Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
1998-07-02
2002-03-19
Rao, Andy (Department: 2713)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240170
Reexamination Certificate
active
06359929
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an image predictive decoding method of predictively decoding a compressed digital image and, more particularly, to an overlapped compensation method for interlaced images, an apparatus for performing the method, and a data storage medium for storing the method.
BACKGROUND OF THE INVENTION
Compressive coding is required to store and transmit a digital image efficiently. There have been proposed methods of compressively coding a digital image, such as DCT (Discrete Cosine Transform) represented by JPEG and MPEG, and waveform coding, i.e., sub-band coding, wavelet coding, and fractal coding. Further, in order to remove redundant signals between images, inter-image prediction using motion compensation is performed, and a difference signal is subjected to waveform coding.
MPEG, which is based on motion compensation DCT, will be described.
An input image to be processed is divided into a plurality of 16×16 macroblocks. Each 16×16 macroblock is further divided into 8×8 blocks. Each 8×8 block is subjected to DCT. The resulting transform coefficients are quantized and then, transmitted or stored. This is called intra-frame coding.
On the other hand, using a method of detecting motion, such as block-matching which matches blocks, a predictive macroblock, which has the least error to a target macroblock of a frame, is detected among macroblocks of another frame temporally adjacent to the former frame. Motion is also detected. An optimal predictive block is obtained by subjecting a previous image to motion compensation based on the detected motion. A signal indicating a predictive macroblock having the least error is a motion vector. An image to be referred for generating a predictive macroblock is a reference image.
Next, a difference between a target block among the 8×8 blocks into which the input image is divided, and its corresponding predictive block, is calculated. The difference is subjected to DCT, its transform coefficients are quantized, and the result is transmitted or stored along with motion information. This is inter-frame coding. At the receiver, the difference signal is restored from the quantized transform coefficients. Thereafter, a predictive block corresponding to the target block is calculated based on the motion vector transmitted or stored. The predictive block is added with the difference signal to reproduce the image.
MPEG
2
has two motion compensation modes for an interlaced image, i.e., a frame motion compensation mode and a field motion compensation mode. In the frame motion compensation, the data of an odd-numbered field and an even-number field of a block to be decoded are calculated based on the same motion vector. In the field motion compensation mode, the data of an odd-numbered field and an even-number field are obtained from two different motion vectors. In interlaced scanning, an odd-number field and an even-numbered field are scanned at different moments, so there is sometimes a large difference in the amount of motion between both of the fields. For this reason, when such an interlaced image is subjected to motion compensation, if an odd-numbered field and an even-number field are subjected to different motion compensation, the error of a predictive signal is made small, and resolution in the temporal region can be maintained.
On the other hand, according to the standard H.
263
established by ITU-T, as to motion compensation in decoding an image, a predictive block is generated in a way in which in addition to a motion vector of a target block to be decoded, motion vectors of blocks adjacent to the target block are used to produce predictive data, and the weighted average of the predicted data is calculated, which is a predictive block. This is called overlapped motion compensation. By the overlapped motion compensation, errors of a predictive signal to a target block and the predictive signals to all adjacent blocks are averaged, thereby suppressing the difference signal, and reducing distortion between blocks, i.e., a phenomenon where the border between two blocks is clearly perceivable, as observed in cases where motion compensation is performed block by block.
When the overlapped motion compensation is applied to an interlaced image, the error of a predictive signal is required to be small. However, the interlaced image is processed with the frame motion compensation mode and the field motion compensation mode, so that there is a case where to adjacent blocks are subjected to motion compensation with different modes. The frame motion compensation mode is effective for a static region in which a high-frequency component between scanning lines is small. The field motion compensation mode is suitable for a region having a large motion in which a high-frequency component between scanning lines is large. When a target block is processed with the frame motion compensation mode while the adjacent block is processed with the field motion compensation mode, because the predictive data calculated based on the motion vector of the adjacent block has a large high-frequency component between scanning lines, the overlapped motion compensation introduces a high-frequency component to the predictive signal of the target block. As opposed to this, when a target block is processed with the field motion compensation mode while the adjacent block is processed with the frame motion compensation mode, the averaging in the overlapped motion compensation reduces the temporal resolution of a predictive signal, thereby blurring a motion in the region having a large motion.
SUMMARY OF THE INVENTION
It is an object to provide an image predictive decoding method improving a coding efficiency by generating a highly efficient predictive signal when overlapped motion compensation is applied to an interlaced image, an apparatus for the method, and a data storage medium for the method.
Other objects and advantages of the present invention will become apparent from the detailed description desired hereinafter; it should be understood, however, that the detailed description and specific embodiment are desired by way of illustration only, since various changes and modifications within the scope of the invention will become apparent to those skilled in the art from this detailed description.
According to a first aspect of this invention, there is provided an image predictive decoding method including
a decoding method in which when decoding compressively coded image data resulting from predicting the data of a predictive region to a target region, using information about a plurality of motion compensation modes, and a plurality of motion vectors corresponding to the plurality of motion compensation modes, and performing coding, for a target region to be decoded, target predictive region data calculated based on the motion vector of the target region, and adjacent predictive region data calculated based on the motion vector of at least one adjacent region to the target region, are weightedly averaged to produce optimal predictive region data to the target region,
said image predictive decoding method calculating the adjacent predictive region data, which is calculated based on the motion vector of at least one adjacent region to the target region, based only on the motion vector of the adjacent region having the same motion compensation mode as the target region, to produce the optimal predictive region data.
Therefore, it is possible to suppress the error of a predictive signal by performing overlapped motion compensation to interlaced image while getting around the problems that the overlapped motion compensation introduces high-frequency components to a static region, and that the motion in a region having a large motion blurs due to a reduction in the temporal resolution of a predictive signal by averaging in the overlapped motion compensation.
According to a second aspect of this invention, there is provided an image predictive decoding method including
a decoding method in which when decoding
Parkhurst & Wendel L.L.P.
Rao Andy
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