Pulse or digital communications – Bandwidth reduction or expansion – Television or motion video signal
Reexamination Certificate
2000-11-21
2003-10-07
Le, Vu (Department: 2613)
Pulse or digital communications
Bandwidth reduction or expansion
Television or motion video signal
C375S240240, C382S237000
Reexamination Certificate
active
06631161
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and system for compressing motion image information with a high compression ration and at a high speed.
2. Description of the Related Art
In earlier image signal transmission, an image signal is first converted to another signal and then coded by assigning proper codes selected according to the statistical feature of the converted signal. When the image has high redundancy within a frame, as is the case with an image including a regular pattern or a plain image, there is a high correlation between adjacent pixels, and thus it is possible to predict, to a certain degree, a pixel value to be coded next from a pixel value which has already been coded. Therefore, if components which could not be predicted are extracted, the coding is performed only for those components which could not be predicted, thereby it becomes possible to compress information with a large compression ratio. This technique is called the predictive coding.
In the case of a motion image in a video telephone or the like, images of adjacent frames are very similar to each other, and thus the temporal change is limited. Such temporal redundancy can be removed by means of interframe predictive coding on the basis of interframe prediction. In this case, a block code is generally employed in which one codeword is assigned to one symbol, and one frame is divided into a plurality of pixel blocks so that the luminance difference within each block becomes smaller than within the entire frame. The smaller luminance difference within each block allows compression of information. This technique is called block coding.
Entropy coding is known in the art as a coding technique, which achieves data compression by assigning a high efficiency code to the converted signal. Huffman coding is known as a method for generating a high efficiency code. A representative example of the high efficiency code is an arithmetic code in which a probability numeric line is divided into segments in accordance with the occurrence probability of a symbol system, and a binary decimal number indicating a location in a segment is employed as a code for the symbol system. Codewords are generated one by one by performing the arithmetic process described above.
A three-step block coding system is known in the art as a technique for coding an image signal in an efficient manner. This technique consists of three steps: sampling; conversion; and quantification. In this technique, in order to retain a two-dimensional resolution and high-frequency components of a given image signal, it is generally required to perform sampling at a frequency twice the highest frequency component.
SUMMARY OF THE INVENTION
However, in the conventional image signal compression technique, because the complicated block coding process is employed, it is difficult to compress image data by means of predictive coding with a high compression ratio and at a high speed.
When differential information is compressed in the motion image compression process, that is, when successive values A
1
and A
2
are predicted to be similar to each other and when the value A
1
is known before the value A
2
occurs, the difference A
2
-A
1
is regarded as having a value near 0, and compression is performed using the conventional Huffman code or arithmetic code. However, if A
1
and A
2
can each take one of values 0, . . . , n, the difference A
2
-A
1
can have one of 2n+1 values. As a result, it is required to prepare 2n+1 Huffman code words. However, A
2
can actually take one of n values, and thus n codes are not used from the local point of view. This circuit that the code includes a large amount of redundancy.
In view of the above problems in the conventional techniques, it is an object of the present invention to provide a method and a system for compressing motion image information by means of predictive coding with a high compression ratio and at a high speed.
According to an aspect of the present invention, there is provided a method of compressing motion image information by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information thereby reducing redundant information between frames, the method including the steps of: comparing corresponding pixels to each other between frames, detecting an area where the absolute values of pixel differences are greater than a given parameter, and storing the detected area and the other area into the form of a 1-bit bit map; and compressing information in the area where the absolute values of pixel differences are greater than the parameter.
According to another aspect of the present invention, there can be provided a method of compressing motion image information by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information thereby reducing redundant information between frames, the method including the steps of: comparing corresponding pixels to each other between frames, detecting an area where the absolute values of pixel differences are greater than a given parameter, and storing the detected area and the other area into the form of a 1-bit bit map; and compressing information in the area where the absolute values of pixel differences are greater than the parameter and processing (deleting) the other area, where the absolute values of pixel differences are not greater than the parameter, as an area where there is no change in pixel value between frames. In this case, the 1-bit bit map information stored in the bit map information storage may be compressed by means of a binary image coding method such as a run length, modified READ (MR, MMR), modified Huffman (MH), or JBIG coding method. Further, the information in the area where the absolute difference values are greater than the given parameter may be compressed by means of an adaptive Huffman coding process including a plurality of Huffman tables as the amount of predicted information.
According to still another aspect of the present invention, there is provided a system for compressing motion image information, including entropy coding means or circuit for reducing redundant information between frames by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information, the system including: bit map information storage means or circuit for comparing pixels t and corresponding pixels t−1 to each other between frames pixel by pixel, detecting an area where the absolute values of pixel differences are greater than a given parameter, and storing the area and the other area into the form of a 1-bit bit map; and information compression means or circuit for compressing information in the area indicated, by the bit map stored in the bit map information storage circuit, as being greater in the absolute difference value between pixels t and t−1 than the parameter P.
According to still another aspect of the present invention, there is provided a system for compressing motion image information, including entropy coding means or circuit for reducing redundant information between frames by means of comparing spatially or temporally adjacent pixels to each other and outputting differential information, the system including: bit map information storage circuit for comparing pixels t and corresponding pixels t−1 to each other between frames pixel by pixel, detecting an area where the absolute values of pixel differences are greater than a given parameter, and storing the area and the other area into the form of a 1-bit bit map; and information compression means or circuit for compressing information in the area indicated, by the bit map stored in the bit map information storage circuit, as being greater in the absolute difference value between pixels t and t−1 than the parameter P, and for processing (deleting) pixels in the other area as those having no change between frames.
Preferably, the 1-bit bit map information stored in the b
Kajiki Noriko
Tanabe Satoshi
Kabushiki Kaisha Office NOA
Le Vu
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