Modified quantizer

1. A method of video decoding using at least one processor, the method comprising:

obtaining video data including a syntax element indicating a quantization index;

parsing the syntax element to determine the quantization index;

adding an offset value to the quantization index;

obtaining a quantization step size from a lookup table based on the quantization index and the offset value; and

decoding the video data based on the quantization step size,

wherein based on the quantization index being smaller than a threshold value, the quantization step size based on a linear mapping with the quantization index and the offset value, and

wherein based on the quantization index being larger than the threshold value, the quantization step size based on an exponential mapping with the quantization index and the offset value.

2. The method of claim 1 , wherein the offset value is determined based on an internal bit depth value of the video data.

3. The method of claim 2 , wherein the quantization step size is obtained from the lookup table based on a result of adding the offset value to the quantization index, if the quantization index is larger than the threshold value.

4. The method of claim 1 , wherein the offset value is a negative integer.

5. The method of claim 1 , wherein the threshold value is 255.

6. The method of claim 1 , wherein the syntax element comprises a 9-bit integer.

7. The method of claim 1 , wherein a value of the 9-bit integer is equal to a result of adding the offset value to the quantization index.

8. The method of claim 1 , wherein a size of the lookup table is 255 values of the quantization step size.

9. A device for video decoding, the device comprising:

at least one memory configured to store program code; and

at least one processor configured to read the program code and operate as instructed by the program code, the program code including:

first obtaining code configured to cause the at least one processor to obtain video data including a syntax element indicating a quantization index;

parsing code configured to cause the at least one processor to parse the syntax element to determine the quantization index;

adding code configured to cause the at least one processor to add an offset value to the quantization index;

second obtaining code configured to cause the at least one processor to obtain a quantization step size from a lookup table based on the quantization index and the offset value; and

decoding code configured to cause the at least one processor to decode the video data based on the quantization step size,

wherein based on the quantization index being smaller than a threshold value, the quantization step size based on a linear mapping with the quantization index and the offset value, and

wherein based on the quantization index being larger than the threshold value, the quantization step size based on an exponential mapping with the quantization index and the offset value.

10. The device of claim 9 , wherein the offset value is determined based on the internal bit depth value of the video data.

11. The device of claim 10 , wherein the quantization step size is obtained from the lookup table based on a result of adding the offset value to the quantization index, if the quantization index is larger than the threshold value.

12. The device of claim 9 , wherein the offset value is a negative integer.

13. The device of claim 9 , wherein the threshold value is 255.

14. The device of claim 9 , wherein the syntax element comprises a 9-bit integer.

15. The device of claim 14 , wherein a value of the 9-bit integer is equal to a result of adding the offset value to the quantization index.

16. The device of claim 9 , wherein a size of the lookup table is 255 values of the quantization step size.

17. A non-transitory computer-readable medium storing instructions, the instructions comprising: one or more instructions that, when executed by one or more processors of a device for video decoding, cause the one or more processors to:

obtain video data including a syntax element indicating a quantization index;

parse the syntax element to determine the quantization index;

add an offset value to the quantization index;

obtain a quantization step size from a lookup table based on the quantization index and the offset value; and

decode the video data based on the quantization step size,

wherein based on the quantization index being smaller than a threshold value, the quantization step size based on a linear mapping with the quantization index and the offset value, and

wherein based on the quantization index being larger than the threshold value, the quantization step size based on an exponential mapping with the quantization index and the offset value.

18. The non-transitory computer-readable medium of claim 17 , wherein the offset value is determined based on a internal bit depth value of the video data.

19. The non-transitory computer-readable medium of claim 18 , wherein the quantization step size is obtained from the lookup table based on a result of adding the offset value to the quantization index, if the quantization index is larger than the threshold value.

20. The non-transitory computer-readable medium of claim 17 , wherein the syntax element comprises a 9-bit integer.