Converting BT.2020 down to BT.709

[THRobinson]

I have a TCL 55" 55R615 plugged into an Android box, that I bypassed the OS with using an SD card running CoreElec w/Kodi.

Simple setup... Android plugged into TV HDMI, TV into Sony soundbar with HDMI (ARC).

Lately I started upgrading some movies to 4k 10bit. Big budget SciFi CGI stuff mostly, and saw a post about changing the TV settings from auto detect to HDMI2.0 or it may not switch to 4k. Got that all sorted out and 4k is working as it should, but then I noticed some movies brought up an HDR logo in the corner for a few seconds. Took a while to figure out, but, looks like the 10bit movies that are BT.2020 (newer standard?) envoke the HDR switch, and switches my TV picture mode.

I matched the setting for the new mode as much as I could with the regular mode I use and for the most part it looks good, but the reds/pinks are outta whack. Trying to watch the new remastered Back to the Future, and everyone looks like they've been brutally slapped in the face. Tried Fury Road, and the dessert is so pink/orange it looks like the movie was filmed just before the sun went down. I switch to my old 1080p versions, and the colours are perfect.

Some 4k I have is BT.709 and I think looks ok, though Marvel movies and they had a lot of grey filters.

I'm using VidCoder (same as Handbrake but, personally I find an easier GUI with a few more options). Is there a way to convert the video down to BT.709 so I can compare?

I saw a few posts on the ROKU site, people with the same issue, though didn't get as far as I did in what exactly envokes it... thinking although says it's BT.2020 compatible, maybe not as compatible as it could be. Saw a review that said something about handling about 70-80% of BT.2020... can't re-find the link, but maybe the issue?

When it doesn't switch to HDR, seems fine, when it does... reds/pinks outta whack. Tried adjusting colour/tint etc, no luck... Any ideas? otherwise, can I downgrade it to BT.709?

[ProWo]

Post a small sample of your 4k 10bit BT.2020 video here (10 sec)

[davexnet]

Post a small sample of your 4k 10bit BT.2020 video here (10 sec)

See this thread for some info
https://forum.videohelp.com/threads/391222-4K-H265-Soft-Display-Problem

[ProWo]

@davexnet
Thanks for the info

[hello_hello]

For the record, rec.2020 doesn't support HDR. That's a rec.2100 thing.
https://en.wikipedia.org/wiki/Rec._2100

Saw a review that said something about handling about 70-80% of BT.2020... can't re-find the link, but maybe the issue?

Most displays are RGB and rec.2020 uses a wider color gamut. I suspect that's where the 70%-80% thing comes from. It shouldn't be causing your problem though. Rec.2020 & Rec.2100 use the same color space.
Rec.709 / sRGB
https://upload.wikimedia.org/wikipedia/commons/e/ef/CIExy1931_Rec_709.svg
Rec.2020
https://upload.wikimedia.org/wikipedia/commons/b/b6/CIExy1931_Rec_2020.svg

I know nothing about how HDR works in respect to it being automatically enabled or not, so I can't help you there.

[THRobinson]

Sorry for the delay....

Here's a clip, no audio to make the size smaller. Trying to figure out how to screen cap on KODI. My old remote had a button but this remote doesn't.

On my screen I can hit pause/info and the main screen image has the red "slapped face" look, while the thumbnail at the bottom of the same scene, is neutral coloured.

[davexnet]

Sorry for the delay....

Here's a clip, no audio to make the size smaller. Trying to figure out how to screen cap on KODI. My old remote had a button but this remote doesn't.

On my screen I can hit pause/info and the main screen image has the red "slapped face" look, while the thumbnail at the bottom of the same scene, is neutral coloured.

Kodi on the PC?
Can't you just hit the print screen button on the keyboard?

Thanks for HDR sample; color doesn't look particularly natural on my TV,
but I can say that about quite a few of the HDR videos I've seen on it, flesh tones often a bit dodgy.

Low end LG TV, I guess it does the best it can with the tone mapping

[hello_hello]

My first HDR to SDR conversion, probably not done correctly, but it's as close as I could get before the desire to kill myself became too hard to resist. It was unbelievably slow to do on my old PC. Conversion with HDRTools.

