Abstract: A data compression and decompression apparatus and method providing a high compression ratio. The data compressing apparatus includes, for example, an obtaining section, a first coding section, a first controlling section, a judging section, a second coding section, and a second controlling section. Characters are obtained one after another from a compression target. A code is then output corresponding to the character when the character and a predetermined number of characters are not identical. Subsequently, the number of characters obtained are counted when the character and the predetermined number of characters are identical, and a code corresponding to the number of characters counted is output when the character obtained is not identical with the predetermined number of characters.

Abstract: Data coding apparatus and decoding apparatuses to encode and decode data at a high speed. A data coding apparatus provided with a code table in which ranks and codes are made corresponding so that a code length becomes larger as the rank becomes lower. A rank holding unit is stored with a corresponding relationship between the character and the rank relative to each context. When the character to be encoded is input, the rank holding unit outputs a rank of that character relative to the context at that time, and the code corresponding to the rank within the code table is output by the rank coding unit. The data coding apparatus is constructed to change the rank of the character used for outputting within the rank holding unit up to a higher rank.

Abstract: The present invention provides a plurality of code tables such as a high-usage code table and a low-usage code table in an entropy coding unit, and transforms a block-sorted last character string from a block-sorting transforming unit into an MTF code string in an MTF transforming unit. The entropy coding unit switches the code tables at a discontinuous part of the MTF code string to perform entropy coding. In addition, the present invention stores reference lists, whose number is equal to the number of kinds of used characters, in a reference list memory. The MTF transforming unit selects a reference list corresponding to a first character of the block-sorted character string to perform an MTF transformation.

Abstract: An Adaptive Discrete Cosine Transformation is widely used for orthogonally transforming image data. The number of adders necessary for sum-of-product operations in a matrix multiplication is reduced. A high speed matrix multiplication and a progressive image build-up are realized by minimizing the number of operations by skipping those for insignificant data. This invention speeds up the operations for restoring image data, minimizes the necessary circuit size, and enables a progressive image build-up to be performed efficiently.

Abstract: A device for coding a series of symbols based on a multi-level arithmetic coding scheme includes a coding unit for coding the symbols based on frequency of occurrence of the symbols and orders of the symbols according to the frequency of occurrence, a context holding unit for storing the frequency of occurrence and the orders, a context updating unit for updating the frequency of occurrence and the orders upon receiving a control signal, and a controlling unit for sending the control signal when one of the symbols is coded and a cumulative frequency is less than a predetermined value, wherein the cumulative frequency is a sum of the frequency of occurrence for all of the symbols.

Abstract: A method and apparatus for encoding and decoding image data in which continuous still images are compressed and decompressed. The apparatus divides a plurality of multivalue image data into blocks each comprising a plurality of pixels, the pixels in the block are orthogonal converted and compressed, and the original image data is decompressed from the encoded data. The apparatus detects the block having an image change as an effective block. For a macro block including a plurality of effective blocks, a compressing order of the macro blocks is decided by the order according to appearance frequencies of the effective blocks or a predetermined order and the image data is compressed every macro block. As encoded data, the order information and code information of the macro block are sequentially transmitted. In this instance, the code amount is monitored. When the code amount exceeds a predetermined threshold value, the compression is stopped and the compression of the next image is performed.

Abstract: A designated field image is extracted instead of a frame image and only the effective block of the field image which was judged as a block having a change is also encoded. Block information and field information are added to the encoded block and the resultant data is transmitted as moving image code data. On the decompressing side, only the field image data separated from the moving image code data is decompressed and updated and the updated field is copied as another field which was not updated, thereby decompressing the image data of one frame. The field image data is alternately switched and encoded. Further, when a code amount increases, the same field as the previous frame is encoded. On the decompressing side, the updated field image data is copied to the field image data which is not updated and two field images are equalized, thereby preventing a visual deviation due to a difference between the field images.

Abstract: The present invention relates to an image data reconstructing apparatus for reconstructing an original image by dividing image data into a plurality of blocks each including N.times.N picture elements, performing two-dimensional orthogonal transform on each of said blocks, quantizing and encoding the result of said transform, decoding the encoded result, dequantizing and two-dimensional inverse orthogonal transforming the above result, wherein an operation associated with the multiplication is skipped if a multiplication by zero is detected when two-dimensional inverse orthogonal transform is performed. Before performing dequantization, two block volume of buffer is provided before or after performing two-dimensional inverse orthogonal transform for executing a pipeline process.