Rf),
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`a Subtractor for determining the transformed encoding error from a difference
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`unit,
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`a filter circuit, between the first dequantizer and the quantizer, for providing a filtered
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`Said filter circuit can be a temporal or a spatial filter circuit adapted to control the
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`static and dynamic resolution and to perform noise reduction on a picture. The different
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`implementations of such filters are described in the following Figs. 2 to 5.
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`It will be apparent to a person skilled in the art that the result of the transcoding
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`device is unchanged if the adderis replaced by another subtractor adapted to determine a
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`difference between a transformed signal (R1 or Rf) and the transformed motion
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`compensated signal (Rmc) andif the first cited subtractor is adapted to determine the
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`transformed encoding error (Re) from a difference between the second transformed signal
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`(R2) and the output of the other subtractor.
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`In a first embodiment of the invention, the transcoder implements a motion
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`compensated temporalfilter. Temporal filtering allows to reduce signals which are not
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`correlated from frame to frame. It can very effectively reduce noise when combined with
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`motion compensation, as motion compensation tries to correlate the image content from
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`frame to frame. In this embodiment, a recursive filter is implemented since it provides a
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`better selectivity at lower cost.
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`A nalve transcoding chain with a motion compensated recursive temporalfilter
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`usually comprises in cascade :
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`a decoder for providing motion compensated blocks Di of decoded pictures from an
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`i
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`03-08-2001
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`re MEN os Shee
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`Crees
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`OS
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`o1aooses
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`5
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`-
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`(1)
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`a recursive temporalfilter for providing filtered blocks Df of decoded pictures, and
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`an encoder for providing an output stream and motion compensated blocks D2 of locally
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`decoded pictures after encoding.
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`To reduce costs, the motion compensation In the encoder is re-used in the recursive
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`temporal filter. Thus, the signal D2 is fed back to said filter instead of Df. The filtering
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`equation of a motion compensated block Df{n,m) is then :
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`Df(h,m)= (1 - a)- Di(n, m)+ « -MC(D2(p(n)), Vin, mn},
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`where :
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`n is the index of the current picture,
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`- mis the index of a block of said current picture,
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` V(n,m) is the motion associated with block m, of picture n,
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`p(n) Is the index of the anchor picture associated with image n,
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`MC is the motion compensation operator, and
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`ais a positive scalar smaller than one that tunes the filter response.
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`An expression similar to equation (1) can be drawn for bidirectional motion
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`compensation. However, without loss of generality, we shall restrict the demonstration to
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`the unidirectional case. Note that intra encoded blocks cannot be filtered since no prediction
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`is formed for them. Yet, intra encoded blocks in non intra pictures correspond most often to
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`newly exposed regions that could not possibly be temporally filtered.
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`The naive transcoding chain can be simplified using the hypothesis that the motion
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`compensation information is unchanged. To this end, the motion compensated block
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`Di(n,m) is expressed as follows :
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`Di(n,m) = Mt -R1(n,m)-M+MC(D1(p(n)), vin,m)),
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`where ;
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`- Mis the 8 x 8 discrete cosine transform matrix,
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` M*is the corresponding transposed matrix, and
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`R1(n,m) is the residue retrieved from the input bit-stream after variable length
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`decoding VLC and dequantization IQ.
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`M is defined by equation (3) and is such that MM' =1:
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`ifi= 0,
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` |cos(in (2)+1)/16)/2 otherwise.
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`Then, the filtered block is encoded using the same motion compensation
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`information. Let Rf(n,m) be the corresponding residue :
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`Rf(n,m) = M-Df(n,m)- mt - M-MC(D2(p(n)), V(n, m)}-M*.
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`The residue is then quantized and dequantized again to compute the locally decoded
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`pictures D2. Let R2(n,m) be the quantized and dequantized residue:
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`My,
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`=
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`(3)
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`Printedk1 1-10-2001
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`D2:
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`DESCMEE
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`6
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`OMMOOsee
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`R2(n,m) = M-D2(n,m)-Mé -M-MC(D2(p(n)), V(n,m))- Mt
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`The equations (1) and (4) are combined so that Rf is derived directly from D1 and
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`(5)
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`RF(n,m) = (t—a)[M-D1{n,m)-Mt —M-MC(O2(p(n)), vin, m)-M
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`Combining the equation (2) with equation (6) gives :
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`Rf(n,m)= (1 -«)[ Ri(fn,m)+M-MC{O1(p(n)), Vin, m))- Mt
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`—M-MC{02(p(n)),Vn,m))-M*].
