WO2008095825A1 - Transcodage vidéo à réduction de la dérive - Google Patents

Transcodage vidéo à réduction de la dérive Download PDF

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Publication number
WO2008095825A1
WO2008095825A1 PCT/EP2008/051005 EP2008051005W WO2008095825A1 WO 2008095825 A1 WO2008095825 A1 WO 2008095825A1 EP 2008051005 W EP2008051005 W EP 2008051005W WO 2008095825 A1 WO2008095825 A1 WO 2008095825A1
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WO
WIPO (PCT)
Prior art keywords
data
transform
residual
requantization
requantization errors
Prior art date
Application number
PCT/EP2008/051005
Other languages
English (en)
Inventor
Philippe Bordes
Anita Orhand
Original Assignee
Thomson Licensing
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Thomson Licensing filed Critical Thomson Licensing
Publication of WO2008095825A1 publication Critical patent/WO2008095825A1/fr

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Classifications

    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/102—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the element, parameter or selection affected or controlled by the adaptive coding
    • H04N19/124—Quantisation
    • H04N19/126—Details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/10—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding
    • H04N19/169—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding
    • H04N19/184—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using adaptive coding characterised by the coding unit, i.e. the structural portion or semantic portion of the video signal being the object or the subject of the adaptive coding the unit being bits, e.g. of the compressed video stream
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/40—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using video transcoding, i.e. partial or full decoding of a coded input stream followed by re-encoding of the decoded output stream
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/48—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using compressed domain processing techniques other than decoding, e.g. modification of transform coefficients, variable length coding [VLC] data or run-length data
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04N—PICTORIAL COMMUNICATION, e.g. TELEVISION
    • H04N19/00—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals
    • H04N19/60—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding
    • H04N19/61—Methods or arrangements for coding, decoding, compressing or decompressing digital video signals using transform coding in combination with predictive coding

