I'm going to be heavily referencing this white paper from Dolby: https://www.dolby.com/us/en/technologies/dolby-vision/dolby-vision-white-paper.pdf
"The Dolby Vision HDR reference monitor (capable of up to 4,000 nits luminance) is used to make the color and brightness decisions... After the reference color grade is finished, the Dolby Vision color-grading system will analyze and save the dynamic metadata that describes the creative decisions made on the display. The content mapping unit (CMU) maps the content with the metadata to a reference display at a standard brightness (100 nits).
The dynamic metadata generated to create the SDR grade can be used to render the Dolby Vision master on displays... [all] referencing the same metadata and Dolby Vision reference images."
So basically, the DV metadata describes a transform from the HDR10 grade down to an SDR grade for each frame of the film. Dolby's characterization of a manufacturer's display is used to make the DV hardware which uses the transform in the meta-data to perform it "part way"... down from 4000 max nits to 1000 max nits (vs 100) for example.
So what about the 10 bit HD resolution Dolby vision layer that's bundled with the 10 bit base layer 4K video stream? The white paper, on page 11, describes this as the enhancement stream but does not say what it is specifically... does it add the data necessary to bring the base layer 10 bit file to a 12 bit file? If so, why is it at 1/4 the resolution of the base layer? Also, if so, why does a single layer Dolby Vision solution only require a 10 bit file?
Other Dolby lit mentions that the "Dolby Vision dual-layer backward-compatible solution includes an uncompromised SDR Rec. 709 signal." Given that the color information in 4K 4:2:0 video is 1/4 the resolution of the non color information, does this mean that the enhancement layer contains the SDR REC709 color data from the SDR grade? If so, why does does this (along with the meta data) need to be combined with the HDR base layer to create what Dolby describes as the "full-range signal" (in 12 bits of course)?
Would appreciate it if someone in the know could straighten out my naivety and errors in these regards!
On an aside, it really seems like Dolby Vision is the best HDR standard out of any available.
-It requires grading on Dolby Displays, creating a reference standard.
-It allows the colorist to specifically define how the HDR image is to be represented on SDR displays; no leaving it up to display manufacturers.
-Dolby characterizes certified displays and creates custom software to ensure that the conversions are done properly.
-Dolby claims that the 12 bit full range signal drastically reduces the potential for banding and stepping on 10k nit systems.
HDR10+ brings the HDR to SDR metadata to allow the colorist some more control, but because there's no grading display standardization, no standard hardware across display manufacturers... it seems like a free for all that will result in a LOT more variability from display to display, and it also seems like some studios and display manufacturers are opting for it simply because they are cheap and don't want to pay Dolby for the hard work they have done (worth noting that Dolby developed the HDR10 spec, and doesn't see a dime for that).
"The Dolby Vision HDR reference monitor (capable of up to 4,000 nits luminance) is used to make the color and brightness decisions... After the reference color grade is finished, the Dolby Vision color-grading system will analyze and save the dynamic metadata that describes the creative decisions made on the display. The content mapping unit (CMU) maps the content with the metadata to a reference display at a standard brightness (100 nits).
The dynamic metadata generated to create the SDR grade can be used to render the Dolby Vision master on displays... [all] referencing the same metadata and Dolby Vision reference images."
So basically, the DV metadata describes a transform from the HDR10 grade down to an SDR grade for each frame of the film. Dolby's characterization of a manufacturer's display is used to make the DV hardware which uses the transform in the meta-data to perform it "part way"... down from 4000 max nits to 1000 max nits (vs 100) for example.
So what about the 10 bit HD resolution Dolby vision layer that's bundled with the 10 bit base layer 4K video stream? The white paper, on page 11, describes this as the enhancement stream but does not say what it is specifically... does it add the data necessary to bring the base layer 10 bit file to a 12 bit file? If so, why is it at 1/4 the resolution of the base layer? Also, if so, why does a single layer Dolby Vision solution only require a 10 bit file?
Other Dolby lit mentions that the "Dolby Vision dual-layer backward-compatible solution includes an uncompromised SDR Rec. 709 signal." Given that the color information in 4K 4:2:0 video is 1/4 the resolution of the non color information, does this mean that the enhancement layer contains the SDR REC709 color data from the SDR grade? If so, why does does this (along with the meta data) need to be combined with the HDR base layer to create what Dolby describes as the "full-range signal" (in 12 bits of course)?
Would appreciate it if someone in the know could straighten out my naivety and errors in these regards!
On an aside, it really seems like Dolby Vision is the best HDR standard out of any available.
-It requires grading on Dolby Displays, creating a reference standard.
-It allows the colorist to specifically define how the HDR image is to be represented on SDR displays; no leaving it up to display manufacturers.
-Dolby characterizes certified displays and creates custom software to ensure that the conversions are done properly.
-Dolby claims that the 12 bit full range signal drastically reduces the potential for banding and stepping on 10k nit systems.
HDR10+ brings the HDR to SDR metadata to allow the colorist some more control, but because there's no grading display standardization, no standard hardware across display manufacturers... it seems like a free for all that will result in a LOT more variability from display to display, and it also seems like some studios and display manufacturers are opting for it simply because they are cheap and don't want to pay Dolby for the hard work they have done (worth noting that Dolby developed the HDR10 spec, and doesn't see a dime for that).
