Coded data generation or conversion – Digital code to digital code converters – To or from variable length codes
Reexamination Certificate
2000-02-14
2001-11-06
Young, Brian (Department: 2819)
Coded data generation or conversion
Digital code to digital code converters
To or from variable length codes
Reexamination Certificate
active
06313767
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a decoding apparatus which decodes a variable-length code such as a Huffman code.
BACKGROUND OF THE INVENTION
In recent years, a still-picture digital signal compression technique, JPEG (Joint Photographic Experts Group) and a moving-image digital signal compression technique, MPEG (Moving Picture Experts Group) are known as global standard techniques.
In these compression techniques, an image signal is orthogonally transformed by using DCT (Discrete Cosine Transformation), and subjected to the Huffman coding. Among the frequency components after the orthogonal transformation, the information of high frequency components are reduced, and further, in the Huffman coding, among the information representing these frequencty components, a longer Huffman code is allocated to information with lower probability of occurrence, while a shorter Huffman code is allocated to information with higher probability of occurrence. In this manner, the amount of data of the original image signal can be reduced.
Further, a known method in a Huffman-code decoding apparatus is to store decoded values from respective Huffman codes in a decoded value memory in advance, then when a Huffman code to be decoded is inputted, interpret the code length corresponding to the Huffman code and the priority order of the Huffman code in a Huffman code group having the code length, then read an actual address value in the decoded value memory containing the Huffman-code decoded values from an address memory corresponding to the code length, and read a decoded value for the Huffman code from a predetermined position of the decoded value memory in accordance with the address value and the priority order.
However, in the conventional Huffman-code decoding method, as the actual address values in the above-described decoded value memory are stored in the address memories corresponding to the respective code lengths, the entire capacity of the address memory is large.
SUMMARY OF THE INVENTION
The present invention has been made in consideration of the above situation, and has its object to efficiently store information to determine an address value to read a decoded value for a variable-length code from a decoded value memory.
Further, another object of the present invention is to store an address value in a memory, not as an actual address value of a decoded value memory, but as data in a form to be efficiently generated as the address value.
According to the present invention, the foregoing object is attained by providing a decoding apparatus comprising: first storage means for continuously storing decoded values for variable-length codes of the same code length; second storage means for storing an initial address in the first storage means; third storage means for storing offset values between the initial address in the first storage means and addresses for storing decoded values for variable-length codes of respective code lengths, respectively; first specification means for specifying a code length of an input variable-length code; second specification means for specifying the order of the input variable-length code among variable-length codes belonging to the specified code length; and address generation means for generating an address to read a decoded value from the first storage means, based on the offset value corresponding to the code length specified by the first specification means and the order specified by the second specification means.
Otherwise, the foregoing object is attained by providing a decoding apparatus comprising: first storage means for continuously storing decoded values for variable-length codes of the same code length; second storage means for storing plural data each on the number of variable-length codes belonging to each code length; first specification means for specifying a code length of an input variable-length code; second specification means for specifying the order of the input variable-length code among variable-length codes belonging to the specified code length; generation means for generating an accumulated value obtained by accumulating the plural data on the numbers of codes stored in the second storage means based on the code length specified by the first specification means; and address generation means for generating an address to read a decoded value from the first storage means based on the accumulated value and the order specified by the second specification means.
Other objects and advantages besides those discussed above shall be apparent to those skilled in the art from the description of a preferred embodiment of the invention which follows. In the description, reference is made to accompanying drawings, which form a part thereof, and which illustrate an example of the invention. Such example, however, is not exhaustive of the various embodiments of the invention, and therefore reference is made to the claims which follow the description for determining the scope of the invention.
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Aoki Koji
Ishizuka Keiji
Tateno Tetsuya
Canon Kabushiki Kaisha
Fitzpatrick ,Cella, Harper & Scinto
Nguyen John
Young Brian
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