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18th March 2024, 12:19 | #1 | Link |
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Subtitle colors (SUP/PGS) with Dolby Vision video
Hello.
Does anyone know what is the color conversion to use to have the expected color of SUP/PGS subtitles displayed with a DV video file ? It's not a "pure/only" DV, it's an HDR+DV. Actualy on my subtitles, the green is purple, the yellow is green, etc... Black and white are fine... If there is any formula convertion or anything similar, i'm interested.
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24th March 2024, 11:37 | #2 | Link |
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So, i've made the following experience.
Created a subtitle with this picture to display: And the result on a file with DV video is: I'll try to figure out the DV conversion matrix. Anyone is free to try also to figure out, i take any input.
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24th March 2024, 16:16 | #3 | Link |
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Would this only go for Dolby Vision Profile 5? When experiencing green & purple, usually P5 is in play. If so, I reckon it has to do with Dolby proprietary IPTPQc2 colorspace P5 video is encoded in.
Where P8 and P7 aren't. |
24th March 2024, 19:10 | #4 | Link |
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Video is played properly, it's just the subtitles which are messed up. Video is HDR10 compatible with DV data, so colorspace of video is standard HDR PQ, video is not the green & purple type.
Also, maybe it's a bug in the HW player, and it shouldn't apply DV "things" to color palette subtitles... But it is this way. Edit: Something pecular: There is displayed red,green,blue,cyan, magenta, but despite the fact i put all the colors combinations, there is no yellow ! I needed green and yellow colors subtitles, i don't know if it will even be possible...
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24th March 2024, 22:08 | #5 | Link | ||
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The first time I peek at the x265 subforum to find the right set of parameters to produce encodes for UHD BD, there HAS to be a thread about PGS at the top. Absolutely incredible.
How did you generate the PG stream? Some authoring tools do not seem particularly careful about the transfer matrix and so on. Furthermore: what is the PID of your subtitle file? It seems that 0x1200-121F are meant for SDR PGS, while 0x12A0-12BF are for HDR. As we lack UHD BD details, it is hard to know why they added additional PIDs for PGS, but it is probably related to this statement found in this technical review: Quote:
This is furthermore backed by: Quote:
Last edited by cubicibo; 25th March 2024 at 09:31. |
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25th March 2024, 09:29 | #6 | Link |
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This is not a Blu-Ray, this is an MKV file i'm making. I made myself the PGS/SUB. And it's not a BT.2020/BT.709 issue, this is DV specific. The same on a video without DV has the colors displayed properly.
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25th March 2024, 09:37 | #7 | Link |
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But how do you play back the file? Seems like your issue is either:
- Your software video player applies DV to subtitles. This is very much incorrect and this should be reported to the issue tracker of the player. - You use a BD player to read the file from a hard-drive. And as it is MKV, the player is unable to know if it should use the SDR or HDR PGS decoder (no PID information in MKV). And eventually it just defaults to SDR "before DV" blend. The fix is simply to use a transport stream container in that case. |
25th March 2024, 13:55 | #8 | Link |
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I play the file on my HW player, a Zappiti Neo.
And i also think that it shouldn't apply DV to subtitles... But i don't know the specs, and how it's supposed to do.
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25th March 2024, 14:29 | #9 | Link |
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This is not a Blu-ray Disc player, the manufacturer is not listed on the BDA licensee list: it most likely does not comply with the Blu-ray specifications and overlay the subtitles before the enhancement layer. File a bug report to Zappiti so they can fix their device.
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25th March 2024, 16:58 | #10 | Link | |
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Quote:
It's all very clever, but means decoding a Profile 5 base layer as normal Y'CbCr PQ 2020 looks really weird. I'm kind of thankful that it is weird enough that no one will think it's operating properly. Makes for easier debugging. |
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26th March 2024, 10:07 | #11 | Link |
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Reading the specs of this player, it runs on a Realtek RTD1619DR chipset. Same as my Zidoo Z9X. Which a couple of years ago also suffered from wrong subtitle colorings. This was brought up in the Zidoo forums, which are monitored by one of the Zidoo people. Consequently, firmware updates then ironed out the issue.
I can imagine your Zappiti having a similar firmware problem. Where letting Zappiti's customer-service folks know about it may trigger a fix? Last edited by von Suppé; 26th March 2024 at 10:18. |
26th March 2024, 13:42 | #12 | Link |
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Probably.
In the meantime, i'll create two subtitles tracks, one with "normal" colors, one with "DV Mode" colors. I've tried to figure out if there was a linear matrix transform, like this: [Rdv,Gdv,Bdv]=[Matrix]*[R,G,B]. For now, i've guessed the following, according the display result: [R,G,B] -> [Rdv,Gdv,Bdv] [1,0,0] -> [0.5,0.25,0] [0.5,0,0] -> [0.25,0.125,0] [0,0,1] -> [0.5,0,0.25] [0,0,0.5] -> [0.25,0,0.125] But, after some others guess, it seems that's clearly it's not so simple/linear... So, i'll have to try the other method: test/experiment, what color produces the display i expect. As it's for subtitles, i don't need true accurate, but something which "looks like". If something looks like green, even if not "pure green", it will be enough. I can produce basic colors, or at least something which looks like : Red, Green, DarkGreen, Blue, Cyan, Magenta... And i need (except Black/White) Greend, DarkGreen, Yellow... But... Where is yellow ???? I "only" tried 1 & 0.5 combinations with only 1 or 2 values (like [1,0,0] or [0,0.5,0] or [1,0.5,0]). Didn't tried yet things like [1,0.5,0.5] or [1,1,0.5]... Maybe i'll be able to discover what produces a yellow display. It's not so a linear combination, because according display, it seems: [1,1,0] -> [0,1,0] and [1,0,1] -> [1,0,0] So... [2,1,1] -> [1,1,0].... But [1,0.5,0.5] could be worth trying, because it wasn't in my first picture, so, who knows...
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My github. Last edited by jpsdr; 26th March 2024 at 13:48. |
26th March 2024, 15:16 | #13 | Link |
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Did you try LMS? AFAIK Dolby Vision is transformed and transmitted in that colorspace.
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Yesterday, 15:05 | #15 | Link |
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I took a look at LMS, from the few i understood, there is 3 (at least) differents: Equal-energy illuminants, Normalized to D65 and physiological CMFs.
Any idea, by any chance, which one it could be ?
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Yesterday, 17:56 | #16 | Link | |
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Quote:
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