Image coding method, image coding apparatus, image decoding method and image decoding apparatus

Abstract

An apparatus is provided for decoding last position information indicating a horizontal position and a vertical position of a last non-zero coefficient in a predetermined order within a current block to be decoded, the current block being included in a picture and including a plurality of coefficients. The apparatus includes one or more processors, a communication unit, and storage coupled to the one or more processors and the communication unit. The communication unit is configured to transmit a request for a bitstream to an external system, and receive the bitstream from the external system. The one or more processors are configured to obtain the bitstream, perform first arithmetic decoding, perform second arithmetic decoding, derive a horizontal component of the last position information, and derive a vertical component of the last position. A system for decoding and a displaying method are also provided.

We claim: 
     
       1. An apparatus for decoding last position information indicating a horizontal position and a vertical position of a last non-zero coefficient in a predetermined order within a current block to be decoded, the current block being included in a picture and including a plurality of coefficients, the apparatus comprising:
 one or more processors; 
 a communication unit; and 
 storage coupled to the one or more processors and the communication unit; 
 wherein the communication unit is configured to:
 transmit a request for a bitstream to an external system; and 
 receive the bitstream from the external system; and 
 
 wherein the one or more processors are configured to:
 obtain the bitstream including a first partial signal, a second partial signal, a third partial signal, and a fourth partial signal, in this predetermined order; 
 perform first arithmetic decoding on a first partial signal and a third second partial signal, respectively, to obtain a decoded first partial signal and a decoded third second partial signal, wherein in the first arithmetic decoding, decoding is performed on the third partial signal when the first partial signal indicates a greater value than a predetermined value; 
 perform second arithmetic decoding on a second third partial signal and a fourth partial signal, respectively, to obtain a decoded second third partial signal and a decoded fourth partial signal, the second arithmetic decoding being different from the first arithmetic decoding, wherein in the second arithmetic decoding, decoding is performed on the third partial signal when the first partial signal indicates a greater value than a predetermined value and decoding is performed on the fourth partial signal when the second partial signal indicates a greater value than the predetermined value; 
 derive a horizontal component of the last position information indicating the horizontal position of the non-zero coefficient from the decoded first partial signal and the decoded third partial signal; and 
 derive a vertical component of the last position information indicating the vertical position of the non-zero coefficient from the decoded second partial signal and the decoded fourth partial signal, 
 
 wherein when the current block to be decoded is a 4×4 block, the derived last position information only has a prefix part, and not a suffix part, and 
 wherein when the current block to be decoded is greater in size than a 4×4 block, the derived last position information for a first section of the current block corresponding to a 4×4 block only has a prefix part, and not a suffix part, whereas the derived last position information for a second section of the current block that does not correspond to a 4×4 block has a prefix part and a suffix part, a length of the suffix part is not determined by the size of block and varies depending on the value of the derived last position information. 
 
     
     
       2. A system for decoding last position information indicating a horizontal position and a vertical position of a last non-zero coefficient in a predetermined order within a current block to be decoded, the current block being included in a picture and including a plurality of coefficients, the system comprising:
 a first apparatus; 
 a second apparatus coupled to the first apparatus; and 
 a display coupled to the second apparatus; 
 wherein the first apparatus is configured to perform operations for transmitting a request for a bitstream to an external apparatus and letting the second apparatus receive the bitstream; 
 wherein the second apparatus includes:
 one or more processors; and 
 storage coupled to the one or more processors, the one or more processors being configured to perform operations for: 
 obtaining the bitstream including a first partial signal, a second partial signal, a third partial signal, and a fourth partial signal, in this predetermined order; 
 performing first arithmetic decoding on a first partial signal and a third second partial signal, respectively, to obtain a decoded first partial signal and a decoded third second partial signal, wherein in the first arithmetic decoding, decoding is performed on the third partial signal when the first partial signal indicates a greater value than a predetermined value; 
 performing second arithmetic decoding on a second third partial signal and a fourth partial signal, respectively, to obtain a decoded second third partial signal and a decoded fourth partial signal, the second arithmetic decoding being different from the first arithmetic decoding, wherein in the second arithmetic decoding, decoding is performed on the third partial signal when the first partial signal indicates a greater value than a predetermined value and decoding is performed on the fourth partial signal when the second partial signal indicates a greater value than the predetermined value; 
 deriving a horizontal component of the last position information indicating the horizontal position of the non-zero coefficient from the decoded first partial signal and the decoded third partial signal; 
 deriving a vertical component of the last position information indicating the vertical position of the non-zero coefficient from the decoded second partial signal and the decoded fourth partial signal; and 
 generating a reconstructed picture of the current block; 
 
 wherein the display is configured to display the reconstructed picture, 
 wherein when the current block to be decoded is a 4×4 block, the derived last position information only has a prefix part, and not a suffix part, and 
 wherein when the current block to be decoded is greater in size than a 4×4 block, the derived last position information for a first section of the current block corresponding to a 4×4 block only has a prefix part, and not a suffix part, whereas the derived last position information for a second section of the current block that does not correspond to a 4×4 block has a prefix part and a suffix part, a length of the suffix part is not determined by the size of block and varies depending on the value of the derived last position information. 
 
     
     
       3. A displaying method using a communication system, the displaying method comprising:
 transmitting a request for a bitstream including an encoded picture, the encoded picture being selectively encoded using one of 4×4 blocks and blocks greater in size than 4×4 blocks; 
 receiving the bitstream from an external apparatus through a network; 
 obtaining a bitstream including a first partial signal, a second partial signal, a third partial signal, and a fourth partial signal, in this predetermined order; 
 performing first arithmetic decoding, by one or more processors, on a first partial signal and a third second partial signal, respectively, to obtain a decoded first partial signal and a decoded third second partial signal, wherein in the first arithmetic decoding, decoding is performed on the third partial signal when the first partial signal indicates a greater value than a predetermined value; 
 performing second arithmetic decoding, by the one or more processors, on a second third partial signal and a fourth partial signal, respectively, to obtain a decoded second third partial signal and a decoded fourth partial signal, the second arithmetic decoding being different from the first arithmetic decoding, wherein in the second arithmetic decoding, decoding is performed on the third partial signal when the first partial signal indicates a greater value than a predetermined value and decoding is performed on the fourth partial signal when the second partial signal indicates a greater value than the predetermined value; 
 deriving a horizontal component of a last position information indicating a horizontal position of a non-zero coefficient which is last in a predetermined order, from the decoded first partial signal and the decoded third partial signal; 
 deriving a vertical component of a last position information indicating a vertical position of the non-zero coefficient, from the decoded second partial signal and the decoded fourth partial signal; 
 generating a reconstructed picture of the current block; and 
 displaying the reconstructed picture on a display, 
 wherein when the current block to be decoded is a 4×4 block, the derived last position information only has a prefix part, and not a suffix part, and 
 wherein when the current block to be decoded is greater in size than a 4×4 block, the derived last position information for a first section of the current block corresponding to a 4×4 block only has a prefix part, and not a suffix part, whereas the derived last position information for a second section of the current block that does not correspond to a 4×4 block has a prefix part and a suffix part, a length of the suffix part is not determined by the size of block and varies depending on the value of the derived last position information. 
 
     
     
       4. The apparatus for decoding last position information according to claim 1,
 wherein in the second arithmetic decoding, the number of bits of the decoded third partial signal and the number of bits of the decoded fourth partial signal are dependent on the value of the third partial signal and the fourth partial signal respectively.