Image analysis – Image compression or coding – Lossless compression
Reexamination Certificate
1999-05-07
2003-05-27
Mehta, Bhavesh M . (Department: 2625)
Image analysis
Image compression or coding
Lossless compression
C375S240230
Reexamination Certificate
active
06571019
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to coded block pattern (CBP) encoding and decoding in a video signal encoding and decoding system and more particularly to CBP encoding/decoding apparatus and method wherein one of variable length coding (VLC)/variable length decoding (VLD) table is stored in a memory and selectively applied for encoding and decoding a coded block pattern of a macroblock according to the number of blocks having object pixels within the macroblock, which is detected using shape information.
2. Description of Related Art
Generally, video signal compressive encoding and decoding allow not only transmission of video information via low rate channels, but also reduce memory requirements for storing the video. Therefore, compression encoding and decoding techniques are very important to the multimedia industry requiring applications such as storage and transmission of video.
Standardization of information compressing methods are required for compatibility of information and extension of the multimedia industry, while standards for video are established based upon various applications. Representative standards for video encoding and decoding are H.261 recommended by ITU-T (International Telecommunication Union-Telecommunication Standardization Sector, old CCITF) for transmitting video information for video phone and video conferencing via ISDN (Integrated Service Digital Network), H.263 recommended by ITU-T for transmitting the video information via PSTN (Public Switched Telephone Network), MPEG (Moving Picture Experts Group)-1 recommended by ISO/IEC JTC 1/SC29/WG11 (International Standardization Organization/International Electrotechnical Commission Joint Technical Committee 1/Sub Committee 29/Working Group 11) MPEG for storing video in digital storage media (DSM), and MPEG-2 for high definition digital broadcasting such as EDTV (Enhanced Digital Television) and HDTV (High definition Television).
Compressive encoding of still image signals also has been standardized and JPEG (Joint Photographic Coding Experts Group) recommended by ISO/IEC JTC1/SC29/WG1 is a representative standard.
Such conventional video signal coding methods encode a rectangular frame or a whole picture, thus called frame-based coding. This frame-based coding method encodes texture information (e.g., luminance and chrominance) of all picture elements (pels or pixels) forming the frame.
Recently, however, instead of coding and transmitting the whole frame, there are increased demands for multimedia products and service including a function of coding and transmitting or manipulating only a particular region (or object) that a user is interested in or wants for some necessities.
In response to this tendency, an object-based coding method of encoding an image in units of arbitrarily shaped regions has been actively studied as the alternative to the frame-based coding that encodes the whole frame.
FIG.
1
and
FIG. 2
show examples of test prior art images used for explaining the object-based coding.
FIG. 1
shows a frame including a picture of two children playing with a ball in a certain space (background). The object-based coding is appropriate for this case since only the video information is needed for transmission of an object composed of children and a ball. Namely, only texture information values of pixels forming the children and ball are encoded and transmitted. Here, the region including the children and ball is called an object and the other region, excluding the object, is called a background.
For compressively encoding the image shown
FIG. 1
using the object-based coding, an encoder and a decoder should equally recognize which pixels of the whole frame of pixels represent the children and ball and which pixels of the whole frame pixels represent the background. Such information is called shape information. The encoder should efficiently encode and transmit the shape information to the decoder to permit the decoder to recognize the shape information. The largest difference between the frame-based encoder/decoder and the object-based encoder/decoder is that the object-based encoder/decoder includes a shape information encoder/decoder.
FIG. 2
shows shape information when only the children and ball are considered as an object among the video information. The pixels forming the children and ball have bright values and the pixels forming the background have dark values.
In order to discriminate the pixels forming the object from the pixels forming the background, as shown in
FIG. 2
, the pixels are represented by shape information having predetermined values according to their respective regions. This is called a binary mask. For example, all the pixels belonging to the background have a value “0” and all the pixels belonging to the object have a value “255”, so that each pixel has one value between “0” and “255”. For the object-based coding, the shape information for identifying and discriminating object pixels and background pixels among all the pixels forming a whole picture is required. Each of the object pixels has the texture information.
The shape information can be represented by a contour indicating a boundary between the background and the object other than the binary mask. The two types are alternative. Contour extraction is carried out to express the binary mask as contour information. Altematively, contour filling is carried out to obtain the binary mask from the contour information. For the purpose of encoding and transmitting to the decoder the shape information with the small amount of bits, an effective shape information coding method is required. This shape information coding method is not related to the present invention, so the detailed description is omitted.
Representative frame-based coding methods are H.261 and H.263 recommended by ITU-T, MPEG-1 and MPEG-2 by ISO/IEC JTC1/SC29/WG11, and JPEG by ISO/IEC JTC1/SC29/WG1. Representative object-based coding methods are MPEG-4 recommended by ISO/IEC JTC1/SC29/WG11 and JPEG2000 by ISO/IEC JTC1/SC29/WG1.
A conventional video signal coding method that is widely used around the world is transform coding. Transform coding converts video signals into transform coefficients (or frequency coefficients) to suppress transmission of high frequency components and to transmit signals of low frequency components. This method has an advantage of increasing a compression ratio with reduction of loss in picture quality. Discrete Fourier transform (DFT), discrete cosine transform (DCT), discrete sine transform (DST), and Walsh-Hadamard transform (WHT) have been developed for the transform coding.
The DCT of the transform methods is excellent at compacting video signal energy into a low-frequency component. Compared with other transform methods, DCT provides high picture quality with only the small number of low frequency coefficients and includes a fast algorithm. Due to these advantages, DCT is the most generally used transform coding and is employed for the video coding standardization systems such as H.261, H.263, MPEG-1, MPEG-2, MPEG-4, and JPEG.
Conventional frame-based coding divides a frame into macroblocks, each respectively having 16 pixels in length and width (hereinafter this size is expressed as 16*16), while carrying out the coding in macroblock units. Namely, motion estimation, motion compensation, and coding type decisions are carried out in macroblock units. The coding type determines whether to encode an input video signal or perform motion compensation of an error signal of the macroblock. A macroblock corresponding to the former is called an intra macroblock and a macroblock corresponding to the latter is called an inter macroblock.
According to conventional techniques, DCT is performed with respect to input determined in accordance with the transmitted coding type and transform coefficients. Here, the macroblock is divided into blocks of 8*8 and the DCT is performed in block units.
FIG. 3
is part of the prior art and shows the relationship between a macroblock and bloc
Chun Sung-Moon
Chung Jae-Won
Kim Jae-Kyoon
Lee Jin-Hak
Moon Joo-Hee
Blakely Solokoff Taylor & Zafman
Hyundai Curitel, Inc
Mehta Bhavesh M .
Patel Kanji
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