Video data encoder and decoder

• US 6,272,178 B1
• Filed: 10/15/1998
• Issued: 08/07/2001
• Est. Priority Date: 04/18/1996
• Status: Expired due to Term

• Current Assignee: Nokia Solutions and Networks US LLC (Nokia Corporation)
• Original Assignee: Nokia Mobile Phones UK Limited (Nokia Corporation)
• Inventors: Kalevo, Ossi, Nieweglowski, Jacek, Tûrker, Mustafa Ali, Haavisto, Petri
• Primary Examiner(s): Kelley, Chris
• Assistant Examiner(s): An, Shawn S.
• Application Number:
  US09/171,262
• Time in Patent Office: 1,027 Days
• Field of Search: 348/699, 375/240, 375/405, 375/407, 375/406
• US Class Current: 375/240.03
• CPC Class Codes: H04N 19/12 Selection from among a plurality of transforms or standards, e.g. selection between discrete cosine transform [DCT] and sub-band transform or selection between H.263 and H.264
• CPC Class Codes: H04N 19/132 Sampling, masking or truncation of coding units, e.g. adaptive resampling, frame skipping, frame interpolation or high-frequency transform coefficient masking
• CPC Class Codes: H04N 19/14 Coding unit complexity, e.g. amount of activity or edge presence estimation H04N19/146 takes precedence
• CPC Class Codes: H04N 19/146 Data rate or code amount at the encoder output
• CPC Class Codes: H04N 19/149 by estimating the code amount by means of a model, e.g. mathematical model or statistical model
• CPC Class Codes: H04N 19/15 by monitoring actual compressed data size at the memory before deciding storage at the transmission buffer
• CPC Class Codes: H04N 19/17 the unit being an image region, e.g. an object
• CPC Class Codes: H04N 19/176 the region being a block, e.g. a macroblock
• CPC Class Codes: H04N 19/44 Decoders specially adapted therefor, e.g. video decoders which are asymmetric with respect to the encoder
• CPC Class Codes: H04N 19/61 in combination with predictive coding
• CPC Class Codes: H04N 19/94 Vector quantisation
• CPC Class Codes: H04N 19/97 Matching pursuit coding

Abstract

This invention relates to compression of prediction error in motion compensated video coding schemes. Prediction frame and motion vectors are used to extract useful information about the properties of the prediction error signal, e.g. its location, directionality, etc. This information does not need to be transmitted because the decoder of the proposed system includes means to extract this information. Information extracted by the encoder and decoder is used to adapt prediction error coding scheme which gives substantial bitrate reductions.

Claims

1. Encoder for performing motion compensated encoding of video data, comprising:

means (8) for estimating motion vectors describing scene motion displacements of video frame pixels;

means (7) for predicting a video data frame (P) based on a first video data frame (R) and said motion vectors;

means (1) for calculating a prediction error frame (E) based on said predicted video data frame (P) and on a second video data frame (I);

means (2) for encoding said prediction error frame (E) and obtaining prediction error data;

means (4) for transmitting said motion vectors and said prediction error data to a decoder;

said means (2) for encoding said prediction error frame (E) comprising;

means (24) for partitioning said prediction error frame into a plurality of areas; and

determination means for performing at least one of the following operations;

determination of areas in said prediction error frame (E) to be encoded and determination of at least one coding scheme for each area to be encoded of said prediction error frame (E); and

area encoding means (26) for encoding the areas to be encoded of said prediction error frame (E) in accordance with the at least one determination operation of said determination means;

wherein said determination means is adapted to analyse properties of said predicted video data frame (P) and to perform said at least one determination operation based on said analysis.

2. Encoder according to claim 1, characterized in that

said determination means comprises means (22) for analysing for each area of said prediction error frame a discontinuity of the image brightness in a corresponding area of the predicted video data frame (P); and

said determination means (2) is adapted to perform said at least one operation based on said discontinuity analysis.

3. Encoder according to claim 2, characterized in that said discontinuity analysing means (22) comprises:

a linear filter for calculating finite differences (F_H) in a vertical direction and a linear filter for calculating finite differences (F_V) in a horizontal direction in each area of the predicted video data frame (P); and

means for comparing the sum of absolute values of the outputs of both filters in each area with a first predetermined threshold;

said determination means being adapted to determine that an area of the prediction error frame (E) is not to be encoded if said sum of absolute values calculated for the corresponding area of said predicted video data frame (P) does not exceed said first threshold.

