Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1999-12-27
2002-12-10
Le, Vu (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240130, C375S240260
Reexamination Certificate
active
06493392
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates in general to the coding and decoding of a digital interlaced moving image or video, and more particularly to a method for coding and decoding a digital interlaced moving video, in which the digital interlaced moving video is compression-coded and transmitted with a degradation resulting from a transmission error or channel error being minimized, so that a moving picture of high quality can be reconstructed.
2. Description of the Prior Art
A scanning system for a digital moving video may generally be classified into a progressive type and an interlaced type. In the progressive scanning system, as shown in
FIG. 1
a,
a video frame or picture (these two terms will hereinafter be used together to mean the same thing) is constructed by obtaining and scanning all pixels in the frame at the same time. In the interlaced scanning system, as shown in
FIG. 1
b,
the pixels in the frame are partitioned into a top field as indicated by solid lines and a bottom field as indicated by dotted lines. The pixels in the top and bottom fields are obtained and scanned at different times. Namely, in the interlaced scanning system, a video frame is constructed by alternately obtaining and scanning each pixel line of the top field and each pixel line of the bottom field as indicated by the mixed solid and dotted lines.
In the interlaced scanning system, as shown in
FIG. 1
b,
there is a time difference between the top and bottom fields. In
FIG. 1
b,
the top field is shown to be earlier in time than the bottom field. But, the bottom field may be earlier in time than the top field in some cases. Due to such a time difference between the top and bottom fields, there may be different signal characteristics between adjacent scanning lines in the interlaced video frame. In other words, in the interlaced video frame, a signal characteristic of an with scanning line may be different from that of an (i+1)th or (i−1)th scanning line. However, the signal characteristic of the ith scanning line may be relatively high in correlation with that of an (i+2)th or (i−2)th scanning line in the same field, obtained at the same time. This phenomenon becomes more conspicuous as the motion of an object or objects on a video screen becomes larger in scale. For this reason, in the case where video coding techniques developed according to progressive video characteristics, such as motion estimation, motion compensation and discrete cosine transform (DCT), are applied to the coding of a video with interlaced video characteristics, a coding efficiency or coding gain is reduced.
In order to overcome such a coding efficiency reduction, research has been done for interlaced coding techniques such as field-based motion estimation, field-based motion compensation and adaptive field/frame DCT. Herein, coding methods developed on the basis of an interlaced video will hereinafter be referred to as “interlaced coding methods”, and coding methods developed on the basis of a progressive video will hereinafter be referred to as “progressive coding methods”.
The above interlaced coding techniques are included in the Moving Picture Experts Group Phase 2 (MPEG-2) standard which is prescribed for applications such as a digital television (TV) in International Standardization Organization/International Electrotechnical Commission Joint Technical Committee 1/Sub Committee 29/Working Group 11 (ISO/IEC JTC1/SC29/WG11) associated with digital moving video coding methods, and thus often utilized in actual application products.
On the other hand, widely used in digital moving video coders is a method wherein frames of a digital 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. 2
, which shows an example of picture coding types and the associated predictive directions. In
FIG. 2
, 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. Although the B frames utilize the motion compensated prediction like the P frames, they are highest in compression ratio 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 video, a digital order and coding order thereof will be different. For example, as shown in
FIG. 2
, 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 video is compression-coded and transmitted on the basis of only the I and P frames with no B frame.
The example of
FIG. 2
is applied to both a progressive video and interlaced video. But, in the interlaced video, each frame is constructed by interleaving each scanning line of one of the two fields between two adjacent scanning lines of the other field as shown in
FIG. 1
b.
Except for this fact, the video construction, predictive directions, etc. are applied in the same manner to the two types of videos.
For the compression-coding of a digital 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
Chung Jae-Won
Kim Jong Deuk
Moon Joo-Hee
Hyundai Electronics Industries Co,. Ltd.
Jacobson & Holman PLLC
Le Vu
Senfi Behrooz
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