TCL C645 PC game mode / hdr guide

Jan 2nd 2025 Update: this topic about HDMI 2.1 seems so confusing I am sorry to once again have an update on this.
After I got another monitor I was going through the config on the TV in nvcp and suddenly I was able to select 1440p 10 bit RGB full and the TV was able to hold those settings so go figure!!!!. I was also able to select 4k60 with 10 bit RGB full. So I guess this TV is indeed HDMI 2.1 on one of its ports.
If I would have to guess I would say it was something with the nvidia drivers, I am now using nvidia driver 566.14. The only other update to my system is I got a 1440p HDR monitor capable of 10 bit but it is connected through DP.

UPDATE:
bought an HDMI 2.1 cable and I can confirm the max the TV can do with RGB Full 10 bit is 1080p. See detail below:
4k60 with VRR and HDR with RGB 8 bit Full + dithering or YUV 422 10 bit.
1440p120 with DLG VRR and RGB 8 bit Full or YUV 422 10 bit.
1080p120 with DLG can do HDR on RGB Full 10 bit. I have tried this and to be honest I don't see much of a difference with YUV 422 10 bit @ 1440p120
I am using YUV 422 12 bit with 2560x1440 and to be honest looks great. I am pretty sure the difference is minimal, check it for your self on either 1080p120 RGB 10 bit or 4k30 10 RGB bit, I bet you won't see the difference.
SOURCE: TCL's own spec sheet
https://www.tcl.com/content/dam/brandsite/region/australia/AU_Mediacenter/download/65C645_Product_Specifications_Final.pdf
The TV supports HDMI 2.1 features like eARC and VRR but does not have the HDMI 2.1 bandwidth to support 4k60 RGB 10 bit

Best experience after losing some nights testing different stuff out. Long text ahead warning.I just got a TCL C645 and I have a PC with a 2060 super through HDMI and this is my setup. After a lot of figuring stuff out and trying different stuff I am finally set on SDR and HDR gaming on my TCL TV.

  1. In the TV settings - Input settings - make sure the Advanced HDMI 2.1 or 2.0 compatible is enabled and ALLM (Auto Low Latency Mode) and VRR (freesync) are both enabled. If you are only interested in low input lag and vrr then this will work with PC Picture mode or with Game Picture Mode, follow on if you are interested in Game Master/HDR/Game Bar/HGiG
  2. In the TV settings - System - Enable Game Master (this is the tricky part, if you are in PC picture mode then you won't be able to do it, use Game Picture Mode and then try to enable Game Master) I am now not using Game Master since it is messing with my HDR/SDR settings and it is actually not needed.
  3. For SDR games make sure Use HDR is disabled in Windows display settings
  4. Following instructions relate only to HDR gaming and everyone knows HDR and Windows is a pain so this is what worked for me.
  5. Leave nvidia settings alone (RGB Full) for SDR games - YUV 422 10 bit for HDR games if limited by HDMI 2.0. If you have HDMI 2.1 card and cable then set to RGB Full / 10 or 12 bit. see update above
  6. Some games require the Display Settings flag of Use HDR to be enabled so figure this yourself on a game by game basis
  7. If you are using Reshade on a game you have to disable any effect, specially I had issues with CAS, but better to toggle the effects off for HDR as it completely destroyed the image for me.
  8. Once in a game and with HDR enabled take your time to calibrate using the in game HDR settings to best match your TV set
  9. Now the next step is subjective - You have 2 options (enable HGiG, if disabled then Dynamic Tone Mapping is enabled). Play around with those and stick with what looks better and it will certainly vary from game to game. To bring the HGiG option hold the TV remote button with the 3 lines to make Game Bar come up and enable/disable the setting. For the dynamic tone mapping find the setting in the Picture settings. HGiG and Dynamic tone mapping cannot be enabled at the same time AFAIK.Extra: just pressing the 3 line button on the remote gets you quick settings bar where you can check game master is on or off.
  10. Above setup and instructions is for gaming only, if you are going to use the TV for desktop then disable Game Master and use PC Picture Mode. Update: I am using Game Mode now with some tweaks, see below Update #2
  11. A 3000 series nvidia or 6000 amd graphics card or above with a 2.1 hdmi cable is the best setup possible to avoid any limitation. I run my games on 2060 super (not hdmi 2.1 capable) at 4k 60Hz or 1440p 120 Hz with TCL DLG and everything works fine after following the steps above.
  12. I have seen posts that Windows 11 is better for HDR but still needs work, I am on windows 10 and turn HDR on just for playing HDR games.

Update: I started games in PC picture mode and colors pop more, colors are more saturated and I still have the game bar with HGiG (and I can turn it on or off when in HDR) - when off it enables Dynamic Tone Mapping. Not sure if there is a way to disable both. With PC mode I have VRR and ALLM so latency is not an issue. The only thing I am missing in PC picture mode is the option for 1440p 120hz with DLG so if that is important you must stick to Game Mode. I am hoping I can get an HDM 2.1 cable and a compatible graphics card to test again both Game Mode and PC Picture mode

Update #2: Understanding things better - PC Picture mode uses Native Color Space and has more Color Saturation (60) by default, this is why it looks better. With both the PS4 and Switch I set them to Full RGB on the console and Auto Color Space as Native is too saturated, so the Auto Color Space works well in consoles both in SDR and HDR. Now the thing is that with PC things are different, I am using Native color space for both SDR and HDR and bumping color saturation to 57-58 and 65 respectively to get a punchier picture and I am very happy with the results. All gaming on Gamma 2.2 (0 value)

Update #3 noticed DLG option has less clarity than using the 1440p 4k upscaled resolution (60Hz) PC picture but all in all from 10 ft (3m) away it looks great still
PC picture mode = no DLG only 60hz but there is a 2560x1440 upscaled to 4K that has better clarity than DLG 120hz mode but only 60Hz - PC mode has chroma subsampling for better text but has sharpness tied into it with no option to turn it off (yucks!)

Other settings tips:

Use Color temp -5 for all content types

Movies: backlight from 60 to 18 depending on time of day or preference

Gamma 1 (2.3) for movies in SDR and default (0 - 2.2) for HDR

Sharpening 15 for HDR and 40 for SDR (This is mostly preference I am sitting at 10 SDR and 5 HDR now)

Contrast 90

Judder 2 (also preference sitting at 0 now)

All else default

Use the noise reduction stuff for SDR stuff like TV or SDR content, not for HDR or DV (this is also preference thing, if you are a purist then turn all of that off)

HDR 10: Backlight (100)

Contrast 100

Micro dimming on Low

Gaming: backlight from 40 to 70 depending on time of day or preference for SDR, 100 HDR

Gamma 0 (2.2) for both SDR and HDR

Sharpening 15 (preference, I now use 5)

Contrast 90 SDR and 100 HDR

Color Saturation 57-58 SDR and 65 HDR for Gaming and Default 50 for Movies on both HDR and SDR

All else default and noise reduction stuff/Local Contrast etc off except Micro dimming on low for HDR

It is a nice TV, difficult to not get good picture quality with few teaks