US 2006/0133479 A1Published application

Method and apparatus for generating a quantisation matrix that can be used for encoding an image or a picture sequence

OwnerYing Chen, Jiefu Zhaiinventors

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Abstract

A significant data rate reduction effect in video coding is acchieved by quantizing the transformed frequency coefficients or components of a pixel block so that thereafter fewer amplitude levels need to be encoded and part of the quantised amplitude values becomes zero and need not be encoded as quantised amplitude values. Many transform based video coding standards use a default quantization matrix to achieve better subjective video coding/de-coding quality. A quantization matrix assigns smaller scaling values to some frequency components of the block if the related horizontal and/or vertical frequencies are believed to be the less important frequency components with respect to the resulting subjective picture quality. The inventive quantization matrix generation starts from default quantization matrices and derives therefrom a perceptually optimum quantization matrix for a given picture sequence. In a first pass the candidate quantization matrix for a given picture sequence is iteratively constructed by simultaneously increasing scaling values for some coefficient positions and decreasing scaling values for other ones of the coefficient positions. In a second pass the generated quantization matrix is applied for re-encoding the picture sequence.

Claims19

Dependent claims

Method for generating) a quantization matrix that can be used for encoding an image or a picture sequence, in which encoding blocks of transformed coefficients related to pixel difference blocks or predicted pixel blocks are quantised or additionally inversely quantised using said quantization matrix, in which matrix a specific divisor is assigned to each one of the coefficients positions in a coefficient block, said method comprising the steps:

loading a pre-determined quantization matrix that includes one divisor for a transformed DC coefficient and multiple divisors for transformed AC coefficients as a candidate quantization matrix;
for a given picture or picture sequence, or for a slice in a given picture or picture sequence, iteratively:
a) increasing in said candidate quantization matrix one or more of said AC coefficient divisors, while decreasing in said candidate quantization matrix one or more other ones of said AC coefficient divisors,
b) measuring for the changed divisors of the resulting updated candidate quantization matrix whether or not—when applying the updated candidate quantization matrix in said encoding—the resulting picture encoding/decoding quality is improved, and if true, allowing for the following iteration loop further increase or decrease, respectively, of said changed divisors, and if not true, trying other ones of said divisors for an increase and for a decrease and/or reversing the increase and decrease for said changed divisors;
c) checking for each one of said changed divisors whether or not it has been increased as well as decreased in the iteration loops and if true, assigning a predetermined marking value to such divisor, and calculating from said divisor marking values a matrix status value;
if the number of iterations exceeds a first threshold value or the matrix status value exceeds a second threshold value, outputting the latest candidate quantization matrix as said quantization matrix.

3 more elements

Apparatus for generating a quantization matrix that can be used for encoding an image or a picture sequence, in which encoding blocks of transformed coefficients related to pixel difference blocks or predicted pixel blocks are quantised or additionally inversely quantised using said quantization matrix, in which matrix a specific divisor is assigned to each one of the coefficients positions in a coefficient block, said apparatus comprizing means being adapted for:

loading a pre-determined quantization matrix that includes one divisor for a transformed DC coefficient and multiple divisors for transformed AC coefficients as a candidate quantization matrix;
for a given picture or picture sequence, or for a slice in a given picture or picture sequence, iteratively:
a) increasing in said candidate quantization matrix one or more of said AC coefficient divisors, while decreasing in said candidate quantization matrix one or more other ones of said AC coefficient divisors,
b) measuring for the changed divisors of the resulting updated candidate quantization matrix whether or not—when applying the updated candidate quantization matrix in said encoding—the resulting picture encoding/decoding quality is improved, and if true, allowing for the following iteration loop further increase or decrease, respectively, of said changed divisors, and if not true, trying other ones of said divisors for an increase and for a decrease and/or reversing the increase and decrease for said changed divisors;
c) checking for each one of said changed divisors whether or not it has been increased as well as decreased in the iteration loops and if true, assigning a predetermined marking value to such divisor, and calculating from said divisor marking values a matrix status value;
if the number of iterations exceeds a first threshold value or the matrix status value exceeds a second threshold value, outputting the latest candidate quantization matrix as said quantization matrix.

3 more elements

Dependencies are inferred from the claim text.

Facts

Application: 11/293,610Filed 2 Dec 2005
Priority: EP 04300939.822 Dec 2004
Published: 22 Jun 2006
Term ends: Not estimatedThe source records don’t support an estimate.

Classification10 codes

H04N 19/192
Characterised by the adaptation method, adaptation tool or adaptation type used for the adaptive coding: the adaptation method, adaptation tool or…
H04N 19/126
Quantisation: details of normalisation or weighting functions, e.g. normalisation matrices or variable uniform quantisers
H04N 19/134
Using adaptive coding: characterised by the element, parameter or criterion affecting or controlling the adaptive coding
H04N 19/154
Characterised by the element, parameter or criterion affecting or controlling the adaptive coding: measured or subjectively estimated visual…