Image decoding method and device using residual information in image coding system

An encoding apparatus for image encoding, the encoding apparatus comprising:

• a memory;
• and
• at least one processor connected to the memory, the at least one processor configured to:
• generate intra prediction mode information for a current block;
• derive a residual sample for the current block;
• derive a transform coefficient based on the residual sample for the current block;
• derive a maximum number of context-coded bins for context syntax elements for the transform coefficient;
• entropy encode the context syntax elements based on the maximum number;
• and
• output a bitstream including the intra prediction mode information and residual information for the current block including the entropy encoded context syntax elements,
• wherein the context syntax elements include:
• a significant coefficient flag representing whether the transform coefficient is a non-zero transform coefficient,
• a parity level flag for parity of a transform coefficient level for the transform coefficient,
• a first transform coefficient level flag regarding whether the transform coefficient level is greater than a first threshold, and
• a second transform coefficient level flag regarding whether the transform coefficient level of a quantized transform coefficient is greater than a second threshold, and
• wherein the maximum number is a maximum number for a sum of following numbers:
• a number of context-coded bins of significant coefficient flags,
• a number of context-coded bins of first transform coefficient level flags,
• a number of context-coded bins of parity level flags, and
• a number of context-coded bins of second transform coefficient level flags.

An apparatus for transmitting data for an image, the apparatus comprising:

• at least one processor configured to obtain a bitstream of image information comprising intra prediction mode information and residual information for a current block including context syntax elements;
• and
• a transmitter configured to transmit the data including the bitstream of the image information comprising the intra prediction mode information and the residual information,
• wherein the context syntax elements are entropy encoded based on a maximum number of context-coded bins for the context syntax elements,
• wherein the context syntax elements include:
• a significant coefficient flag representing whether a transform coefficient for the current block is a non-zero transform coefficient,
• a parity level flag for parity of a transform coefficient level for the transform coefficient,
• a first transform coefficient level flag regarding whether the transform coefficient level is greater than a first threshold, and
• a second transform coefficient level flag regarding whether the transform coefficient level of a quantized transform coefficient is greater than a second threshold, and
• wherein the maximum number is a maximum number for a sum of following numbers:
• a number of context-coded bins of significant coefficient flags,
• a number of context-coded bins of first transform coefficient level flags,
• a number of context-coded bins of parity level flags, and
• a number of context-coded bins of second transform coefficient level flags.