Method and apparatus for configuring transform for video compression

An encoding apparatus for image encoding, the encoding apparatus comprising:

• a memory;
• and
• at least one processor connected to the memory, the at least one processor configured to:
• determine a prediction mode as an inter prediction mode to be used for a block;
• derive a transform combination being applied to a transform unit, wherein the transform combination is configured with a horizontal transform and a vertical transform and includes one of (DST-7, DST-7), (DST-7, DCT-8), (DCT-8, DST-7) and (DCT-8, DCT-8);
• perform a transform on the transform unit based on the transform combination;
• determine one transform configuration group of a plurality of transform configuration groups to be used for the block of the inter prediction mode, wherein the plurality of transform configuration groups include a plurality of transform combinations;
• generate a transform index corresponding to the transform combination,
• wherein the transform index (i) indicates one transform combination of the plurality of transform configuration groups, (ii) is a single transform index corresponding to a first index value for a horizontal transform and a second index value for a vertical transform, and (iii) is comprised of values of 0, 1, 2, 3, 4, and
• wherein the first index value and the second index value are determined based on the transform index and the one transform configuration group.

An apparatus for transmitting data for an image, the apparatus comprising:

• at least one processor configured to obtain a bitstream generated by an image encoding method;
• and
• a transmitter configured to transmit the bitstream,
• wherein the image encoding method comprises:
• determining a prediction mode as an inter prediction mode to be used for a block;
• deriving a transform combination being applied to a transform unit, wherein the transform combination is configured with a horizontal transform and a vertical transform and includes one of (DST-7, DST-7), (DST-7, DCT-8), (DCT-8, DST-7) and (DCT-8, DCT-8);
• performing a transform on the transform unit based on the transform combination;
• determining one transform configuration group of a plurality of transform configuration groups to be used for the block of the inter prediction mode, wherein the plurality of transform configuration groups include a plurality of transform combinations;
• generating a transform index corresponding to the transform combination,
• wherein the transform index (i) indicates one transform combination of the plurality of transform configuration groups, (ii) is a single transform index corresponding to a first index value for a horizontal transform and a second index value for a vertical transform, and (iii) is comprised of values of 0, 1, 2, 3, 4, and
• wherein the first index value and the second index value are determined based on the transform index and the one transform configuration group.