Image coding method and device using transform skip flag

An apparatus for image encoding, the apparatus comprising:

• memory storing instructions that, when executed, cause one or more processors to perform operations comprising:
• deriving prediction samples by performing prediction on a current block,
• deriving residual samples for the current block, generating prediction mode information related to the prediction on the current block,
• generating residual related information related to the residual samples for the current block, and
• encoding image information comprising the prediction mode information and the residual related information,
• wherein the prediction mode information is related to whether inter prediction or intra prediction is applied to the current block,
• wherein the residual related information comprises a transform skip flag based on a size of the current block and a maximum transform skip size,
• wherein the transform skip flag is related to whether a transform skip is applied to the current block,
• wherein the image information comprises information about the maximum transform skip size,
• wherein the information about the maximum transform skip size comprises a log 2_transform_skip_max_size_minus2 syntax element, and
• wherein the maximum transform skip size is represented based on the following equation,
• MaxTsSize
• =
• 1
• ⁢
• <<
• (log
• ⁢
• ⁢
• 2
• ⁢
• _transform
• ⁢
• _skip
• ⁢
• _max
• ⁢
• _size
• ⁢
• _minus2
• +
• 2
• )
• ,
• where the MaxTsSize represents the maximum transform skip size, and the log 2_transform_skip_max_size_minus2 represents a value of the log 2_transform_skip_max_size_minus2 syntax element.

An apparatus for transmitting image data, the apparatus comprising:

• memory storing instructions that, when executed, cause one or more processors to perform operations comprising:
• generating a bitstream, wherein the bitstream is generated by:
• deriving prediction samples by performing prediction on a current block,
• deriving residual samples for the current block,
• generating prediction mode information related to the prediction on the current block,
• generating residual related information related to the residual samples for the current block, and
• generating the bitstream by encoding image information comprising the prediction mode information and the residual related information, and transmitting the image data comprising the bitstream,
• wherein the prediction mode information is related to whether inter prediction or intra prediction is applied to the current block,
• wherein the residual related information comprises a transform skip flag based on a size of the current block and a maximum transform skip size,
• wherein the transform skip flag is related to whether a transform skip is applied to the current block,
• wherein the image information comprises information about the maximum transform skip size,
• wherein the information about the maximum transform skip size comprises a log 2_transform_skip_max_size_minus2 syntax element, and
• wherein the maximum transform skip size is represented based on the following equation,
• MaxTsSize
• =
• 1
• ⁢
• <<
• (log
• ⁢
• ⁢
• 2
• ⁢
• _transform
• ⁢
• _skip
• ⁢
• _max
• ⁢
• _size
• ⁢
• _minus2
• +
• 2
• )
• ,
• where the MaxTsSize represents the maximum transform skip size, and the log 2_transform_skip_max_size_minus2 represents a value of the log 2_transform_skip_max_size_minus2 syntax element.