Definitions

  • the invention relates to a transcoding device of a first bitstream (S1 ) into a second bitstream (S2), said bitstreams being representative of a same sequence of pictures. More particularly, the invention relates to a transcoding device of the FPDT type (Fast Pixel Domain Transcoder).
  • FPDT Fast Pixel Domain Transcoder
  • a transcoding device is used to modify the coding cost of a sequence of pictures. Indeed, it is sometimes necessary to transfer a bitstream representative of a sequence of pictures of a first network of bandwidth B1 to a second network of bandwidth B2, where B1 > B2.
  • a transcoding device is used to modify the coding cost of said sequence of pictures, i.e. the number of bits used to encode it.
  • Such a transcoding device also enables a bitstream to be adapted to the resources of a terminal or even such a bitstream to be inserted into a multiplex.
  • a transcoding device 1 of the FPDT type according to the prior art is shown in figure 1. It is notably described by G. J. Keesman, in the document entitled “Multi-program Video Data Compression", Thesis Technische Universitat Delft. ISBN 90-74445-20-9, 1995.
  • Such a transcoding device receives at its input a first bitstream S1 representing a sequence of pictures.
  • the input of the transcoding device is connected to an entropy decoding module VLD, itself connected to a first inverse quantization module IQ1.
  • the decoding module VLD decodes part of the first bitstream into current picture data I that are then dequantized by the first dequantization module IQ1 into dequantized data ID with a first quantization step.
  • This first quantization step is itself decoded from the bitstream S1.
  • the picture data I is in the form of coefficient blocks.
  • the quantization module IQ1 is connected to a first input of a first computation module C1.
  • the first computation module C1 is suitable to calculate residual data R.
  • the first computation module C1 carries out the difference between the current dequantized data ID and prediction data PT sent to a second input of the first computation module C1.
  • the output of the first computation module C1 is connected to the input of a quantization module Q2 suitable to quantize the residual data R into quantized residual data RQ with a second quantization step.
  • the second quantization step is determined according to the required bit rate B2.
  • This quantized residual data RQ is then transmitted to an entropy coding module VLC to generate part of the second bitstream. It is also sent to a second dequantization IQ2 operating an inverse quantization from the one operated by the quantization module Q2 and generating dequantized residual data RD. This dequantized residual data RD is then transmitted to a first input of a second computation module C2.
  • the second computation module C2 is suitable to compute requantization errors data E.
  • the second computation module C2 carries out the difference between the dequantized residual data RD and the corresponding residual data R sent to a second input of the second computation module C2.
  • the output of the second computation module C2 is connected to the input of a first IDCT transformation module applying a first transform to the requantization errors data E to generate requantization errors in the spatial domain also called pixel domain, called transform requantization errors data EP.
  • the IDCT module preferentially operates an Inverse Discrete Cosine Transform.
  • the output of the first IDCT transformation module is connected to a memory MEM. Generally, this memory MEM stores over 8-bits each of the data at the output of the first transformation module.
  • the memory is also connected to a prediction module PRED suitable to generate intermediate prediction data P from the transform requantization errors data EP stored in the memory MEM.
  • the prediction module PRED implements, for example, a temporal prediction by motion compensation using motion vectors MVs decoded from the bitstream S1 in the case where the current dequantized data ID is in INTER mode. It can also implement a spatial prediction for example in the case where the current dequantized data is data in INTRA mode as defined in the video coding standard H.264.
  • the intermediate prediction data P is then sent to the input of a second DCT transformation module that applies a second transform to said intermediate prediction data P to generate the prediction data PT.
  • the DCT module preferentially operates a Discrete Cosine Transform. Such a transcoding device 1 has the disadvantage of leading to an effect of temporal or spatial drift.
  • FIG. 2 shows a graph in which curves are shown characterizing the performances obtained with an architecture according to the prior art.
  • the abscissa shows the number of decoded pictures of the sequence and the ordinate the signal to noise ratio or PSNR in decibels of the said decoded pictures with respect to the source pictures.
  • the reference curve 20 corresponds to the decoded pictures of the bitstream S1.
  • the curve referenced 21 corresponds to the decoded pictures of the bitstream S2 at the output of the transcoding device 1 according to the prior art.
  • the drift effect is observed on the curve 21.
  • the quality of the pictures gradually deteriorates until the transcoding of an INTRA type picture.
  • the purpose of the invention is to compensate for at least one disadvantage of the prior art. More particularly, the purpose of the invention is to reduce the drift effect of the device according to the prior art.
  • the invention relates to a transcoding device of a first bitstream into a second bitstream, the two bitstreams being representative of a same sequence of pictures.
  • the device comprises:
  • the device also comprises, to calculate the prediction data: - means for calculating the requantization errors data by subtracting the residual data from the dequantized residual data,
  • the first transformation means are suitable to transform the requantization errors data into transform requantization errors data having a resolution strictly less than 1.
  • the second transformation means are suitable to transform the intermediate prediction data having a resolution strictly less than 1.
  • the memory is suited to store the transform requantization errors data over 8 bits or more than 8 bits
  • figure 1 illustrates a transcoding device according to the prior art
  • figure 2 shows a graph on which are drawn the PSNR curves associated respectively with a sequence of pictures decoded from a bitstream S1 and with the same sequence after transcoding of the bitstream S1 by a device of the prior art
  • figure 3 illustrates a transcoding device according to the invention
  • figure 4 shows a graph on which are drawn the PSNR curves associated respectively with a sequence of pictures decoded from a bitstream S1 , with the same sequence transcoded by a device according to the prior art and with the same sequence transcoded by a device according to the invention.
  • the invention relates to a transcoding device 2.
  • the transcoding device according to the invention is suited to transcode a first bitstream S1 at a first bitrate B1 into a second bitstream S2 at a second bitrate B2, said bitstreams being representative of a sequence of pictures.
  • the digital pictures are tables of image points or pixels coded on 8 bits.
  • Three components are generally coded: one luminance component and two chrominance components. Each component can therefore take 255 different values.
  • the modules of the transcoding device 2 identical to those of the transcoding device 1 are identified in figure 3 using the same references and are not described further.
  • the transcoding device 2 comprises the modules VLD, IQ1 , C1 , Q2, IQ2, C2, PRED and VLC.
  • the transcoding device 2 also comprises a first transformation module IDCT2 as a replacement for the module IDCT1.
  • the first transformation module IDCT2 is suited to apply a first transform on the requantization errors data E in such a manner as to generate transform requantization errors data EP in the spatial domain with a resolution (also called precision) strictly less than 1.
  • the resolution is defined as the smallest interval existing between two data, in this case between two transform requantization errors data generated by the first transformation module IDCT2.
  • the first transform is an inverse discrete cosine transform.
  • a transform that is implemented using adders, subtracters and shift registers gives rise to rounding errors.
  • the last processing operations of the IDCT function described in the MPEG4 AVC standard are right shifts of 6 bits.
  • transform requantization errors data EP is obtained with a resolution equal to 1/4. It is modified so that it generates transform requantization errors data EP
  • the transcoding device 2 also comprises a second transformation module DCT2 as a replacement for the module DCT1.
  • the second transformation module DCT2 is suited to apply a second transform to the prediction data P in such a manner as to generate transform prediction data
  • the second transform is a discrete cosine transform.
  • each of the transform requantization errors data EP is stored in the memory MEM2 over more than 8 bits. According to this embodiment, it is necessary to adapt the prediction module PRED2 so that it can operate on data stored over more than 8 bits, e.g. 10 bits.
  • This embodiment is particularly advantageous to the extent that it can use the prediction module PRED of a transcoding device according to the prior art that is suitable to operate on data stored over 8 bits.
  • This embodiment is particularly advantageous in the case where the transform requantization errors data EP has a limited range values, e.g. [-32 ; +31.75].
  • the transform requantization errors data EP in the slot [-32 ; +31.75] is stored in memory MEM over unsigned 8 bits with a resolution equal to %.
  • Figure 4 shows the same graph as that of figure 2, to which the curve 22 has been added.
  • This curve 22 corresponds to the decoded pictures of the bitstream S2 at the output of the transcoding device 2 according to the invention.
  • the signal to noise ratio is improved in the case where a transcoding device 2 according to the invention is used.
  • the drift effect characteristic of an FPDT type transcoding is reduced.
  • the device according to the invention reduces the rounding errors due to DCT1.

