Lookup table based decoder side intra mode derivation

An apparatus comprising:

• at least one processor;
• and
• at least one memory storing instructions that, when executed by the at least one processor, causes the apparatus at least to:
• determine a horizontal direction strength value using at least one neighboring sample of a current block of at least one picture;
• determine a vertical direction strength value using the at least one neighboring sample of the current block of the at least one picture;
• determine a ratio value in a logarithmic domain, based on the horizontal direction strength value and the vertical direction strength value;
• determine an angle index that is mapped to the ratio value using a lookup table;
• determine an intra prediction mode of the at least one neighboring sample, based on the angle index;
• and
• generate a prediction block for the current block, based on the intra prediction mode.

A method comprising:

• determining a horizontal direction strength value using at least one neighboring sample of a current block of at least one picture;
• determining a vertical direction strength value using the at least one neighboring sample of the current block of the at least one picture;
• determining a ratio value in a logarithmic domain, based on the horizontal direction strength value and the vertical direction strength value;
• determining, using a lookup table, an angle index that is mapped to the ratio value;
• determining an intra prediction mode of the at least one neighboring sample, based on the angle index;
• and
• decoding the current block based on the intra prediction mode.

A method comprising:

• determining a horizontal direction strength value using at least one neighboring sample of a current block of at least one picture;
• determining a vertical direction strength value using the at least one neighboring sample of the current block of the at least one picture;
• determining a ratio value in a logarithmic domain, based on the horizontal direction strength value and the vertical direction strength value;
• determining an angle index that is mapped to the ratio value using a lookup table;
• determining an intra prediction mode of the at least one neighboring sample, based on the angle index;
• and
• generating a prediction block for the current block, based on the intra prediction mode.