Encoding method and apparatus therefor, and decoding method and apparatus therefor

An image decoding apparatus comprising:

• at least one processor configured to:
• split an upper coding block into a plurality of lower coding blocks according to split information;
• determine a current quantization group based on a split value of a current coding block among the plurality of lower coding blocks and a split value of the current quantization group;
• obtain a quantization parameter of the current quantization group based on a predicted quantization parameter and a difference quantization parameter;
• and
• inverse-quantize transform coefficients in a current transform block in the current coding block using the quantization parameter,
• wherein the predicted quantization parameter is obtained using at least one of a quantization parameter of an upper adjacent block of the current quantization group and a quantization parameter of a left adjacent block of the current quantization group, and
• wherein:
• the split value of the current coding block is increased by 1 if the current coding block is obtained by splitting the upper coding block into two lower coding blocks according to non-quadtree split, and
• the split value of the current coding block is increased by 2 if the current coding block is obtained by splitting the upper coding block into four lower coding blocks according to quadtree split.

An image encoding method comprising:

• splitting an upper coding block into a plurality of lower coding blocks;
• determining a current quantization group based on a split value of a current coding block among the plurality of lower coding blocks and a split value of the current quantization group;
• obtaining a quantization parameter of the current quantization group;
• and
• quantizing transform coefficients in a current transform block in the current coding block using the quantization parameter,
• wherein a difference quantization parameter is obtained based on the quantization parameter of the current quantization group and a predicted quantization parameter,
• wherein the predicted quantization parameter is obtained using at least one of a quantization parameter of an upper adjacent block of the current quantization group and a quantization parameter of a left adjacent block of the current quantization group, and
• wherein:
• the split value of the current coding block is increased by 1 if the current coding block is obtained by splitting the upper coding block into two lower coding blocks according to non-quadtree split, and
• the split value of the current coding block is increased by 2 if the current coding block is obtained by splitting the upper coding block into four lower coding blocks according to quadtree split.