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

Abstract

An image coding method for performing compression-coding on image data includes: binarizing a signal to be coded of the image data, to generate a binary signal; determining a low-order context which is a context associated with a type of the signal to be coded, and a high-order context that is common to the low-order context and a context associated with another type; calculating coding probability information to be used in arithmetic coding of the binary signal, using (i) high-order probability information corresponding to the determined high-order context and (ii) low-order probability information corresponding to the determined low-order context; performing the arithmetic coding on the binary signal using the coding probability information; and updating the high-order probability information and the low-order probability information based on the binary signal.

The invention claimed:  
     
       1. An image coding method for performing compression-coding on pixel image data, said image coding method comprising:
 binarizing a signal to be coded of the pixel image data, to generate a binary signal; 
 determining a first low-order context, wherein the first low-order context is associated with a type of the signal to be coded; 
 determining a first high-order context that is common to the first low-order context and at least one second low-order context which is other than the first low-order context, wherein the second low-order context is associated with another type of a signal; 
 calculating coding probability information to be used in arithmetic coding of the binary signal, using first high-order probability information corresponding to the determined first high-order context and first low-order probability information corresponding to the determined first low-order context; 
 performing the arithmetic coding on the binary signal using the calculated coding probability information; and 
 updating the first high-order probability information and the first low-order probability information based on the binary signal. 
 
     
     
       2. The image coding method according to  claim 1 , further comprising obtaining type information indicating the type of the signal to be coded,
 wherein in said determining, the first high-order probability information and the first low-order probability information are determined by referring, based on the type information, to a table in which the following are associated with one another: a plurality of types; a high-order context common to the types; and low-order contexts each associated with a corresponding one of the types. 
 
     
     
       3. The image coding method according to  claim 1 , wherein in said calculating, the coding probability information is calculated by weighted-summation of the first high-order probability information and the first low-order probability information. 
     
     
       4. The image coding method according to  claim 1 , further comprising obtaining a control signal to be used in the calculation of the coding probability information,
 wherein in said calculating, the coding probability information is calculated using the first high-order probability information, the first low-order probability information, and the control signal. 
 
     
     
       5. The image coding method according to  claim 4 , further comprising coding the control signal. 
     
     
       6. The image coding method according to  claim 1 , wherein the first high-order probability information and the first low-order probability information is an index indicating a value of a symbol occurrence probability. 
     
     
       7. The image coding method according to  claim 1 , wherein the first high-order probability information and the first low-order probability information is a value of a symbol occurrence probability. 
     
     
       8. An image coding apparatus that performs compression-coding on pixel image data, said image coding apparatus comprising:
 a hardware processor; and 
 a non-transitory memory storing thereon a program which is executed by the hardware processor and causes the image coding apparatus to: 
 binarize a signal to be coded of the pixel image data, to generate a binary signal; 
 determine a first low-order context, wherein the first low-order context is associated with a type of the signal to be coded; 
 determine a first high-order context that is common to the first low-order context and at least one second low-order context which is other than the first low-order context, wherein the second low-order context is associated with another type of a signal associated with another type; 
 calculate coding probability information to be used in arithmetic coding of the binary signal, using first high-order probability information corresponding to the determined first high-order context and first low-order probability information corresponding to the determined first low-order context; 
 perform the arithmetic coding on the binary signal using the calculated coding probability information; and 
 update the first high-order probability information and the first low-order probability information based on the binary signal. 
 
     
     
       9. The image coding apparatus according to  claim 8 , wherein said image coding apparatus is configured as an integrated circuit. 
     
     
       10. A non-transitory computer-readable recording medium on which a program is stored, the program causing a computer to execute the image coding method according to  claim 1 .