Transform-based image coding method and device therefor

An image encoding apparatus, comprising:

• a memory;
• and
• at least one processor connected to the memory, the at least one processor configured to:
• derive residual samples for a current block having a first width and a first height,
• derive quantized transform coefficients based on the residual samples for the current block, and
• encode residual information comprising information on the quantized transform coefficients,
• wherein the residual information comprises last significant coefficient position information,
• wherein for encoding the residual information, the at least one processor is further configured to:
• derive a zero-out block for the current block, wherein the zero-out block has a second width and a second height,
• derive a last significant coefficient position within the current block, and
• encode the last significant coefficient position information indicating the last significant coefficient position,
• wherein the last significant coefficient position information comprises last significant coefficient prefix information,
• wherein the last significant coefficient prefix information comprises x-axis prefix information and y-axis prefix information,
• wherein a value of the x-axis prefix information is encoded, based on a context increment of the x-axis prefix information, to be less than or equal to a first maximum value, the context increment of the x-axis prefix information being derived based on the first width of the current block, the first maximum value being set based on the second width of the zero-out block,
• wherein a value of the y-axis prefix information is encoded, based on a context increment of the y-axis prefix information, to be less than or equal to a second maximum value, the context increment of the y-axis prefix information being derived based on the first height of the current block, the second maximum value being set based on the second height of the zero-out block, and
• wherein the second width and the second height of the zero-out block are less than the first width and the first height of the current block, respectively.

A transmission apparatus of data for an image, comprising:

• at least one processor configured to obtain a bitstream for the image, wherein the bitstream is generated based on deriving residual samples for a current block having a first width and a first height, deriving quantized transform coefficients based on the residual samples for the current block, and encoding residual information comprising information on the quantized transform coefficients;
• and
• a transmitter configured to transmit the data including the bitstream,
• wherein the residual information comprises last significant coefficient position information,
• wherein encoding the residual information comprises:
• deriving a zero-out block for the current block, wherein the zero-out block has a second width and a second height;
• deriving a last significant coefficient position within the current block;
• and
• encoding the last significant coefficient position information indicating the last significant coefficient position,
• wherein the last significant coefficient position information comprises last significant coefficient prefix information,
• wherein the last significant coefficient prefix information comprises x-axis prefix information and y-axis prefix information,
• wherein a value of the x-axis prefix information is encoded, based on a context increment of the x-axis prefix information, to be less than or equal to a first maximum value, the context increment of the x-axis prefix information being derived based on the first width of the current block, the first maximum value being set based on the second width of the zero-out block,
• wherein a value of the y-axis prefix information is encoded, based on a context increment of the y-axis prefix information, to be less than or equal to a second maximum value, the context increment of the y-axis prefix information being derived based on the first height of the current block, the second maximum value being set based on the second height of the zero-out block, and
• wherein the second width and the second height of the zero-out block are less than the first width and the first height of the current block, respectively.