Coding of information about transform kernel set

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

• deriving residual samples for a current block;
• deriving transform coefficients for the current block by performing a transform on the residual samples based on a transform kernel set;
• deriving quantized transform coefficients by performing a quantization on the transform coefficients;
• generating multiple transform selection (MTS) index related to the transform kernel set and residual information related to the quantized transform coefficients;
• and
• encoding image information including the MTS index and the residual information to output a bitstream,
• wherein the MTS index represents the transform kernel set to be applied to the current block among transform kernel set candidates,
• wherein the transform kernel set comprises a transform kernel to be applied to the current block in a horizontal direction and a transform kernel to be applied to the current block in a vertical direction,
• wherein bins of a bin string of the MTS index are represented based on context coding, the context coding being performed based on values of context index increment for the bins of the bin string of the MTS index,
• wherein the bins of the bin string of the MTS index include first, second, third, and fourth bins, and
• wherein a value of the context index increment for the first bin is fixed to 0, a value of the context index increment for the second bin is fixed to 1, a value of the context index increment for the third bin is fixed to 2, and a value of the context index increment for the fourth bin is fixed to 3.

A transmission method of data for an image, the method comprising:

• obtaining a bitstream for the image, the bitstream is generated based on deriving residual samples for a current block, deriving transform coefficients for the current block by performing a transform on the residual samples based on a transform kernel set, deriving quantized transform coefficients by performing a quantization on the transform coefficients, generating multiple transform selection (MTS) index related to the transform kernel set and residual information related to the quantized transform coefficients, and encoding image information including the MTS index and the residual information to output a bitstream;
• transmit the data comprising the bitstream for the image,
• wherein the MTS index represents the transform kernel set to be applied to the current block among transform kernel set candidates,
• wherein the transform kernel set comprises a transform kernel to be applied to the current block in a horizontal direction and a transform kernel to be applied to the current block in a vertical direction,
• wherein bins of a bin string of the MTS index are represented based on context coding, the context coding being performed based on values of context index increment for the bins of the bin string of the MTS index,
• wherein the bins of the bin string of the MTS index include first, second, third, and fourth bins, and
• wherein a value of the context index increment for the first bin is fixed to 0, a value of the context index increment for the second bin is fixed to 1, a value of the context index increment for the third bin is fixed to 2, and a value of the context index increment for the fourth bin is fixed to 3.