Coding device, decoding device, coding/decoding system, coding method, and decoding method

A coding/decoding system comprising:

• a coding device;
• a decoding device;
• and
• a storage device having a predetermined storage capacity, wherein
• the coding device comprises:
• predictive value data generator that sequentially generates predictive value data, which is a predictive value of pixel data;
• a predictive error data generator that sequentially generates predictive error data which is a difference between the pixel data and the predictive value data;
• a coder that sequentially codes the predictive error data to sequentially generate variable-length coded data, in which a code length is variable and equal to or shorter than a set maximum code length;
• and
• a coding controller that sequentially controls the coder, wherein,
• while a predetermined number of pieces of the variable-length coded data are generated, the coding controller sequentially calculates an accumulated value by accumulating a difference between the code length of the variable-length coded data generated by the coder and a target code length, and
• the coding controller sequentially sets the maximum code length based on the accumulated value and the number of coding times, which is the number of times of coding performed by the coder, such that the accumulated value is equal to or lower than 0 at the time the predetermined number of pieces of variable-length coded data are generated,
• the decoding device comprises:
• a decoder that decodes the variable-length coded data, which is generated by the coding device, by performing set decoding processing, and sequentially generates decoded predictive error data;
• a decoded predictive value data generator that sequentially generates decoded predictive value data, which is a predictive value of decoded pixel data;
• a decoded pixel data generator that sequentially generates the decoded pixel data, which is a sum of the decoded predictive error data and the decoded predictive value data;
• and
• a decoding controller that sequentially controls the decoder, wherein,
• while the predetermined number of pieces of the decoded pixel data are generated,
• the decoding controller sequentially calculates a decoding accumulated value by accumulating a difference between the code length of the variable-length coded data decoded by the decoder and the target code length used in the coding device,
• the decoding controller estimates coding processing, which is performed to the variable-length coded data to be decoded by the decoder, based on the decoding accumulated value and the number of decoding times, which is the number of times of decoding performed by the decoder, and
• the decoding controller sets the decoder such that decoding processing, which is an inverse processing of the estimated coding processing, is performed to the variable-length coded data,
• the variable-length coded data generated by the coding device is written in the storage device, and
• the decoding device generates the decoded pixel data using the variable-length coded data read from the storage device.

A coding method comprising:

• a predictive value data generating step of generating predictive value data, which is a predictive value of pixel data;
• a predictive error data generating step of generating predictive error data, which is a difference between the pixel data and the predictive value data generated in the predictive value data generating step;
• a coding step of coding the predictive error data, which is generated in the predictive error data generating step, to generate variable-length coded data, in which a code length is variable and equal to or shorter than a set maximum code length;
• an accumulated value calculating step of calculating an accumulated value by accumulating a difference between the code length of the variable-length coded data generated in the coding step and a target code length;
• and
• a maximum code length setting step of setting the maximum code length in the next coding step based on the accumulated value calculated in the accumulated value calculating step and the number of coding times, which is the number of times of the performed coding step, wherein
• the predictive value data generating step, the predictive error data generating step, the coding step, the accumulated value calculating step, and the maximum code length setting step are repeatedly performed until a predetermined number of pieces of the variable-length coded data are generated, and
• the maximum code length is set in the maximum code length setting step such that the accumulated value is equal to or lower than 0 at the time the predetermined number of pieces of variable-length coded data are generated.