Decoding device and decoding method, and coding device and coding method

1. A decoding device comprising:

circuitry configured to

receive coded data and conversion information, the coded data pertaining to an image having luminance in a first dynamic range and the conversion information pertaining to a conversion of dynamic range of the luminance of the image from the first dynamic range into a second dynamic range; and

decode the received coded data so as to generate the image,

wherein the conversion uses a knee function that is defined by the connecting of a plurality of knee points in a set order, each knee point of the knee function being located at a respective coordinate that is defined by a respective input knee point and a respective output knee point, the respective input knee point specifying a luminance level of the knee point at the respective coordinate for the image of the first dynamic range, and the respective output knee point specifying a luminance level of the knee point at the respective coordinate for the image of the second dynamic range after the conversion.

2. The decoding device according to claim 1 , wherein the conversion uses the knee function to map the dynamic range of the luminance of the image from the first dynamic range into the second dynamic range.

3. The decoding device according to claim 2 , wherein the conversion information includes pre-conversion information and post-conversion information,

wherein the pre-conversion information indicates a range of luminance in the first dynamic range, and

wherein the post-conversion information indicates a range of luminance in the second dynamic range that corresponds to the range of luminance indicated by the pre-conversion information.

4. The decoding device according to claim 3 , wherein the pre-conversion information indicates the range of luminance which is converted by knee function at a same conversion ratio as a conversion range of the first dynamic range.

5. The decoding device according to claim 3 , wherein the conversion information includes a plurality of pairs of the pre-conversion information and the post-conversion information.

6. The decoding device according to claim 1 , wherein the conversion uses the knee function by mapping the dynamic range of the luminance of the image from the first dynamic range into the second dynamic range, and a plurality of adjacent segments of the first dynamic range of the luminance are mapped to a corresponding plurality of adjacent segments of the second dynamic range of the luminance based on boundaries between adjacent segments defined by the plurality of knee points.

7. The decoding device according to claim 2 , wherein the conversion uses the knee function by mapping the dynamic range of the luminance of the image from the first dynamic range into the second dynamic range at a first conversion ratio to a point defined by the at least one knee point and at a second conversion ratio from the point defined by the at least one knee point.

8. The decoding device according to claim 1 , wherein the knee function is specified by a Supplemental Enhancement Information (SEI) message.

9. The decoding device according to claim 8 , wherein the SEI message includes a setting of a knee_function_id.

10. A decoding method of causing a decoding device to perform:

receiving coded data and conversion information, the coded data pertaining to an image having luminance in a first dynamic range and the conversion information pertaining to a conversion of dynamic range of the luminance of the image from the first dynamic range into a second dynamic range; and

decoding the received coded data so as to generate the image,

wherein the conversion uses a knee function that is defined by the connecting of a plurality of knee points in a set order, each knee point of the knee function being located at a respective coordinate that is defined by a respective input knee point and a respective output knee point, the respective input knee point specifying a luminance level of the knee point at the respective coordinate for the image of the first dynamic range, and the respective output knee point specifying a luminance level of the knee point at the respective coordinate for the image of the second dynamic range after the conversion.

11. The decoding method according to claim 10 , wherein the conversion information includes pre-conversion information indicating a range of luminance in the first dynamic range and post-conversion information indicating a range of luminance in the second dynamic range that corresponds to the range of luminance indicated by the pre-conversion information.

12. The decoding method according to claim 11 , wherein the pre-conversion information indicates the range of luminance which is converted by knee function at a same conversion ratio as a conversion range of the first dynamic range.

13. The decoding method according to claim 11 , wherein the conversion information includes a plurality of pairs of the pre-conversion information and the post-conversion information.

14. The decoding method according to claim 10 , wherein the conversion uses the knee function by mapping the dynamic range of the luminance of the image from the first dynamic range into the second dynamic range at a first conversion ratio to a point defined by at least one knee point of the plurality of knee points and at a second conversion ratio from the point defined by the at least one knee point.

15. A coding device comprising:

circuitry configured to

set conversion information pertaining to a conversion of dynamic range of a luminance of an image from a first dynamic range into a second dynamic range; and

code the image having luminance in the first dynamic range so as to generate coded data,

wherein the conversion uses a knee function that is defined by the connecting of a plurality of knee points in a set order, each knee point of the knee function being located at a respective coordinate that is defined by a respective input knee point and a respective output knee point, the respective input knee point specifying a luminance level of the knee point at the respective coordinate for the image of the first dynamic range, and the respective output knee point specifying a luminance level of the knee point at the respective coordinate for the image of the second dynamic range after the conversion.

16. The coding device according to claim 15 , wherein the conversion information includes pre-conversion information indicating a range of luminance in the first dynamic range and post-conversion information indicating a range of luminance in the second dynamic range that corresponds to the range of luminance indicated by the pre-conversion information.

17. The coding device according to claim 16 , wherein the pre-conversion information indicates the range of luminance which is converted by knee function at a same conversion ratio as a conversion range of the first dynamic range.

18. The coding device according to claim 16 , wherein the conversion information includes a plurality of pairs of the pre-conversion information and the post-conversion information.

19. The decoding device according to claim 1 , wherein the conversion information includes conversion persistence information which is information indicating whether or not the conversion information is applied to a plurality of continuous pictures.

20. The decoding device according to claim 1 , wherein the plurality of knee points specify conversion ratios at respective points of the knee function used for the conversion of the dynamic range.

21. The decoding device according to claim 1 , wherein each knee point of the plurality of knee points specifies a coordinate position that associates a respective value of luminance of the image before conversion to a respective value of luminance of the image after conversion.

22. A non-transitory computer-readable medium having stored thereon coded data and conversion information, the coded data pertaining to an image having luminance in a first dynamic range and the conversion information pertaining to a conversion of dynamic range of the luminance of the image from the first dynamic range into a second dynamic range, wherein

when a decoding device decodes the coded data, the decoding device is caused to generate the image based on the decoded data, and also caused to convert, using a knee function that is defined by the connecting of a plurality of knee points in a set order, the dynamic range of the luminance of the image from the first dynamic range into a second dynamic range based on the conversion information, each knee point of the knee function being located at a respective coordinate that is defined by a respective input knee point and a respective output knee point, the respective input knee point specifying a luminance level of the knee point at the respective coordinate for the image of the first dynamic range, and the respective output knee point specifying a luminance level of the knee point at the respective coordinate for the image of the second dynamic range after the conversion.

23. The decoding device according to claim 1 , wherein the knee function is defined by connecting the knee points to each other in an ascending order.

24. The decoding device according to claim 1 , wherein data processing requirement is minimized by defining the knee function utilizing relationship between adjacent knee points.