Image analysis – Image compression or coding – Predictive coding
Reexamination Certificate
1997-08-13
2001-08-14
Couso, Jose L. (Department: 2624)
Image analysis
Image compression or coding
Predictive coding
C382S236000, C386S349000, C348S419100
Reexamination Certificate
active
06275618
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for and a method of processing images, and a recording medium. More particularly, the present invention relates to an apparatus for and a method of processing images, and a recording medium with which images subjected to the MPEG (Moving Picture Experts Group) coding in the form of open GOP (Group Of Pictures) can be reproduced without changing image quality.
2. Description of the Related Art
In the MPEG coding, an image of a certain frame (field) is predicted from frames before and behind the frame so that random access can be made in units of GOP comprising several frames grouped together.
Meanwhile, the GOP is divided into a closed GOP in which prediction is performed by using only images belonging to itself, as shown in
FIG. 1A
, and an open GOP in which the first B-picture of a certain GOP is predicted by using not only an I-picture belonging to that GOP, but also a P-picture forming one image of the preceding GOP, as shown in FIG.
1
B.
On condition that a quantity of codes is kept the same, the closed GOP is inferior in image quality to the open GOP. Conversely, to obtain image quality by the closed GOP at the same level as obtained by the open GOP, a quantity of codes is increased. From the standpoints of improving image quality and reducing a quantity of codes, therefore, the open GOP is generally employed.
The open GOP has however accompanied a problem below. When image editing of, for example, inserting in one MPEG bit stream X shown in FIG.
2
(A) the other MPEG bit stream Y shown in FIG.
2
(B) is performed, image quality is remarkably deteriorated in hatched portions of the decoded images, shown in FIG.
2
(
c
), at the joint between the bit streams X and Y.
More specifically, of B-pictures of images forming one GOP, those B-pictures locating upstream of an I-picture in the same GOP (hereinafter referred to as before-I-picture B-pictures) are predicted in two-way directions from the I-picture and a P-picture as one of images forming the preceding GOP. When the other bit stream Y is joined to one bit stream X, therefore, each of the before-I-picture B-pictures in the first GOP of the bit stream Y is predicted by both backward prediction using an I-picture in that GOP (current GOP) and forward prediction using a P-picture in the last GOP (preceding GOP) of the bit stream X which has no relation with the bit stream X, as shown in FIG.
3
. This has raised a problem that block noises are generated and image quality is remarkably deteriorated.
To overcome such a problem, there is proposed a method of setting a broken link flag specified in the GOP layer, for example, in the bit stream after being edited, and causing an MPEG decoder to recognize that the bit stream has been edited. Then, the MPEG decoder does not display the before-I-picture B-pictures in the GOP for which the broken link flag is set, but continues to display the image prior to those before-I-picture B-pictures.
The MPEG decoder is however not always designed to be able to detect the broken link flag and hence cannot deal with all the cases.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an apparatus for processing images which can easily prevent deterioration in quality of images subjected to the MPEG coding in the form of open GOP.
To achieve the above object, an apparatus for processing images, according to the present invention, comprises GOP detecting means for detecting GOP's from a bit stream, picture-type detecting means for detecting the picture types of images forming each of the GOP's, and deleting means for deleting B-pictures of images forming one GOP in the bit stream, which are to be predicted by using one of images forming another GOP preceding the one GOP, in accordance with the detected picture types.
Also, a method of processing images, according to the present invention, comprises the steps of detecting GOP's from a bit stream, detecting the picture types of images forming at least one of the GOP's, and deleting B-pictures of images forming one GOP in the bit stream, which are to be predicted by using one of images forming another GOP preceding the one GOP, in accordance with the detected picture types.
Further, a recording medium according to the present invention records therein a bit stream deprived of B-pictures of images forming one GOP in the bit stream which are to be predicted by using one of images forming another GOP preceding the one GOP.
REFERENCES:
patent: 5521927 (1996-05-01), Kim et al.
patent: 5732183 (1998-03-01), Sugiyama
patent: 5751888 (1998-05-01), Fukuchi et al.
patent: 5754241 (1998-05-01), Okada et al.
patent: 5774206 (1998-06-01), Wasserman et al.
patent: 5838678 (1998-11-01), Davis et al.
Chang Dexter T.
Couso Jose L.
Do Anh Hong
Frommer William S.
Frommer Lawrence & Haug LLP.
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