Context coding for information on transform kernel set in image coding system

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

• deriving prediction samples by performing prediction on a current block, and generating prediction mode information based on the prediction samples;
• generating residual samples for the current block based on the prediction samples;
• deriving transform coefficients for the current block based on the residual samples, and generating information about a transform kernel set and residual information based on the transform coefficients;
• and
• encoding image information including the prediction mode information, the information about the transform kernel set and the residual information,
• wherein the information about the transform kernel set indicate the transform kernel set applied to the current block from among transform kernel set candidates,
• wherein at least one bin among bins of a bin string for the information about the transform kernel set is represented based on context coding,
• wherein the context coding is performed based on at least one context model,
• wherein a number of context models for the context coding of a first bin among the bins of the bin string is one, wherein the context model for the context coding of the first bin is represented based on a value of a context index increment for the first bin.

A non-transitory computer-readable digital storage medium storing a bitstream generated by an image encoding method, the method comprising:

• deriving prediction samples by performing prediction on a current block, and generating prediction mode information based on the prediction samples;
• generating residual samples for the current block based on the prediction samples;
• deriving transform coefficients for the current block based on the residual samples, and generating information about a transform kernel set and residual information based on the transform coefficients;
• and
• encoding image information to generate the bitstream, wherein the image information includes the prediction mode information, the information about the transform kernel set and the residual information,
• wherein the information about the transform kernel set indicate the transform kernel set applied to the current block from among transform kernel set candidates,
• wherein at least one bin among bins of a bin string for the information about the transform kernel set is represented based on context coding,
• wherein the context coding is performed based on at least one context model,
• wherein a number of context models for the context coding of a first bin among the bins of the bin string is one, wherein the context model for the context coding of the first bin is represented based on a value of a context index increment for the first bin.