determining whether to divide a first depth coding block into three second depth coding blocks or not;

in response to a determination of dividing the first depth coding block, dividing the first depth coding block into the three second depth coding blocks in a vertical direction or a horizontal direction,

wherein one of the three second depth coding blocks has ½ size of the first depth coding block and each of the others of the three second depth coding blocks has ¼ size of the first depth coding block;

determining whether to divide a second depth coding block into two third depth coding blocks or not;

in response to a determination of dividing the second depth coding block, dividing the second depth coding block into the two third depth coding blocks in the vertical direction or the horizontal direction;

obtaining prediction samples for a current block, the current block being one of the third depth coding blocks or one of sub-blocks generated by dividing one of the third depth coding blocks;

obtaining residual samples for the current block; and

reconstructing the current block by summing the prediction samples and the residual samples,

wherein whether it is allowed to divide the second depth coding block in the vertical direction or whether it is allowed to divide the second depth coding block in the horizontal direction is determined based on an index of the second depth coding block,

wherein, for the second depth coding block that has ½ size of the first depth coding block, dividing the second depth coding block in a same direction as the first depth coding block is not allowed,

wherein the residual samples for the current block are obtained by performing an inverse-transform or skipping the inverse transform, and

wherein in response to the current block being one of two sub-blocks generated by partitioning the third depth coding blocks in the horizontal direction or the vertical direction, it is not allowed to skip the inverse-transform for the current block regardless of a size of the current block, and decoding a flag, indicating whether the inverse-transform is skipped or not, is omitted.