Method for decoding image and apparatus therefor

1. An image decoding method, performed by a decoding apparatus, the method comprising:

obtaining image information; and

generating a reconstructed picture based on the image information,

wherein the obtaining the image information comprises:

obtaining a flag representing whether one chroma quantization parameter table is applied or not; and

obtaining at least one chroma quantization parameter table based on the flag,

wherein the flag equal to 0 represents that a first chroma quantization parameter table for a Cb component, a second chroma quantization parameter table for a Cr component, and a third chroma quantization parameter table for a joint CbCr component are signaled.

2. The image decoding method of claim 1 , wherein the flag equal to 1 represents that the one chroma quantization parameter table is signaled and applies to the Cb component, the Cr component, and the joint CbCr component.

3. The image decoding method of claim 1 , wherein first chroma quantization parameter data comprises a syntax element representing a start index of the first chroma quantization parameter table and a syntax element representing a difference between the start index and a last index of the first chroma quantization parameter table.

4. The image decoding method of claim 3 , wherein the first chroma quantization parameter data comprises syntax elements for quantization parameter values of indices of the first chroma quantization parameter table.

5. The image decoding method of claim 3 , wherein second chroma quantization parameter data comprises a syntax element representing a start index of the second chroma quantization parameter table and a syntax element representing a difference between the start index and a last index of the second chroma quantization parameter table.

6. The image decoding method of claim 5 , wherein the second chroma quantization parameter data comprises syntax elements for quantization parameter values of indices of the second chroma quantization parameter table.

7. An image encoding method, performed by an encoding apparatus, the method comprising:

encoding image information; and

generating a bitstream including the image information,

wherein encoding the image information comprises:

generating a flag representing whether one chroma quantization parameter table is applied or not;

generating at least one chroma quantization parameter table based on the flag; and

encoding the at least one chroma quantization parameter table and the flag,

wherein the flag equal to 0 represents that a first chroma quantization parameter table for a Cb component, a second chroma quantization parameter table for a Cr component, and a third chroma quantization parameter table for a joint CbCr component are signaled.

8. A transmission method of data for image, the method comprising:

obtaining a bitstream of image information including a flag and at least one chroma quantization parameter table; and

transmitting the data including the bitstream of the image information including the flag and the at least one chroma quantization parameter table,

wherein the flag represents whether one chroma quantization parameter table is applied or not,

wherein the at least one chroma quantization parameter table is generated based on the flag, and

wherein the flag equal to 0 represents that a first chroma quantization parameter table for a Cb component, a second chroma quantization parameter table for a Cr component, and a third chroma quantization parameter table for a joint CbCr component are signaled.