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`Since motion compensation is performed identically from D1 and from D2, the
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`motion compensation operator MC can operate on the picture difference,i.e., on the error
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`signal due to the transcoding operation. Defining 8D = D1 - D2, equation (7) is rewritten as
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`follows :
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`Re(n,m)=(1-2) [R1(n,m)+M-MC(sD(p(n)), Via, m))-M* (8)
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`The error signal 5D can be derived from the prediction errors, combining equations
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`(5) and (6):
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`(6)
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`7)
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`Equations (8) and (9) define the transcoder structure depicted in Fig. 2. Said
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`transcoder (200) comprises :
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`a decoding channel comprising a variable length decoder VLD (11) anda first
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`dequantizer IQ (12) for decoding a current picture of a primary enceded signal (S1) and
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`for providing a first transformed signal (R1),
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`an encoding channel comprising a quantizer Q (13), a variable length encoder VLC (14)
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`for obtaining the secondary encoded siqnal (S2), and a second dequantizer IQ (15) for
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`providing a second transformedsignal (R2),
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`a prediction channel comprising, in series :
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`a subtractor (201) for determining a transformed encoding error (Re) and whose
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`negative input receives the second transformed signal,
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`an inverse discrete cosine transform circuit IDCT (16),
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`a picture memory MEM (17),
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`acircuit for motion compensation MC (18),
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`‘
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`30 #.adiscrete cosine transform circuit DCT (19) for predicting a transformed motion
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`compensated signal (Rmc)},
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`an adder (202) for providing a sum of the transformed motion compensated signal
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`and the first transformed signal (R1) to the positive input of the subtractor,
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`(9)
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`{
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`SD(n,m)= Mt[en)_Raf,m) -M.
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`ae
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`Feritedaipeos200;) a
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`DES
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`a temporalfilter circuit Wt (21) for receiving said sum and for providing the filtered
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`transformed signal (Rf) to the quantizer Q (13).
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`In an advantageous embodiment of the invention, the strength of the motion
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`compensated recursive temporalfilter is adjusted separately for each transformed coefficient
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`Rf[i], i.e., for each DCT sub-band. The transformed coefficient of rank i is multiplied by W{]i]
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`= 1- afi] suchas:
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`RELI] = WE} (Rifi] + Rmc[ij)
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`Thus, the noise reduction can be tuned to the spectral shape of the noise. It can also be
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`decided notto filter low frequencies in order to avoid visible artifact in case of a bad motion
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`compensation and in order to reduce the noise.
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`(10)
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`In the second and third embodiments of the invention, the transcoder implements a
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`spatialfilter. Spatiaifiltering is not so efficient to reduce the noise as motion compensated
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`temporalfiltering is. Yet, it can prevent block artifacts at low bit-rate, smoothing down sharp
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`edges that would otherwise create ringing effects. It can also simplify complex patterns that
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`would be otherwise randomly distorted from one picture to the other, resulting in the so-
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`Let us consider again the naive transcoding chain. The pixel domainfilter shall have
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`a granularity which is the same as the granularity of the decoder. Thus we consider a block-
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`wise filter, Let Di(n,m) be block m of picture n. The filtered block Di(n,m) is computed as
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`foliows :
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`Df(n,m) = Fv{n)- Difn,m)-Fh'(n)
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`where Fv(n) and Fh(n) are matrices that define respectively the verticai and
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`horizontal filtering within the block.
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`Combining the equation (11) with the equation (2), we find :
`Df(n,m) = Fv(n)-M* -Ri(n,m)-M-Fh*(n)
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`(12)
`+ Fv(n)- MC(D1(p(n)), V(n, m))- Frt(n)
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`Tf the filter is the same for a group of pictures, then Fv(n) = Fv(p(n)) and Fh(n) =
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`Fh(p(n)). Thus, the following approximation can be given for equation (12} based on the
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`assumption that block-wise filtering commutes with motion compensation :
`Df(n,m) = Fv(n)-Mé -Ri(p,m)-M-Fht (a) +MC{OF(p(n)), vin, m))
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`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 spatial filter in the transcoder, the
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`residue Ri(n,m) needs to be substituted by :
`Rf(n,m) = M-Fv(n)-M® -R1(n,m)-M-Fh*(n)- Me
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`BocaoeeOon
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`=. re,
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`Ozooses)
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`Evenif the matrices M-Fv{n)-M' and M-Fh'(n).M! can be pre-computed, their
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`computing seems to involve many operations. Said computing can be simplified for a class of
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`block-wise filters for which the two matrices are diagonal. Such filters are symmetric filters
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`with an even numberof taps. In our embodiment, we consider normalized 3-tap symmetric
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`filters since they are more suitable for small blocks. Such filters have a single parameter,
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`denoted a. The corresponding pixel domain filtering matrix, (F,poaj<a, is defined by :
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`a
`fori=j=1ito6,
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`fi
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`1
`F, =——i 24a|i+a fori=j=Oand7,
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`otherwise.
