Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-05-22
2004-09-21
Vo, Tung (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06795498
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an decoding apparatus, a decoding method, an encoding apparatus, an encoding method, an image processing system and an image processing method, all fit for use in a system that encodes image data again. In particular, the invention relates a decoding apparatus and method for decoding a bit stream to generate image data and encoding parameters for use in encoding the image data again, to an encoding apparatus and method for encoding image data supplied from an encoding apparatus by using encoding parameters supplied therefrom, and to an image processing system and method for decoding a bit stream to generate image data, for generating encoding parameters for use in encoding the image data again and encoding image data supplied from a decoding apparatus by using encoding parameters supplied therefrom.
When a conventional system re-encodes an image signal encoded by an MPEG (Moving Picture Expert Group) system, the image signal re-encoded may be deteriorated in terms of image quality. One of the reasons for this deterioration is the discrepancy between the encoded signal and the re-encoded signal, with regard to some parameters, i.e., picture type, moving vector and the like.
An example of the deterioration of image quality, which has resulted from the change in the picture type, will be explained. Assume that there is a picture type of an input decoded image for one GOP (Group of Pictures). The GOP may consists of, for example, nine pictures (N=9)
B
0
, B
1
, I
2
, B
3
, B
4
, P
5
, B
6
, B
7
and P
8
that are based on the MPEG system. More precisely, the GOP consists of an I (Intra) picture, P (Predictive) pictures and B (Bidirectionally predictive) pictures.
Every three pictures (M=3) make one sub-group which begins with either an I picture or a P picture and which is followed by an I picture or a P picture. To lock this GOP in terms of phase, as shown below, the I picture contained in the input decoded image is used as the reference image, without being modified at all.
B
0
, B
1
, I
2
, B
3
, B
4
, P
5
, B
6
, B
7
, P
8
Consider another picture type of an input decoded image for the following GOP, which is not phase-locked:
B
0
, I
1
, B
2
, B
3
, P
4
, B
5
, B
6
, P
7
In this GOP, the third picture (B
2
), which is a B picture that may be greatly deteriorated in image quality, is used as the reference image in the process of encoding the image signal again. Consequently, the accuracy of re-encoding decreases, inevitably causing a great deterioration of image quality.
In the conventional encoders, not only the picture type, but also another coding parameter, e.g., the motion vector, may be maintained unchanged after the image signal is encoded again. If so, the image quality will deteriorate less than in the case where the values of the coding parameters, which have been calculated during the process of re-encoding the image signal are used. In the conventional encoders, all coding parameters, including the picture type and the motion picture, are maintained unchanged after the image is encoded again, whereby the quality of the image represented by the image signal encoded again scarcely deteriorated.
Errors may be added to the bit stream in the transmission path. The encoder that has encoded the original bit stream may use coding parameters that do not accord with the MPEG standards. In either case, the bit stream the decoder has received may have a syntax error may in some cases.
If a syntax error is made in the bit stream, the decoder searches for the next start code (a 32-bit synchronization code), from the position where the error has occurred in the bit stream, thereby accomplishing error recovery. The decoder cannot decode the signal included in a part of a bit stream that extends between the start point of the error-occurring position and the start point of the error-recovering position. Hence, the decoder uses, instead of image signals lost, the image data already decoded to conceal an error resulting from the image signal that has been lost due to the syntax error. That is, the decoder copies, for example, an image displayed in the past, and the image copied is displayed for that part of the image, which has been lost due to the syntax error.
As describe above, the conventional encoder may re-encode a decoded image signal under the condition that the coding parameter applied before the re-encoding and the coding parameter applied after the re-encoding are identical in terms of picture type or motion vector. When the decoder receives a bit stream having a syntax error, it conceals the error and outputs the concealed image data to the re-encoder. Then, the re-encoder receives no coding parameters, or receives the coding parameter having an error, from the decoder. If the encoder encodes the image signal by using the erroneous coding parameters supplied from the decoder, the image represented by the encoded image signal will have its quality greatly deteriorated.
As indicated above, hitherto the encoder encodes a bit stream, in most cases, by using the coding parameters supplied from the decoder, no matter whether a syntax error has occurred or not in the bit stream input to the decoder. The encoder cannot process the bit stream signal in a normal way, because it uses the erroneous coding parameters to encode the bit stream.
BRIEF SUMMARY OF THE INVENTION
The present invention has been made in view of the foregoing. The object of the invention is to provide a decoding apparatus and method which can generate data indicating that an error has occurred in a bit stream, an encoding apparatus and method which can encode perform-n good data-encoding even if an error has occurred in a bit stream, and an image processing system and method.
A decoding apparatus according to the present invention, designed to achieve the object, comprises: decoding means for decoding an input bit stream to generate image data; parameter generating means for generating coding parameters of each layer, to be used to encode the image data again, which has been generated by the decoding means; and error flag generating means for generating an error flag which indicates whether the coding parameters generated for each layer by the parameter generating means can be effectively used to encode the image data again.
A decoding method according to the invention comprises: decoding an input bit stream to generate image data; generating coding parameters of each layer, to be used to encode the image data again; and generating an error flag which indicates whether the coding parameters generated for each layer can be effectively used to encode the image data again.
An encoding apparatus according to this invention comprises: parameter evaluating means for determining whether coding parameters for each layer, which have been input from a decoding apparatus, can be used effectively to encode image data input from the decoding apparatus, from an error flag that indicates whether the coding parameters can be used effectively; parameter calculating means for calculating coding parameters from the image data supplied from the decoding apparatus, in accordance with data supplied from the parameter evaluating means and indicating that the coding parameters are invalid; and encoding means for encoding the image data by using the coding parameters input from the decoding apparatus when the parameter-evaluating mean determines that the coding parameters supplied from the decoding apparatus are valid, and by using the coding parameters generated by the parameter calculating means when the parameter-evaluating mean determines that the coding parameters supplied from the decoding apparatus are invalid.
Another encoding apparatus according to the invention comprises: counting means for counting a number of times image data of a prescribed picture type is continuously input from a decoding apparatus; picture type changing means for generating coding parameters in accordance with data supplied from the counting means and indicating that the count of
Igi Nobuhiro
Kato Motoki
Narita Hideyuki
Obata Koji
Frommer William S.
Frommer & Lawrence & Haug LLP
Polito Bruno
Sony Corporation
Vo Tung
LandOfFree
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