RGB clipping for no discernible reason

923 Views 8 Replies 3 Participants Last post by aaroncledge, Aug 10, 2019

aaroncledge

Discussion Starter · Aug 10, 2019

Hi all,

I just got an LG OLED, and I was trying to set it up. I ran the AVS calibration tests for black and white clipping on the internal LG video player. Every thing went as expected. I was able to see every line, and then adjust the brightness and contrast.

I then tried to do the same with my HTPC. (A run-of-the-mill Windows PC with a GTX 1050 ti). I understand the basics of RGB Level Ranges, and I don't think this is a case of me just being stupid. (Although, if it is, please correct me and I'll be so happy). I use Kodi, and I followed the suggested Limited-Full-Limited settings in their wiki.

When those settings didn't work, I tried everything else, systematically switching though all conceivable combinations of RGB settings in the player, the graphics card, and the TV. None of them showed lines below 17. The same issue occurred with the the brightness.

In case Kodi was the culprit, I also tried playing the video in Windows Media Player but was still unable to see the lower values.

In addition to clipping the values, the image coming out of my HTPC seems to be significantly darker than the LG internal player. I could see 17 flashing at a brightness of 39 on the internal player, but I had to crank it up to 60 to see it on the HTPC.

It really feel like there is some hidden setting that I'm missing, either in the TV or in Windows or in the Nvidia control panel. I would really appreciate it if anyone has any ideas.

Thanks.

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Onkyoman

· #2 · Aug 10, 2019

If you are using a PC input for the PC, try changing it to one of the video modes instead.

A HTPC typically works best with a chain of RGB (0-255) Full -> Full -> Full.

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Foxbat121

· #3 · Aug 10, 2019

you must match video levels between PC and TV. TVs are typically default to video or limited range level while PCs are typically default to PC or full range level. If you have a mismatch, you get either foggy picture or clipping. Such mismatch can't be calibrated away.

On LG TV, typically you need to set your HDMI input to PC label to switch that input to PC level.

On PC side, you need to configure each video player to match the correct level. There is no system wide setting. The Limited/full range setting on video card should be avoided if possible.

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aaroncledge

Discussion Starter · #4 · Aug 10, 2019

Onkyoman said:
If you are using a PC input for the PC, try changing it to one of the video modes instead.

A HTPC typically works best with a chain of RGB (0-255) Full -> Full -> Full.

Thanks for the ideas. Although I didn't mention it in my first post, I did tried changing the name of the input to something other than "PC." It made no difference.

As I mentioned, I tried every possible combination, including "Full-full-full." It did not fix the problem.

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Foxbat121

· #5 · Aug 10, 2019

Clipping happens when your TV is set to video/limited range while your PC is outputting PC levels. Your TV was expecting 16 as black and 235 as white while your PC is outputting 0 as black and 255 as white. Don't use calibration tool to adjust your TV if you are not sure if the levels are matched first. That will make thing worse.

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aaroncledge

Discussion Starter · #6 · Aug 10, 2019 (Edited)

Foxbat121 said:
you must match video levels between PC and TV. TVs are typically default to video or limited range level while PCs are typically default to PC or full range level. If you have a mismatch, you get either foggy picture or clipping. Such mismatch can't be calibrated away.
...
On PC side, you need to configure each video player to match the correct level. There is no system wide setting. The Limited/full range setting on video card should be avoided if possible.

Thanks for reply. As I mentioned before, I tried every possible combination of of full and limited RGB ranges (on the TV, the video card, and the video player), just to make 1000% sure that a mismatch wasn't the problem.

Foxbat121 said:
On LG TV, typically you need to set your HDMI input to PC label to switch that input to PC level.

On my TV, the "PC" input setting seems to be little more than a label. I do have it set to PC currently. There is a "Black Level" setting on the TV ("Auto," "Low," or "High"), which I believe is the LG setting for switching between limited and full. I tried it on both "low" and "high" as part of my 1000% test. It had a major impact on the image (the kind of response I would expect from a switch between limited and full range) but neither setting worked properly.

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Foxbat121

· #7 · Aug 10, 2019 (Edited)

I would reset the LG settings to default and try again. It seems that you are not getting the correct PC levels. I don't remember which Black Level settings I used before on my old LG OLED. It is probably best to ask your TV's owner's thread for it. But with levels matched, you don't need to do much calibration on black levels. In the PC label setting, it disables all the video processing as well as over scan of the TV.

Leave the graphic card setting to full range. Adjust your player to output the correct range. If you can't switch your TV to full range, try switch your player to output limited range instead. With this setting, you will still see clipping on desktop and other software but at least the video play back will be in correct level.

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aaroncledge

Discussion Starter · #8 · Aug 10, 2019

I tried a factory reset and setting it up again. It was worth a try, but didn't fix anything.

Our TVs are clearly quite different, because there is no overscan on any of the input settings on my set. Unfortunately, my TV is a Korean model, and I couldn't find a thread about it.

I'm aware that when the levels are properly matched, the black levels don't need big adjustments. This is not my first HTPC setup, and I remember a few times when Windows updates and graphics card updates changed the computer's setting. It's a big difference. I know what it looks like when it's wrong.

I couldn't post this earlier, because I didn't have link posting privileges, but this is the wiki page I mentioned. https://kodi.wiki/view/Video_levels_and_color_space I tried all 8 possible combinations listed there (switching Nvidia Control Panel from "Full" to "Limited," the LG "Black Level" from "Low" to "High," and ticking and unticking the Kodi option to "Use Limited Color Range (16-235)"). Obviously some settings looked better than others, but none of them displayed the full, proper image.

With the current settings I'm using, it's as close to "right" as possible, but it's still not correct. Of course, multiple settings mismatches can amplify the problem and make it look worse and worse. But even with the best settings I've found, it seems like there's something else wrong in the pipeline.

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aaroncledge

Discussion Starter · #9 · Aug 10, 2019

The problem seems to be solved. I updated my Nvidia driver. Wish I thought of that sooner. Thanks again for your input.

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