Computer graphics processing and selective visual display system – Computer graphics processing – Animation
Reexamination Certificate
1997-07-25
2001-09-18
Vo, Cliff N. (Department: 2671)
Computer graphics processing and selective visual display system
Computer graphics processing
Animation
Reexamination Certificate
active
06292199
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The invention relates to a method for coding and decoding digitized frames of a special effects film and devices for coding and decoding digitized frames of a special effects film.
2. Prior art
The invention is based on a method for coding digitized frames of a special effects film of the generic type of the independent claim
1
.
Previously known coding methods for full-motion pictures are usually defined with relatively few options. The MPEG2 standard has already begun to change this situation since it already allows a relatively large number of optional configurations.
For future standards for coding full-motion pictures, it is desirable that they should allow even more flexibility, making it possible to adapt the coding parameters to the characteristics of the picture material to be coded to an even greater degree than hitherto. In this connection, special parameters for classes of video signals can then also be taken into account which do not occur particularly frequently but can be coded much better by a special choice of parameters.
Such a class of video signals are stroboscope-like alternations of frames from two frame sequences which, for example, occur frequently in the case of music video clips. In such a special effects film, a first number of frames of a first film scene is followed in succession by a second number of a second film scene. As a result of this, frequent scene edits, which in each case provide a completely new picture content, occur in this special effects film. Such a special effects film is digitized and then coded in accordance with the familiar MPEG2 standard, the frequent scene edits cause a high volume of data at the output of the coding device. This is due to the fact that the coding device cannot perform any redundancy compression in the first frame after the scene edit due to a successful motion estimation for various macroblocks of the frame. Thus, a large number of so-called intracoded macroblocks are produced which are coded without temporal prediction in the first frame. Compared with unidirectionally or bidirectionally predictively coded blocks, the data volume of these macroblocks is much larger. In the case of the unidirectionally or bidirectionally predictively coded blocks, only the difference between the macroblock to be transmitted and the motion-compensated macroblock is coded.
SUMMARY OF THE INVENTION
The object of the invention is to specify a coding method for the special effects film described, in which the data volume is greatly reduced in spite of the frequent scene edits occurring. For this purpose, only a small change is necessary in a coding method such as, for example, MPEG2, the hardware complexity remaining virtually unchanged.
According to the invention, the two frame buffers in the coding device are controlled separately. The two frame buffers are operated in such a manner that in each case one frame buffer is used for predicting the frames of the first film scene and the other frame buffer is used for predicting all frames of the second film scene. If no prediction takes place, both frame buffers are used for the bidirectional prediction of one frame of one of the two film scenes. Compared with the method known from the prior art, this method has the advantage that when scene changes occur, the last frame of the film scene to which the switch-over is carried out, still stored in one of the frame buffers. As a result, a motion estimation can in turn be performed for the new frame to be coded on the basis of the last frame in the frame buffer. Thus, intracoded macroblocks do not necessarily occur, even after a scene edit, and the data volume is considerably reduced.
It is particularly advantageous if only the so-called forward prediction is used for coding the frames of the special effects film. In forward prediction, the motion estimation for a frame to be coded is carried out with a reference frame which, chronologically, occurs before the frame to be coded in the sequence of frames which will be displayed later on a screen. The coding method is simplified by specifying forward prediction for the prediction mode. This is because it is not necessary to resort the frames for the coding process.
If both forward and backward prediction is to be permitted as prediction mode, it is advantageous if the frames are resorted so that the frames predicted backward are coded delayed in time and the frame from which the backward prediction is carried out, is cooled before the frames predicted backward. Such resorting has also been provided in the MPEG2 standard. In the case of a backward-predicted frame, the motion compensation for the frame to be coded is performed on the basis of a frame which, chronologically, is only displayed after the frame to be coded.
It is also advantageous if information specifying the frame buffer from which the frame is to be predicted, is inserted into the data stream for each predicted frame. This information corresponds to the information specifying which film scene the frame belongs to. A decoding device then knows immediately which frame buffer is to be used for the motion compensation.
It is additionally of advantage if information specifying that the frame belongs to a stroboscope-like special effects film sequence, is inserted into the data stream for each predicted frame. By means of this information, the decoding device can carry out a reconfiguration so that, for example, a mode is preset which allows only forward prediction or forward prediction and backward prediction.
Correspondingly, it is advantageous for a method for decoding coded frames which were coded in accordance with the method according to the invention, if the two frame buffers in the decoding device are operated separately so that again one and the same frame buffer is always used for predicting frames of the first film scene and the other frame buffer is used for predicting frames of the second film scene. This allows the coding device to code the frames motion-compensated, even after a scene change, so that the data volume for the coded frames is reduced.
In order to simplify the image processing in the decoding device, it can also be advantageous if only forward prediction is allowed for predicting frames of the stroboscope-like special effects film.
On the other hand, forward prediction or backward prediction can also be allowed, if a resorting according to the MPEG2 standard is carried out with respect to the order in which the frames are output, at least for the backward-predicted frames.
It is also advantageous if information which has been inserted into the data stream for the predicted w frames, is used for deciding the frame buffer from which the frame must be predicted. This eliminates the need for a complex analysing unit which independently determines the frame buffer from which the frame must be predicted.
Further advantageous measures for a device for coding digitized frames of a stroboscope-like special effects film are found in claims
10
to
15
. Advantageous measures for a device for decoding digitized frames of a stroboscope-like special effects film are found in claims
16
to
19
.
REFERENCES:
J. De Lameillieure, R. Schafer, “MPEG-2 Bildercodierung fur das digitale Fernsehen”, Fernseh-Uno Kino-Technik, 48. Nr. Mar. 1994, pp. 99-107.
D. Teichner, “Datenreduktionsverfahren im Bereich der Videoproduktion ” Fernseh-Uno Kinorwxhnik 49. Jahrgang Nr. Jun. 1995 Seiten 347-355.
Deutsche Thomson-Brandt GmbH
Herrmann E. P.
Kurdyla R. H.
Tripoli J. S.
Vo Cliff N.
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