Method for determining color difference component quantization parameter and device using the method
Disclosed are a method for determining a color difference component quantization parameter and a device using the method. Method for decoding an image can comprise the steps of: decoding a color difference component quantization parameter offset on the basis of size information of a transform unit; and calculating a color difference component quantization parameter index on the basis of the decoded color difference component quantization parameter offset. Therefore, the present invention enables effective quantization by applying different color difference component quantization parameters according to the size of the transform unit when executing the quantization.
1. 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,
wherein the inverse-quantizer comprises:
a chrominance component quantization parameter index calculator configured to calculate a chrominance component quantization parameter index by using a luminance component quantization parameter, 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.
2. The video decoding apparatus of claim 1 , wherein the quantization group includes the transform blocks with different sizes.
3. The video decoding apparatus of claim 1 , wherein the pre-defined mapping table defines a mapping relationship between the chrominance component quantization parameter and the chrominance component quantization parameter index.
4. A video encoding apparatus comprising:
a 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 determine the chrominance component quantization parameter to be applied to the determined quantization group, and configured to quantize transform coefficients of a transform block included in the determined quantization group by using the determined chrominance component quantization parameter; and
an encoder configured to encode the chrominance component quantization parameter,
wherein the encoder comprises:
a chrominance component quantization parameter index calculator configured to calculate a chrominance component quantization parameter index based on a pre-defined mapping table and the chrominance component quantization parameter; and
a chrominance component quantization parameter index encoder configured to encode the chrominance component quantization parameter index by using a luminance component quantization parameter, 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 included in a picture parameter set of a bitstream, and the second chrominance component quantization parameter offset is included in a slice header of the bitstream.
5. The video encoding apparatus of claim 4 , wherein the quantization group includes the transform blocks with different sizes.
6. The video encoding apparatus of claim 4 , wherein the pre-defined mapping table defines a mapping relationship between the chrominance component quantization parameter and the chrominance component quantization parameter index.
7. A non-transitory computer-readable storage medium storing a bitstream that is generated by a video encoding apparatus, wherein the video encoding apparatus comprises
a 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 determine the chrominance component quantization parameter to be applied to the determined quantization group, and configured to quantize transform coefficients of a transform block included in the determined quantization group by using the determined chrominance component quantization parameter; and
an encoder configured to encode the chrominance component quantization parameter,
wherein the encoder comprises:
a chrominance component quantization parameter index calculator configured to calculate a chrominance component quantization parameter index based on a pre-defined mapping table and the chrominance component quantization parameter; and
a chrominance component quantization parameter index encoder configured to encode the chrominance component quantization parameter index by using a luminance component quantization parameter, 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 included in a picture parameter set of a bitstream, and the second chrominance component quantization parameter offset is included in a slice header of the bitstream.
8. The non-transitory computer-readable storage medium of claim 7 , wherein the quantization group includes the transform blocks with different sizes.
9. The non-transitory computer-readable storage medium of claim 7 , wherein the pre-defined mapping table defines a mapping relationship between the chrominance component quantization parameter and the chrominance component quantization parameter index.
10. A non-transitory computer-readable recording medium storing a bitstream which is received and decoded by a video decoding apparatus and used to reconstruct a video,
wherein the bitstream comprises 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 the bitstream, and the second chrominance component quantization parameter offset is extracted from a slice header of the bitstream,
a first chrominance component quantization parameter offset of a picture level and a second chrominance component quantization parameter offset of a slice level are used with a luminance component quantization parameter to calculate a chrominance component quantization parameter index,
the chrominance component quantization parameter index is used with a pre-defined mapping table to calculate a chrominance component quantization parameter,
the chrominance component quantization parameter is applied to a quantization group and used to inverse-quantize transform coefficients of a transform block included in the quantization group, and
wherein the quantization group is a group of a plurality of transform blocks to which the same chrominance component quantization parameter is applied, a size of the quantization group being determined by the video decoding apparatus.