4. Encoder according to claim 1, characterized in that:

said area encoding means (26) comprises selection means (28, 29) for individually selecting an area encoder (27₁, . . . , 27_n) for each area determined to be encoded among a plurality of different area encoders.

5. Encoder according to claim 4, characterized in that:

said determination means comprises classifying means (23) for assigning one class of a group of property classes to each area to be encoded of said prediction error frame (E) depending on brightness discontinuity properties of the corresponding area of said predicted video data frame (P); and

said selection means (28, 29) is adapted to select an area encoder (27₁, . . . , 27_n) for each area to be encoded in accordance with the class assigned to the respective area.

6. Encoder according to claim 5, characterized in that:

said classifying means (23) is adapted to perform a classification based on output values provided by linear directional filters (22) for calculating finite differences (F_H) in a vertical direction and finite difference (F_V) in a horizontal direction in each area of the predicted video data frame (P) that corresponds to an area to be encoded of said prediction error frame (E).

7. Encoder according to claim 5, characterized in that

said classifying means (23) is adapted to perform a classification based on respective brightness discontinuity concentrations in different pixel clusters of each area of the predicted video data frame (P) that corresponds to an area to be encoded of said prediction error frame (E).

8. Encoder according to claim 6, characterized in that:

said group of classes includes at least one of the following classes;

no discontinuities;

horizontal discontinuities;

vertical discontinuities;

diagonal left slanted discontinuities;

diagonal right slanted discontinuities;

non-directional discontinuities.

9. Encoder according to claim 1, characterized in that:

said area encoding means (26) is adapted to encode the data of each area to be encoded of said prediction error frame (E) by means of using selected orthogonal transformations or vector quantization or matching pursuit schemes.

10. Encoder according to claim 4, characterized by

each area encoder (271, . . . , 27n) being adapted to comprise a plurality of coding methods (531 to 53k);

coding method selection means (51, 54, 55) provided for each area encoder (271, . . . , 27n) for selecting a coding method from the respective plurality of coding methods (531 to 53k) in accordance with a criterion related to the performance of the coding methods; and

means (52, 56) for communicating the selection by said coding method selection means (51,54,55) to a video decoder.

11. Encoder according to claim 10, characterized in that said pluralities of coding methods (531, . . . , 53n) are different for different area encoders (271, . . . , 27n).

12. Encoder according to claim 1, characterized by:

a prediction error decoder (3) for decoding said prediction error frame (E); and

means (5) for calculating said first video data frame (R) based on said predicted video data frame (P) and said decoded prediction error frame (E*).

13. Encoder according to claim 1, characterized in that:

said determination means (25) comprises means for calculating for each area of said predicted video data frame (P) a magnitude and/or direction of corresponding motion vectors; and

said determination means (22, 25) is adapted to perform said determination based on the calculated magnitude and/or direction of said motion vectors.

14. Encoder according to claim 13, characterized in that:

said determination means is adapted to determine that an area of the prediction error frame (E) is not to be encoded if said calculated magnitude of said motion vectors corresponding to the area does not exceed a second predetermined threshold.

15. Method of motion compensated encoding of video data, comprising the steps:

estimating motion vectors describing scene motion displacements of video frame pixels;

predicting a video data frame (P) based on a first video data frame (R) and said motion vectors;

calculating a prediction error frame (E) based on said predicted video data frame (P) and a second video data frame input;

encoding said prediction error frame (E) and obtaining prediction error data;

transmitting said motion vectors and said prediction error data to a decoder;

said step of encoding said prediction error frame (E) comprising;

dividing said prediction error (E) frame into a plurality of areas;

performing at least one of the following determination operations;

determining which of the areas in said prediction error frame (E) are to be encoded and determining a coding scheme for each area to be encoded of said prediction error frame (E); and

encoding each area to be encoded of said prediction error frame (E) in accordance with said determination;

wherein said at least one determination operation is based on analysing properties of said predicted video data frame (P).