Rec.2020 to Rec.709

CropResize(960,540)
ConvertBits(16)
ConvertToYUV444()
ConvertYUVtoXYZ(Color=1)
ConvertXYZtoYUV(Color=2, PColor=1)
ConvertBits(8)


[Attachment 55688 - Click to enlarge]


Rec.2020/21 to Rec.709, crossing my fingers and including HDR to SDR conversion

CropResize(960,540)
ConvertBits(16)
ConvertToYUV444()
ConvertYUVtoXYZ(Color=0, HDRMode=0)
ConverXYZ_BT2446_C_HDRtoSDR(PQMode=true)
ConvertXYZtoYUV(Color=2, PColor=0)
ConvertBits(8)


[Attachment 55689 - Click to enlarge]


[Attachment 55690 - Click to enlarge]

Does the way it displays on your TV look like either of the above?

[THRobinson]

On my TV... it looks like the 2nd image except mine has more reddish blotchiness in the skin which is what I'm trying to tone down.

I have KODI running on an Android box, my remote has a keyboard but no ctrl button or print screen button since not a full keyboard. I'll have to dig an old keyboard out maybe, though not sure it'll matter... screen capture will capture what the software see's on the screen not what my eye is seeing, plus I'll then be showing the image on whatever screen you/I have on the PC so... ya... I'm thinking screen shots may be useless for this situation.

[davexnet]

On my TV... it looks like the 2nd image except mine has more reddish blotchiness in the skin which is what I'm trying to tone down.

I have KODI running on an Android box, my remote has a keyboard but no ctrl button or print screen button since not a full keyboard. I'll have to dig an old keyboard out maybe, though not sure it'll matter... screen capture will capture what the software see's on the screen not what my eye is seeing, plus I'll then be showing the image on whatever screen you/I have on the PC so... ya... I'm thinking screen shots may be useless for this situation.

Here's the quick re-encode, rec 709 conversion, using DGReinhard

[THRobinson]

So... where'd we land on this one?

How do I convert from BT.2020 to BT.709? or HDR to SDR?

[davexnet]

So... where'd we land on this one?

How do I convert from BT.2020 to BT.709? or HDR to SDR?

Install Avisynth Plus, create your script, encode in Vdub2.
This is the script I used for the above example:

dss2("C:\Users\davex\Downloads\Back to the Future (1985) 4k 10bit - 0.10.35-0.11.35.mkv") # instead of dss2 you can use LWLibAvVideoSource
spline36resize(1280,692)    #    optional resize
ConvertBits(10) # Use 12 for 12-bit
z_ConvertFormat(pixel_type="RGBPS",colorspace_op="2020ncl:st2084:2020:l=>rgb:linear:2020:l", dither_type="none")
# Choose one of these:
DGReinhard()
#DGHable()
z_ConvertFormat(pixel_type="YV12",colorspace_op="rgb:linear:2020:l=>709:709:709:l",dither_type="ordered")

Here's the links for the tonemap plugin and Lsmash/LWLibAv source filter
http://avisynth.nl/index.php/DGTonemap
https://github.com/HolyWu/L-SMASH-Works/releases/

[sneaker]

I have a TCL 55" 55R615

Some TCL TVs have horrible HDR defaults. Instead of re-encoding you might try:
- Setting TV picture settings to "PC mode" when viewing HDR content
- Update to latest TV firmware. Afterwards reset nvm + reset shop via the hidden menu. At least for some models they changed the HDR processing but it might need the resets.

(If this applies to your particular model: I don't know.)

[THRobinson]

@davexnet and @sneaker

Thanks... I'll try the PC Mode first and see how it looks.

I've been grabbing samples of the same movie for comparison, and that BT.2020 10bit is just awful for me. Looks like oversaturated red/orange with a grey overlay. Kinda blotchy. But other versions from the same source definitely look better. SD looks grey and dull, but 10bit SDR looks pretty good.

[AndiSeb]

Did you try using a BT.2020 to Rec.709 conversion LUT in a video editing software? I imagine this could do the job https://cc-lut.hotglue.me/

[THRobinson]

I basically decided that BT.2020 HDR on my TV at least, looks bad. Grey with colour glowing out from underneath... like HDR photography done by an amateur.

10bit BT.709 seems to be fine so, been making sure my sources are that.