Method and apparatus for video coding

A method for video decoding in a decoder, comprising:

• decoding coding information of a coefficient block from a coded video bitstream, the coding information indicating a size of the coefficient block;
• determining, based on the size of the coefficient block, whether to reduce a number of calculations in one of inverse horizontal and inverse vertical transforms of an inverse primary transform, the inverse vertical transform transforming transform coefficients of the coefficient block to intermediate data of an intermediate block, and the inverse horizontal transform transforming the intermediate data to residual data in a residual block;
• performing the inverse primary transform, wherein:
• when the number of calculations in the inverse vertical transform is determined to be reduced, top 16 rows of the intermediate data in the intermediate block are calculated by the inverse vertical transform and the remaining intermediate data in the intermediate block are zero;
• and
• when the number of calculations in the inverse horizontal transform is determined to be reduced, left 16 columns of the residual data in the residual block are calculated by the inverse horizontal transform and the remaining residual data in the residual block are zero;
• and
• reconstructing a sample in the residual block based on the residual data.

An apparatus for video decoding, comprising processing circuitry configured to:

• decode coding information of a coefficient block from a coded video bitstream, the coding information indicating a size of the coefficient block;
• determine, based on the size of the coefficient block, an order in which inverse horizontal and inverse vertical transforms of an inverse primary transform are to be performed on transform coefficients of the coefficient block to obtain residual data of a residual block, wherein
• when the size of the coefficient block satisfies a condition, perform the inverse vertical transform after the inverse horizontal transform is performed on the transform coefficients of the coefficient block;
• and
• reconstruct a sample in the residual block based on the residual data.

An apparatus for video decoding, comprising processing circuitry configured to:

• decode coding information of a coefficient block from a coded video bitstream, the coding information indicating a size of the coefficient block;
• determine, based on the size of the coefficient block, whether to reduce a number of calculations in one of inverse horizontal and inverse vertical transforms of an inverse primary transform, the inverse vertical transform transforming transform coefficients of the coefficient block to intermediate data of an intermediate block, and the inverse horizontal transform transforming the intermediate data to residual data in a residual block;
• perform the inverse primary transform, wherein:
• when the number of calculations in the inverse vertical transform is determined to be reduced, top 16 rows of the intermediate data in the intermediate block are calculated by the inverse vertical transform and the remaining intermediate data in the intermediate block are zero;
• and
• when the number of calculations in the inverse horizontal transform is determined to be reduced, left 16 columns of the residual data in the residual block are calculated by the inverse horizontal transform and the remaining residual data in the residual block are zero;
• and
• reconstruct a sample in the residual block based on the residual data.