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`(15)
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`Then,
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`M.-F,
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`-Mb = ———2+a {o
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`1
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`(2cos(in/8)+a
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`otherwise.
`fori=j
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`(16)
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`Thus, to implementfiltering with horizontal parameter a, and vertical parametera,,
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`the residue R1(n,m) needs to be weighted (component-wise) by (Ws,jJoas<a defined as
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`follows :
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`Ws, =2eeslal)+2. 2eoeln/s)+2,
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`an)
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`Fig. 3 shows a transcoder with spatial pre-filtering according to the second
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`embodiment of the invention. Said transceder (300) comprises :
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`a decoding channel comprising a variable length decoder VLD (11) and a first
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`dequantizer IQ (12) for providing a first transformed signal (R1),
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`a Spatialfilter circuit Ws (31) for receiving said first transformed signal and for providing
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`the filtered transformed signal (Rf),
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`an encoding channel comprising a quantizer Q (13), a variable length encoder VLC (14)
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`and a second dequantizer IQ (15) for providing a second transformed signal (R2),
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`a prediction channel comprising, in series :
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`a subtractor (201) for determining a transformed encoding error (Re) and whose
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`negative input receives the second transformed signal,
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`an inverse discrete cosine transform circuit IDCT (16),
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`a picture memory MEM (17),
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`a ireuit for motion compensation MC (18),
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`a discrete cosine transform circuit DCT (19) for predicting a transformed motion
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`compensated signal (Rmc), and
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`anadder (302) for providing a sum of said transformed motion compensated signal
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`and thefiltered transformed signal (Rf) to the positive input of the subtractor.
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`03-08-2001 E
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`MOTE Toten.
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`Fig. 4 is a transcoder according to the third embodiment of the invention, with
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`spatial post-filtering whose weighting factors are Ws,;. Said transcoder (400) comprises :
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`a decoding channel comprising a variable length decoder VLD (11) andafirst
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`dequantizer 1Q (12) for providing a first transformed signal (R1),
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`an encoding channel comprising a quantizer Q (13), a variabie length encoder VLC (14)
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`and a second dequantizer 1Q (15) and further comprising an inversefilter circuit (42) for
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`providing a second transformed signal (R2),
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`& prediction channel comprising, in series :
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`a subtractor (201) for determining a transformed encoding error (Re} and whose
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`negative input receives the second transformed signal,
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`an inverse discrete cosine transform circuit IDCT (16),
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`a circuit for motion compensation MC (18),
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`a discrete cosine transform circuit DCT (19) for predicting a transformed motion
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`anadder (202) for providing a sum of said transformed motion compensated signal
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`and the first transformed signal (R1} to the positive input of the subtractor, and
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`@ spatial filter circuit Ws (41) for teceiving said sum and for providing a filtered
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`transformed signal (Rf) to the encoding channel.
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`Compared to pre-filtering, the spatial filtering is performed in the encoding part of
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`Fig. 5 is a transcoder according to the fourth embodiment of the invention, with
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`spatial post-filtering. Said transcoder (500) comprises:
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`a decoding channel comprising a variable length decoder VLD (11) and a first
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`dequantizer IQ (12) for providing a first transformed signal (R1),
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`an encoding channel comprising a quantizer Q (13), a variable length encoder VLC (14)
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`a prediction channel comprising, in series a subtractor (201) for determining a
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`transformed encoding error (Re) and whose negative input receives the second
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`transformed signal, an inverse discrete cosine transform circuit IDCT (16), a picture
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`memory MEM (17), a circuit for motion compensation MC (18), a discrete cosine
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`transform circuit DCT (19) for predicting a transformed motion compensated signal
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`(Rme}, and an adder (202) for providing a sum of said transformed motion compensated
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`signal and the first transformed signal (R1) to the positive input of the subtractor.
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`Said transcoder further comprises a switch (52) having at least two positions. In a
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`first position (a) of the switch, a spatial filter circuit Ws (51) is adapted to receive the output
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`Page 14 of 27
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`Page 14 of 27
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`§ Printedk1 1-10-2001
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`DESS
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`OOseS
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`ap3a- -
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`BN ee
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`ae wee
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`of the adder and to provide a filtered transformed signal (Rf) to the quantizing circuit (13).
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`In that case, and contrary to Figs. 3 and 4, the spatialfilter circuit is not applied to every
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`macroblocks contained in the current picture but is only applied to intra coded macroblocks
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`contained in said picture. In a second position (b) of the switch, no filtering is applied : this
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`position corresponds mainly to n