Method and apparatus for quantization
Disclosed herein are a video decoding method and apparatus and a video encoding method and apparatus. In quantization and dequantization, multiple quantization methods and multiple dequantization methods may be used. The multiple quantization methods include a variable-rate step quantization method and a fixed-rate step quantization method. The variable-rate step quantization method may be a quantization method in which an increment in a quantization step depending on an increase in a value of a quantization parameter by 1 is not fixed. The fixed-rate step quantization method may be a quantization method in which the increment in the quantization step depending on the increase of the value of the quantization parameter by 1 is fixed.
1. An encoding method, comprising:
performing quantization that uses a quantization method selected from multiple quantization methods, to generate a quantization parameter difference value,
wherein the selected quantization method is a variable-rate step quantization method,
wherein the variable-rate step quantization method is a quantization method in which an increment in a quantization step depending on an increase in a value of a quantization parameter by 1 is not fixed,
wherein the quantization parameter difference value is a difference between a median value and the value of the quantization parameter or a difference between a value of a quantization parameter in an upper unit and a value of a quantization parameter in a lower unit to be used for the quantization for the lower unit, and
wherein the median value is an intermediate value falling within a range of the quantization parameter of the variable-rate step dequantization method.
2. The encoding method of claim 1 , wherein, as the value of the quantization parameter is smaller, the increment in the quantization step of the variable-rate step quantization method depending on the increase in the value of the quantization parameter by 1 is larger.
3. The encoding method of claim 1 ,
wherein the multiple quantization methods comprise a fixed-rate step quantization method and the variable-rate step quantization method, and
wherein the fixed-rate step quantization method is a quantization method in which the increment in the quantization step depending on the increase in the value of the quantization parameter by 1 is fixed.
4. The encoding method of claim 3 , wherein the increment in the quantization step of the variable-rate step quantization method is less than the increment in the quantization step of the fixed-rate step quantization method in a region in which the value of the quantization parameter is relatively large.
5. A decoding method, comprising:
acquiring a quantization parameter using a quantization parameter difference value; and
performing dequantization that uses a dequantization method selected from multiple quantization methods,
wherein the selected dequantization method is a variable-rate step dequantization method, and
wherein the variable-rate step dequantization method is a dequantization method in which an increment in a quantization step depending on an increase in a value of the quantization parameter by 1 is not fixed,
wherein the quantization parameter is used for the dequantization,
wherein the quantization parameter difference value is a difference between a median value and the value of the quantization parameter or a difference between a value of a quantization parameter in an upper unit and a value of a quantization parameter in a lower unit to be used for the dequantization for the lower unit, and
wherein the median value is an intermediate value falling within a range of the quantization parameter of the variable-rate step dequantization method.
6. The decoding method of claim 5 , wherein, as the value of the quantization parameter is smaller, the increment in the quantization step of the variable-rate step dequantization method depending on the increase in the value of the quantization parameter by 1 is larger.
7. The decoding method of claim 5 ,
wherein the multiple dequantization methods comprise a fixed-rate step dequantization method and the variable-rate step dequantization method, and
wherein the fixed-rate step dequantization method is a dequantization method in which the increment in the quantization step depending on the increase in the value of the quantization parameter by 1 is fixed.
8. The decoding method of claim 7 , wherein the increment in the quantization step of the variable-rate step dequantization method is less than the increment in the quantization step of the fixed-rate step dequantization method in a region in which the value of the quantization parameter is relatively large.
9. The decoding method of claim 7 , wherein:
a quantization parameter of the fixed-rate step dequantization method corresponding to the quantization parameter of the variable-rate step dequantization method is determined, and
a quantization step corresponding to the quantization parameter of the fixed-rate step dequantization method is used for the dequantization.
10. The decoding method of claim 7 , wherein:
a quantization step of the fixed-rate step dequantization method corresponding to the quantization parameter is determined based on the fixed-rate step dequantization method, and a quantization step of the variable-rate step dequantization method is determined by applying a quantization step rate to the quantization step of the fixed-rate step dequantization method, and
the quantization step rate is a ratio between the quantization step of the variable-rate step dequantization method and the quantization step of the fixed-rate step dequantization method.
11. The decoding method of claim 5 , further comprising acquiring a quantization method indicator,
wherein the quantization method indicator indicates one dequantization method to be used for dequantization of a target block among the multiple dequantization methods.
12. The decoding method of claim 11 , wherein the quantization method indicator indicates a dequantization method to be applied to a specific unit.
13. The decoding method of claim 12 , wherein the specific unit is a video, a sequence, a picture or a slice.
14. The decoding method of claim 12 , wherein the quantization method indicator indicates whether the variable-rate step dequantization method is applied to the specific unit.
15. The decoding method of claim 5 , wherein the quantization parameter difference value is included in a header of the lower unit.
16. The decoding method of claim 5 , wherein the upper unit is a picture and the lower unit is a slice.
17. A non-transitory computer-readable storage medium storing a bitstream comprising a computer-executable code for video decoding, the computer-executable code, when executed, causing a decoding device to perform the following steps:
acquiring a quantization parameter using a quantization parameter difference value from the bitstream; and
performing dequantization that uses a dequantization method,
wherein the dequantization method is a variable-rate step dequantization method,
wherein the variable-rate step dequantization method is a dequantization method in which an increment in a quantization step depending on an increase in a value of a quantization parameter by 1 is not fixed,
wherein the quantization parameter is acquired using the quantization parameter difference value,
wherein the quantization parameter is used for the dequantization,
wherein the quantization parameter difference value is a difference between a median value and the value of the quantization parameter or a difference between a value of a quantization parameter in an upper unit and a value of a quantization parameter in a lower unit to be used for the dequantization for the lower unit, and
wherein the median value is an intermediate value falling within a range of the quantization parameter of the variable-rate step dequantization method.