Intra prediction method and device

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

• performing a primary transform on a current block;
• determining whether a secondary transform is applied to the primary-transformed current block;
• performing the secondary transform on the primary-transformed current block in response to that the secondary transform is determined to be applied to the current block;
• and
• encoding the secondary-transformed current block,
• wherein, the primary transform is a separable 2-D transform and the secondary transform is a non-separable 2-D transform.

A non-transitory computer-readable recording medium storing a bitstream which is generated by an image encoding method comprising:

• performing a primary transform on a current block;
• determining whether a secondary transform is applied to the primary-transformed current block;
• performing the secondary transform on the primary-transformed current block in response to that the secondary transform is determined to be applied to the current block;
• and
• encoding the secondary-transformed current block,
• wherein, the primary transform is a separable 2-D transform and the secondary transform is a non-separable 2-D transform.