Adaptive transfer function for video encoding and decoding
A video encoding and decoding system that implements an adaptive transfer function method internally within the codec for signal representation. A focus dynamic range representing an effective dynamic range of the human visual system may be dynamically determined for each scene, sequence, frame, or region of input video. The video data may be cropped and quantized into the bit depth of the codec according to a transfer function for encoding within the codec. The transfer function may be the same as the transfer function of the input video data or may be a transfer function internal to the codec. The encoded video data may be decoded and expanded into the dynamic range of display(s). The adaptive transfer function method enables the codec to use fewer bits for the internal representation of the signal while still representing the entire dynamic range of the signal in output.
1 . A system, comprising:
a video encoder, configured to perform operations comprising:
accessing a plurality of frames of source video data and a plurality of transfer functions used to map a full dynamic range of the source video data to a focus range of luminance values of the source video data;
for each frame of the plurality of frames:
selecting a particular transfer function of the plurality of transfer functions, and
determining particular luminance values of the frame using the focus range of luminance values and the particular transfer function, wherein different transfer functions of the plurality of transfer functions are used corresponding to the plurality of frames;
encoding a plurality of particular luminance values determined for the plurality of frames into encoded video data;
generating format metadata providing information on the focus range luminance values and the plurality of transfer functions; and
generating a bit stream comprising the encoded video data and the format metadata.
2 . The system of claim 1 , wherein the plurality of transfer functions includes (i) a first transfer function configured to crop source video data corresponding to a frame of the plurality of frames according to a focus range of the source video data corresponding to the frame, and (ii) a second transfer function configured to map the cropped source video data corresponding to the frame into an available number of bits used to represent the encoded video data.
3 . The system of claim 2 , wherein the source video data and the encoded video data are represented using different numbers of bits, and
wherein a first number of bits used to represent the source video data is greater than a second number of bits used to represent the encoded video data.
4 . The system of claim 3 , wherein a decoder is configured to decode the encoded video data obtained from the bit stream using a third number of bits that is different than the first number of bits or the second number of bits.
5 . The system of claim 2 , wherein a first number of frames of the plurality of frames are encoded using one or more portions of the first transfer function and a second number of frames of the plurality of frames are encoded using the second transfer function.
6 . The system of claim 5 , wherein the format metadata includes information indicating the one or more portions of the first transfer function.
7 . The system of claim 1 , wherein a first transfer function and a different second transfer function of the plurality of transfer functions are respectively used for a first frame and a second frame of the plurality of frames.
8 . The system of claim 7 , wherein the first frame and the second frame are adjacent frames of the source video data.
9 . A video encoding method comprising:
accessing a plurality of frames of source video data and a plurality of transfer functions used to map a full dynamic range of the source video data to a focus range of luminance values of the source video data;
for each frame of the plurality of frames:
selecting a particular transfer function of the plurality of transfer functions, and
determining particular luminance values of the frame using the focus range of luminance values and the particular transfer function, wherein different transfer functions of the plurality of transfer functions are used corresponding to the plurality of frames;
encoding a plurality of particular luminance values determined for the plurality of frames into encoded video data;
generating format metadata providing information on the focus range luminance values and the plurality of transfer functions; and
generating a bit stream comprising the encoded video data and the format metadata.
10 . The method of claim 9 , wherein the plurality of transfer functions includes (i) a first transfer function configured to crop source video data corresponding to a frame of the plurality of frames according to a focus range of the source video data corresponding to the frame, and (ii) a second transfer function configured to map the cropped source video data corresponding to the frame into an available number of bits used to represent the encoded video data.
11 . The method of claim 10 , wherein the source video data and the encoded video data are represented using different numbers of bits, and
wherein a first number of bits used to represent the source video data is greater than a second number of bits used to represent the encoded video data.
12 . The method of claim 11 , wherein a decoder is configured to decode the encoded video data obtained from the bit stream using a third number of bits that is different than the first number of bits or the second number of bits.
13 . The method of claim 10 , wherein a first number of frames of the plurality of frames are encoded using one or more portions of the first transfer function and a second number of frames of the plurality of frames are encoded using the second transfer function.
14 . The method of claim 13 , wherein the format metadata includes information indicating the one or more portions of the first transfer function.
15 . The method of claim 9 , wherein a first transfer function and a different second transfer function of the plurality of transfer functions are respectively used for a first frame and a second frame of the plurality of frames,
wherein the first frame and the second frame are adjacent frames of the source video data.
16 . A non-transitory computer readable medium storing instructions that, when executed by one or more processors, cause a video encoder to perform operations comprising:
accessing a plurality of frames of source video data and a plurality of transfer functions used to map a full dynamic range of the source video data to a focus range of luminance values of the source video data;
for each frame of the plurality of frames:
selecting a particular transfer function of the plurality of transfer functions, and
determining particular luminance values of the frame using the focus range of luminance values and the particular transfer function, wherein different transfer functions of the plurality of transfer functions are used corresponding to the plurality of frames;
encoding a plurality of particular luminance values determined for the plurality of frames into encoded video data;
generating format metadata providing information on the focus range luminance values and the plurality of transfer functions; and
generating a bit stream comprising the encoded video data and the format metadata.
17 . The non-transitory computer readable medium of claim 16 , wherein the plurality of transfer functions includes (i) a first transfer function configured to crop source video data corresponding to a frame of the plurality of frames according to a focus range of the source video data corresponding to the frame, and (ii) a second transfer function configured to map the cropped source video data corresponding to the frame into an available number of bits used to represent the encoded video data.
18 . The non-transitory computer readable medium of claim 17 , wherein the source video data and the encoded video data are represented using different numbers of bits,
wherein a first number of bits used to represent the source video data is greater than a second number of bits used to represent the encoded video data, and
wherein a decoder is configured to decode the encoded video data obtained from the bit stream using a third number of bits that is different than the first number of bits or the second number of bits.
19 . The non-transitory computer readable medium of claim 18 , wherein a first number of frames of the plurality of frames are encoded using one or more portions of the first transfer function and a second number of frames of the plurality of frames are encoded using the second transfer function, and
wherein the format metadata includes information indicating the one or more portions of the first transfer function.
20 . The non-transitory computer readable medium of claim 16 , wherein a first transfer function and a different second transfer function of the plurality of transfer functions are respectively used for a first frame and a second frame of the plurality of frames, and
wherein the first frame and the second frame are adjacent frames of the source video data.