Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-12-29
2002-07-16
Kelley, Chris (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
Reexamination Certificate
active
06421386
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to the coding and decoding of a digital moving image or video including gray scale shape information, and more particularly to a method for coding and decoding a digital moving video including gray scale shape information, in which the gray scale shape information is compression-coded and transmitted with a degradation in picture quality resulting from a transmission error or channel error being minimized.
2. Description of the Prior Art
Generally, video signal compression-coding and decoding methods are capable of transmitting video information through a low-rate channel and reducing the capacity of a memory required to store the video information. In this connection, the video signal compression-coding and decoding methods are very important techniques for the multimedia industry necessitating applications such as video storage and transmission. The present invention relates to a method for coding and decoding a digital moving video including gray scale shape information, which is applicable to such video signal compression-coding and decoding techniques.
In digital moving video coders, there is widely used a method wherein frames of a digital moving video are defined and used as three types, or I, P and B types for high-efficiency video compression and random access. Here, information for distinguishing the I, P and B frames from one another is defined as a “picture coding type”. Features of these three types of frames will hereinafter be described with reference to
FIG. 1
, which shows an example of picture coding types and the associated predictive directions. In
FIG. 1
, reference directions of P frames are indicated by the upper arrows and reference directions of B frames are indicated by the lower arrows. In this example, an interval between adjacent I frames and the number of consecutive B frames may be varied according to applications or equipment.
Firstly, the coding of I frames (intra coded frames) does not refer to other frames.
Secondly, the motion compensated prediction and coding of P frames (predictive coded frames) are performed with reference to a previous I frame or a previous P frame. As a result, the coding is possible at a high compression ratio. In this case, the referred I frame or P frame is defined as a “reference frame”. Between successive frames of a video, there is a high redundancy of texture information on a time axis. For this reason, a method of estimating motion information between a previous reference frame and a current P frame, performing motion compensated prediction using the estimated motion information and coding and transmitting a prediction error and the motion information is more advantageous in view of a compression rate than a method of performing the coding with no reference, like the I frame coding.
Thirdly, B frames (bidirectionally-predictive coded frames) are highest in compression rate. The prediction of the B frames is performed with reference to a next frame as well as a previous frame. The B frames are highest in compression rate because two reference frames are used and a more excellent one of prediction performances thereof is selected. On the other hand, the B frames do not become reference frames for other frames. In this connection, a previous frame of a current B frame is a previous I frame or P frame nearest to the current B frame in display order. Also, a next frame of the current B frame is a next I frame or P frame nearest to the current B frame in display order.
Provided that all the I, P and B frames are used for the compression-coding of a digital moving video, a digital order and coding order thereof will be different. For example, as shown in
FIG. 1
, the I, P and B frames are coded in order of I
1
, P
1
, B
1
, P
2
, B
2
, P
3
, B
3
, I
2
and B
4
, whereas they are displayed in order of I
1
, B
1
, P
1
, B
2
, P
2
, B
3
, P
3
, B
4
and I
2
. The second frame, B
1
, in the display order can be decoded and displayed in a receiver after the third frame, P
1
, in the display order is decoded in the receiver. In this regard, low-delay coding is required for an application with a real-time video communication function, such as a videophone. In such an application, a digital moving video is compression-coded and transmitted on the basis of only the I and P frames with no B frame.
For the compression-coding of a digital moving video, the motion estimation and compensation and the texture information coding are performed on the basis of a pixel group unit with a predetermined size, which is defined as a “macroblock (MB)”. The most widely used size of the macroblock is generally 16 pixels/line×16 lines (referred to hereinafter as 16×16).
Macroblock-unit coding methods may generally be classified into two types, or an “intra(frame) coding” method and an “inter(frame) coding”method. The intra coding method is adapted to code input texture information included in a macroblock, and the inter coding method is adapted to predict texture information from a reference frame and code a difference between the predicted texture information and input texture information, or a prediction error. Because the coding of an I frame is performed without referring to other frames, the intra coding method is performed with respect to all macroblocks in the I frame. But, the inter coding method as well as the intra coding method are possible with respect to a P frame. As a result, any one of either the inter coding method or intra coding method is selected for a higher coding efficiency. For example, in the case where the motion estimation is erroneously performed, the prediction error may become larger. In this case, coding the larger prediction error may be lower in coding efficiency than coding the input texture information. Hence, in this case, the intra coding method is more advantageous than the inter coding method. This signifies that some macroblocks for the intra coding may be present in the P frame.
In brief, the intra coding method and inter coding method are selectively performed according to whether signal to be coded is an input texture signal or a prediction error signal. Macroblocks for the intra coding and inter coding are together present in the P frame, whereas only macroblocks for the intra coding are present in the I frame.
Hereinafter, the macroblocks for the intra coding will be referred to as “intra macroblocks” and the macroblocks for the inter coding will be referred to as “inter macroblocks”. Also, information for distinguishing the intra and inter macroblocks from each other will be defined as a “macroblock type”.
On the other hand, moving video coding methods may generally be classified into a frame-based coding method which codes a rectangular frame and an object-based coding method which codes only an arbitrarily-shaped region. The object-based coding method is adapted to code and transmit only an object region to be coded, whereas the frame-based coding method is adapted to code and transmit all pixels in the frame. Because the object-based coding method is advantageous in that the user can code and transmit or manipulate only a desired object, it is anticipated to play an important part for the whole of future multimedia industry.
The representative examples of the framed-based coding method are shown in the H.261 and H.263 standards prescribed in International Telecommunication Union-Telecommunication Standardization Sector (ITU-T, the successor of CCITT) and the Moving Picture Experts Group Phase 1 (MPEG-1) and MPEG-2 standards prescribed in International Standardization Organization/International Electrotechnical Commission Joint Technical Committee 1/Sub Committee 29/Working Group 11 (ISO/IEC JTC1/SC29/WG11). The representative examples of the object-based coding method are shown in the MPEG-4 standard prescribed in ISO/IEC JTC1/SC29/WG11.
With reference to
FIG. 2
, there is a block diagram of an MPEG-4 moving video encoder established by the above international standardization organization
Chung Jae-Won
Kweon Ji Heon
Moon Joo-Hee
Hyundai Electronics Industries Co,. Ltd.
Kelley Chris
Vo Tung
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