Image encoding/decoding method and apparatus performing residual processing by using adaptive color space transformation, and method for transmitting bitstream

An image decoding method performed by an image decoding apparatus, the method comprising:

• determining a current block based on partitioning an image;
• determining a color space transformation being available for residual samples of the current block;
• determining to apply the color space transformation for the residual samples of the current block based on the color space transformation being available;
• determining quantization parameter of the current block based on the color space transformation being applied;
• and
• determining transformation coefficient of the current block based on the quantization parameter,
• wherein information for the color space transformation being available and information for the color space transformation being applied are respectively decoded from a bitstream,
• wherein the quantization parameter is derived by calculation using initial quantization parameter and quantization parameter offset, based on a color component of the current block,
• wherein the quantization parameter offset is derived based on the color component of the current block and the color space transformation for the residual samples of the current block,
• wherein a lower limit value of the quantization parameter is set based on transform skip flag of the current block, and
• wherein the transform skip flag is obtained based on the color component of the current block.