Image analysis – Image transformation or preprocessing – Combining image portions
Reexamination Certificate
1999-02-24
2001-05-08
Couso, Yon J. (Department: 2623)
Image analysis
Image transformation or preprocessing
Combining image portions
C382S236000, C382S298000
Reexamination Certificate
active
06229930
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to image processing apparatuses, image processing methods, and data storage media and, more particularly, to an apparatus and a method for efficiently coding a transparency signal, an apparatus and a method for decoding a transparency signal coded by the coding apparatus or method, and a data storage medium containing a program implementing the transparency signal coding method or decoding method by software.
In the present invention, a transparency signal indicates the composition ratio when an image signal corresponding to a specific object and another image signal are composited, with individual images (objects) as components of a composite image being units.
BACKGROUND OF THE INVENTION
In recent years, we have greeted the age of multimedia in which audio, video and other data are integrally handled, and the conventional information media (i.e., means for transmitting information to men), such as newspapers, magazines, televisions, radios, and telephones, have been adopted as the subjects of multimedia. Generally, “multimedia” means to represent, not only characters, but also diagrams, speeches, and especially images simultaneously in relation with each other. In order to handle the conventional information media as the subjects of multimedia, it is necessary to transform the information into a digital format.
When the quantity of data possessed by each information medium described above is estimated as the quantity of digital data, in case of characters, the data quantity for each character is 1-2 byte. However, in case of speech, the data quantity is 64 kbits per second (quality for telecommunication) and, in case of moving picture, it is more than 100 Mbits per second (quality for current television broadcasting). So, as for the information media described above, it is not practical to handle such massive data as it is in the digital format. For example, although visual telephones have already been put to practical use by ISDN (Integrated Services Digital Network) having a transmission rate of 64 kbps-1.5 Mbps, it is impossible to transmit an image of a television camera as it is by the ISDN.
So, data compression technologies are demanded. In case of visual telephones, the moving picture compression technologies standardized as H.261 and H.263 by ITU-T (International Telecommunication Union-Telecommunication Sector) are employed. Further, according to the data compression technology based on MPEG
1
, it is possible to record image data, together with audio data, in an ordinary music CD (compact disk).
MPEG (Moving Picture Experts Group) is an international standard of data compression for data of a moving picture (an image signal of a moving picture). In MPEG
1
, data of a moving picture is compressed to 1.5 Mbps, i.e., data of a television signal is compressed to about 1/100. Since the transmission rate to which MPEG
1
is directed is limited to about 1.5 Mbps, MPEG
2
is standardized to meet the demand for higher image quality. In MPEG
2
, data of a moving picture is compressed to 2-15 Mbps. Under the existing circumstances, standardization of MPEG
4
is now proceeded by the working group for standardization of MPEG
1
and MPEG
2
(ISO/IEC JTC1/SC29/WG11). MPEG
4
enables coding and signal processing in object units, and thereby realizes new functions required in the age of multimedia. MPEG
4
has originally aimed at standardization of a coding method at a low bit rate, but the aim of standardization is now extended to a more versatile coding process at a high bit rate adaptable to an interlaced image.
In MPEG
4
, display of a composite image based on a coded image signal obtained by coding an image signal in object units, is realized by the following processes: decoding coded image signals corresponding to predetermined objects to generate decoded image signals; compositing the decoded image signals corresponding to the predetermined objects to generate a composite image signal; and reproducing the composite image on a screen, such as a monitor, based on the composite image signal.
The image composition process (the process of compositing the decoded image signals) is to superpose image signals corresponding to a foreground image which is an image of an object to be composited (target image) and a background image such that the foreground image lies on the background image when displayed.
To be specific, a color signal corresponding to the foreground image and a color signal corresponding to the background image are added at a predetermined weighting ratio, thereby obtaining a color signal corresponding to a composite image. The weighting ratio of the color signal of the foreground image is the transparency of the foreground image. A transparency signal of the foreground image is composed of transparency values of pixels composing the foreground image. A color signal is composed of a luminance signal and a chrominance signal. The luminance signal includes brightness information indicating the brightness of each of pixels composing the foreground image or the background image. The chrominance signal includes color information indicating the color (tone) of each of pixels composing the foreground image or the background image.
Further, in MPEG
4
, the transparency value is expressed by a numerical value of 8 bits. That is, the transparency value of a completely transparent pixel is “0”, and the transparency value of a completely opaque pixel is “255”. The transparency is expressed in 2
8
ways (256 gradations).
The value of each pixel (pixel value) of the color signal corresponding to the composite image is represented by formula (1).
Ycom=
(255
−Gfg
)×
Ybg+Gfg×Yfg
(1)
where Ybg is the pixel value of the background image, Yfg is the pixel value of the target (foreground) image, Gfg is the transparency value of the target image, and Ycom is the pixel value of the composite image.
By the way, in an object image signal produced by chromakey in a broadcast studio or the like, its pixel value Yfg has already been multiplied by the transparency value Gfg in many cases. Such a pixel value of the target image is expressed by Y′fg. Since
Y′fg=Gfg×Yfg,
the pixel value Ycom of the composite image is defined by formula (2).
Ycom=(
255
−Gfg
)
Ybg+Y′fg
(2)
Hereinafter, the process of displaying a composite image will be schematically explained by using FIGS.
7
(
a
)-
7
(
e
),
8
(
a
)-
8
(
d
), and
9
(
a
)-
9
(
d
).
FIG.
7
(
a
) shows an image space Sb including a background image Tb obtained from a color signal of a background, and FIGS.
7
(
b
) and
7
(
d
) show image spaces Sf
1
and Sf
2
including first and second target images Tf
1
and Tf
2
obtained from color signals of first and second foregrounds, respectively. Further, FIGS.
7
(
c
) and
7
(
e
) show image spaces Sg
1
and Sg
2
including first and second target images Gf
1
and Gf
2
obtained from transparency signals of the first and second foregrounds, respectively.
FIG.
8
(
d
) shows an image space Sc
13
including a composite image Tc
13
obtained by compositing the first target image Tf
1
(FIG.
7
(
b
)) and the background image Tb (FIG.
7
(
a
)) according to formula (1) or (2), and FIG.
9
(
d
) shows an image space Sc
23
including a composite image Tc
23
obtained by compositing the second target image Tf
2
(FIG.
7
(
d
)) and the background image Tb (FIG.
7
(
a
)) according to formula (1) or (2).
In MPEG
4
, coding and decoding of a transparency signal is performed object by object, by referring to a shape signal indicating whether each pixel value corresponds to a pixel positioned inside the object (hereinafter, referred to as an inside-object pixel) or a pixel positioned outside the object (hereinafter, referred to as an outside-object pixel). Further, coding and decoding of a transparency signal corresponding to each object are performed in units of rectangle regions (macroblocks) each comprising 16×16 pixels, into which an object regi
Couso Yon J.
Matsushita Electric - Industrial Co., Ltd.
Parkhurst & Wendel L.L.P.
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