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 order; 
 perform first arithmetic decoding on a first partial signal and a third partial signal, respectively, to obtain a decoded first partial signal and a decoded third 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 partial signal and a fourth partial signal, respectively, to obtain a decoded second 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 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. 
   
     
     
       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 order; 
 performing first arithmetic decoding on a first partial signal and a third partial signal, respectively, to obtain a decoded first partial signal and a decoded third 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 partial signal and a fourth partial signal, respectively, to obtain a decoded second 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 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.   
     
     
       3. A displaying method using a communication system, the displaying method comprising:
 transmitting a request for a bitstream including an encoded picture;   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 order;   performing first arithmetic decoding on a first partial signal and a third partial signal, respectively, to obtain a decoded first partial signal and a decoded third 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 partial signal and a fourth partial signal, respectively, to obtain a decoded second 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 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.   
     
     
       4. A method for transmitting a bitstream via a network, the method comprising:
 transmitting the bitstream via the network,   wherein the bitstream comprises 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 encoded, the current block being included in a picture and including a plurality of coefficients,   wherein the bitstream is generated by performing operations, including
 binarizing a horizonal component of the last position information and a vertical component of the last position information into a first binary signal and a second binary signal, respectively, the vertical component indicating a vertical position of the last non-zero coefficient, and the horizontal component indicating a horizontal position of the last non-zero coefficient; 
 encoding a first partial signal and a second partial signal, respectively, into an encoded first partial signal and an encoded second partial signal, by first arithmetic coding, and encoding a third partial signal and a fourth partial signal, respectively, into an encoded third partial signal and an encoded fourth partial signal, by second arithmetic coding different from the first arithmetic coding, the first partial signal being a part of the first binary signal, the second partial signal being a part of the second binary signal, the third partial signal being another part of the first binary signal, and the fourth partial signal being another part of the second binary signal; and 
 arranging the encoded first partial signal, the encoded second partial signal, the encoded third partial signal, and the encoded fourth partial signal in the bit stream, in this order, 
   wherein when the current block to be encoded is a 4×4 block, the binarized last position information only has a prefix part, and not a suffix part, and   wherein when the current block to be encoded is greater in size than a 4×4 block, the binarized 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 binarized 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 binarized last position information.