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  • Engineering & Computer Science (AREA)
  • Multimedia (AREA)
  • Signal Processing (AREA)
  • Compression Or Coding Systems Of Tv Signals (AREA)

Abstract

L'invention concerne un dispositif de transcodage. Il comprend : - des moyens de décodage (VLD) d'un premier flux binaire (S1) en données d'image (I), - des moyens de dé-quantification (IQ1) des données d'image (I) en données dé-quantifiées (ID), - des moyens de calcul (C1) de données résiduelles (R), - des moyens de quantification (Q2) des données résiduelles (R) en données résiduelles quantifiées (RQ)1 - des moyens de dé-quantification (IQ2) des données résiduelles quantifiées (RQ) en données résiduelles dé-quantifiées (RD), - des moyens de codage (VLC) des données résiduelles quantifiées (RQ). Il comprend également : - des moyens (C2) de calcul de données d'erreurs de re-quantification (E), - des premiers moyens de transformation (IDCT2) destinés à transformer les données d'erreurs de re-quantification (E) en données d'erreurs de re-quantification transformées (EP) ayant une résolution strictement inférieure à 1, - des moyens de stockage destinés à stocker (MEM2) les données d'erreurs de re-quantification transformées (EP), - des moyens de calcul (PRED2) de données de prédiction intermédiaires (P) à partir des données d'erreurs de re-quantification transformées stockées (EP), - des seconds moyens de transformation (DCT2) destinés à transformer les données de prédiction intermédiaires (P) en données de prédiction (PT).
PCT/EP2008/051005 2007-02-05 2008-01-29 Transcodage vidéo à réduction de la dérive WO2008095825A1 (fr)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
FR0753053 2007-02-05
FR0753053 2007-02-05

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Cited By (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103546755A (zh) * 2013-08-22 2014-01-29 合一网络技术(北京)有限公司 固定码率的自适应分辨率转码方法

Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998027735A1 (fr) * 1996-12-17 1998-06-25 Thomson Consumer Electronics, Inc. Appareil de compression de memoire efficace et quantificateur pour un systeme de traitement d'images
WO2002098136A2 (fr) * 2001-05-29 2002-12-05 Koninklijke Philips Electronics N.V. Procede et dispositif de transcodage video

Patent Citations (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO1998027735A1 (fr) * 1996-12-17 1998-06-25 Thomson Consumer Electronics, Inc. Appareil de compression de memoire efficace et quantificateur pour un systeme de traitement d'images
WO2002098136A2 (fr) * 2001-05-29 2002-12-05 Koninklijke Philips Electronics N.V. Procede et dispositif de transcodage video

Non-Patent Citations (1)

* Cited by examiner, † Cited by third party
Title
KEESMAN G ET AL: "Transcoding of MPEG bitstreams", SIGNAL PROCESSING. IMAGE COMMUNICATION, ELSEVIER SCIENCE PUBLISHERS, AMSTERDAM, NL, vol. 8, no. 6, September 1996 (1996-09-01), pages 481 - 500, XP004047113, ISSN: 0923-5965 *

Cited By (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
CN103546755A (zh) * 2013-08-22 2014-01-29 合一网络技术(北京)有限公司 固定码率的自适应分辨率转码方法
CN103546755B (zh) * 2013-08-22 2015-05-20 合一网络技术(北京)有限公司 固定码率的自适应分辨率转码方法

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