Method and apparatus for adaptively encoding and decoding a quantization parameter based on a quadtree structure

A method for decoding a video by a decoding apparatus using derivation of a dequantization parameter, the method comprising:

• determining a parameter recorded unit for which dequantization parameter information is signaled, wherein the parameter recorded unit is split in a quadtree structure;
• determining a parameter prediction unit used for deriving a predicted dequantization parameter, wherein the parameter prediction unit comprises the parameter recorded unit;
• deriving the predicted dequantization parameter for the parameter prediction unit, wherein the predicted dequantization parameter is derived using an average value of dequantization parameters of a block neighboring to a left of the parameter prediction unit and a block neighboring above the parameter prediction unit;
• deriving a differential dequantization parameter for the parameter recorded unit based on the dequantization parameter information;
• deriving the dequantization parameter using a sum of the predicted dequantization parameter and the differential dequantization parameter;
• and
• performing dequantization using the dequantization parameter.