Image analysis – Image compression or coding – Interframe coding
Patent
1996-12-19
1998-10-27
Couso, Jose L.
Image analysis
Image compression or coding
Interframe coding
382236, G06K 936
Patent
active
058287876
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an encoding apparatus and an encoding method of a motion image using a motion compensation.
BACKGROUND ART
A motion image encoding method represented by the MPEG (Moving Pictures Expert Group) standard has been known. In the MPEG, a GOP (Group of Pictures) structure which is constructed by a plurality of picture plane data is used. A random access can be executed on a unit basis of the GOP. In the MPEG, an I picture, a P picture, and a B picture are specified as picture coding types.
The I picture is an abbreviation of an Intra-Picture and denotes an intraframe encoded image. In the I picture, the whole picture plane is intra-encoded and is encoded in accordance with the same order as that of the original image. The P picture is an abbreviation of a Predictive-Picture and denotes an interframe forward direction predictive encoded image. That is, it is an image which is motion compensation predicted from a past image. There is also a case where the P picture includes an intra-encoded portion of a small block unit in the picture plane and it is encoded in accordance with the same order as that of the original image. The B picture is an abbreviation of a Bidirectionally Predictive-Picture and is a bidirectional predictive encoded image. That is, it is an image which is motion compensation predicted from past and future images. There is also a case where the B picture includes the intra-encoded portion of the small block unit in the picture plane.
It is assumed that at least one I picture is included in the GOP. One GOP is constructed by N, for example, 15 pictures (a time of 0.5 second) and the I picture or the P picture appears at every period M, for example, 3. Although the values of N and M are not specified, practically, a value corresponding to 0.4 second to several seconds is chosen for N and a value corresponding to about 3 to 6 is chosen for M. In the MPEG1, it is specified that the beginning of the GOP is the I picture on a bit stream and the last of the GOP in the order of the original picture plane is the I or P picture.
FIG. 6 shows a process when a sequence which continues with respect to the time is encoded by changing M in the above-mentioned MPEG encoding method. It is necessary to change M in case of continuously encoding image data of a television system in which frame frequencies are different such that they are equal to, for example, 25 Hz (in case of the television system such as a PAL system or the like) and 30 Hz (in case of the NTSC system). As another example, M is changed in the sequence even when two data of different M numbers are combined by an edition of a GOP unit.
FIG. 6 shows an example in which image signals of (M=2) and (M=3) are combined and a video input indicates an original image. CUR.sub.-- M expresses the number of M for the present frame. Codes of B, I, and P denote the above-mentioned picture coding types.
In an encoding process of the B picture, after the I and P pictures were first processed, the B picture which is inserted between the I and P pictures is encoded. Consequently, the order of the pictures of the encoding process is different from the order (display order) of the original image. That is, no frame delay is given to the picture of the I or P type and a delay of the number of frames instructed by CUR.sub.-- M is given to the picture of the B type, thereby allowing the picture of the B type to be inserted between pictures of the I or P type. "Present of MC (motion compensation)" in FIG. 6 shows the order which is rearranged from the order of images to the order (coding order) of encoding process as mentioned above.
In FIG. 6, the picture expressed as "MC forward direction" shows a past picture for the picture of the coding order and is used for a forward direction prediction. For example, for a picture shown by 4P, the past picture is 3I and a forward direction prediction is executed by using the picture 3I. A picture expressed as "Reverse direction of MC" shows a future picture for the picture of the c
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Couso Jose L.
Frommer William S.
Sony Corporation
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