sofakng wrote: ↑Mon Jul 18, 2022 2:22 am
Are there any ELI5 (explain like I'm five) guides for Dolby Vision?
I've tried searching but I can't find anything really straightforward to explain RPU, MEL, FEL, etc.
I'm very amateur, this is for reference only, it may contain mistakes.
Once upon a time, cats only use 0-255 to represent brightness of themselves. Black cat is 0 and white cat is 255. This is called SDR.
And then there is a 5-year-old cat Tom, who is a grey cat with a little blue. His color is somewhere around 255/2 in the middle. Tom likes to take selfie with his friends on his 300 nit iPhone. Since the display brightness back then were close to each other, with no more than 400 nit, it seems fine for Tom to tell himself from other cat.
But one day, Tom bought a 1000 nit Samsung tv home and started to enjoy his good old selfies. He immediately noticed he is whiter(500 nit) in the TV than himself in the mirror(250 nit). He also noticed his good old selfies are slightly darker(150 nit) in his iPhone. He became a white cat in his Samsung tv and a dark blue cat on his iPhone. What's worse, he found himself a 5000-nit glowing cat on a 10000-nit experimental monitor.
"This can't be good." he thought. So he gathered all other cats to make a new standard. They use 0 to represent 0 nit completely dark black hole cat, somewhere between 700-750 to represent 1000-nit snow-white cat, and 1023 to represent 10000-nit dazzling Apollo cat who lives on the sun. And now Tom can finally be the same grey blue cat. This is called PQ curve HDR bl(base layer).
PQ_curve_code_value_vs._luminance.jpg
As time went by, Tom gradually grows fond of those >1000 nit snow-white cats. However they all appear to be idendical white on his 1000 nit tv. He doesn't want to mess up with the Apollo cat. Thankfully, Dolby provides RPU(reference processing unit) to indicate how cats above 1000 nit should exactly display on Tom's tv and phone. (tone mapping). It also provides EL(enhancement layer) to generate even more accurate 12-bit color depth. And now Tom can know exactly which cat is which. Yet there are so many profiles and unknown specifics, Tom has to post and ask about Dolby Vision here.
In human words:
BL(base layer): an HDR10 2160p YCbCr 4:2:0 10-bit video.
Dolby Vision fall back to this when not supported.
EL(enhancement layer): an HDR10 1080p YCbCr 4:2:0 10-bit video.
Supported device use BL and EL to mux a final 4:2:2 12-bit video.
RPU(reference processing unit): To indicate how filmmaker would like the video to be separately shown on 100nitSDR/600nit/1000nit/10000nit display. (despite the actual brightness record in BL)
There are basically 4 types of Dolby Vision video:
Profile 5(streaming): ICtCp 4:2:0(?) 10-bit video + RPU.
It uses a more efficient color coding, but appear green and purple on non support device.
Profile 8.1: BL+RPU
Profile 8.4: Dolby Vision shot on iPhone, HLG BL+RPU
FEL(Full Enhancement Layer)
Profile 7 DT_DL FEL: BL in one video track, EL+RPU in another video track.
Profile 7 ST_DL FEL: BL+EL+RPU in one same video track.
MEL(Minimum Enhancement Layer)
Profile 7 MEL: BL+RPU same as 8.1 just in bluray container.
Please don't hesitate to point out my mistake!