Method for determining color difference component quantization parameter and device using the method

A video decoding apparatus comprising:

• an inverse-quantizer configured to determine a size of a quantization group, the quantization group being a group of a plurality of transform blocks to which a same chrominance component quantization parameter is applied, configured to calculate the chrominance component quantization parameter to be applied to the determined quantization group, and configured to inverse-quantize transform coefficients of a transform block included in the determined quantization group by using the calculated chrominance component quantization parameter;
• and
• an inverse-transformer configured to generate a residual block by inverse-transforming the inverse-quantized transform coefficients,
• wherein the inverse-quantizer comprises:
• a chrominance component quantization parameter index calculator configured to calculate a chrominance component quantization parameter index by using a first chrominance component quantization parameter offset of a picture level and a second chrominance component quantization parameter offset of a slice level, wherein the first chrominance component quantization parameter offset is extracted from a picture parameter set of a bitstream, and the second chrominance component quantization parameter offset is extracted from a slice header of the bitstream;
• and
• a chrominance component quantization parameter calculator configured to calculate the chrominance component quantization parameter based on a pre-defined mapping table and the chrominance component quantization parameter index.