LG OLED Service Menu White Balance: why 192? - AVS Forum | Home Theater Discussions And Reviews
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post #1 of 7 Old 09-04-2019, 06:47 AM - Thread Starter
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LG OLED Service Menu White Balance: why 192?

I was talking with some LG owners of different manufacturing years TV and they were all talking about Service Menu White Balance. So I found the 2016 OLED manual (the latest where that aspect is threatened) and I’ve read how LG do SM WB. They suggest to their technical repair services to display a 216,216,216 (which is 80% luminance in 16-235 patch scale) and set R, G, B value all to 192 and then, while keeping one of them at 192, decreasing the other two until they reach the target. The RGB scale in SM is 0-255, so why 192 and not 233? The only calculation that gave me 192 (almost) is if I convert 204 (which is 80% luminance 0-255 patch scale) in 16-235 patch scale: 191,2. I don’t thing LG is unwillingly keeping their TVs at 75% of their real power. So I’d like to know if someone of you might explain why 192. Of course LG engineers are more than welcome @nezil
Thank you!
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post #2 of 7 Old 09-05-2019, 03:44 AM
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Quote:
Originally Posted by Anger.miki View Post
I was talking with some LG owners of different manufacturing years TV and they were all talking about Service Menu White Balance. So I found the 2016 OLED manual (the latest where that aspect is threatened) and I’ve read how LG do SM WB. They suggest to their technical repair services to display a 216,216,216 (which is 80% luminance in 16-235 patch scale) and set R, G, B value all to 192 and then, while keeping one of them at 192, decreasing the other two until they reach the target. The RGB scale in SM is 0-255, so why 192 and not 233? The only calculation that gave me 192 (almost) is if I convert 204 (which is 80% luminance 0-255 patch scale) in 16-235 patch scale: 191,2. I don’t thing LG is unwillingly keeping their TVs at 75% of their real power. So I’d like to know if someone of you might explain why 192. Of course LG engineers are more than welcome @nezil

Thank you!


For everyone who wants to try this attempt I can say that it's not working. When you set all values to 255 in the service menu then you reduce the gamut.



So stick with the standard value for red 192 and reduce green and blue.

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post #3 of 7 Old 09-05-2019, 04:24 AM
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If you set all to 192 you will get panel native white point and full panel dynamic range.

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post #4 of 7 Old 09-05-2019, 04:54 AM - Thread Starter
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Thanks Tyler, do you also know the reason why it’s 192 and not 233 or 235 or whatever?

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post #5 of 7 Old 09-05-2019, 07:18 AM
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Quote:
Originally Posted by Anger.miki View Post
Thanks Tyler, do you also know the reason why it’s 192 and not 233 or 235 or whatever?


Honestly I have no idea because I don’t know where it actually is in the video path. Modern TVs have a very complex video pipeline where they convert between limited, full Range, YCbCr, RGB, And even go through GPU shaders.
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post #6 of 7 Old 09-06-2019, 06:46 AM
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Quote:
Originally Posted by Anger.miki View Post
I was talking with some LG owners of different manufacturing years TV and they were all talking about Service Menu White Balance. So I found the 2016 OLED manual (the latest where that aspect is threatened) and I’ve read how LG do SM WB. They suggest to their technical repair services to display a 216,216,216 (which is 80% luminance in 16-235 patch scale) and set R, G, B value all to 192 and then, while keeping one of them at 192, decreasing the other two until they reach the target. The RGB scale in SM is 0-255, so why 192 and not 233? The only calculation that gave me 192 (almost) is if I convert 204 (which is 80% luminance 0-255 patch scale) in 16-235 patch scale: 191,2. I don’t thing LG is unwillingly keeping their TVs at 75% of their real power. So I’d like to know if someone of you might explain why 192. Of course LG engineers are more than welcome @nezil
Thank you!
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Thanks Tyler, do you also know the reason why it’s 192 and not 233 or 235 or whatever?
I believe this is happening mainly for historical reasons...

All these instructions for service manuals is for some procedures to repair the TVs, in case a panel will be replaced (in that case they calibrate the WB values according to the manual procedure) or when a Main Board will be replaced, in that case they only copy-paste the old M/B values to the new M/B values.

These instructions are a copy-paste mainly of procedure performed from LCD years, when there were no HDR available or people worried so much about a panel output levels. A lot of display controls are still using old 'historical' names, like IRE which coming from analog signal world (analog signal input) but still LG name like that the Grayscale steps in a complete digital world.

Or the fact that displays are still using gamma based loaded characteristics, while the actual panel is linear, just it will require a lot of re-design of whole processing (for not following 'historical' stuff), companies have to perform changes to manufacturing process etc.... for panels to have selectable native gamma or native PQ output/processing or linear response.

So 192.192.192 values was for 80% Gray..... it was a good value to provide a typical/fast 1-Point RGB balance fix, since for gamma based grayscale, if the panel has 400 nits output with OLED Light 100, then 80% Grayscale target Y will be 233 nits (for gamma 2.4), so its closer to the center of the total luminance level, doing one calibration at 80%, it should better handle whole grayscale, than from focusing to 100% White calibration only.

As most users of LG may seen, while their display has 2-Point RGB balance @ Service Menu WB menu, always only the RGB-Gain values are adjusted from the factory, they use always the RGB Cuts untouched (64.64.64), this speeds up the procedure since if they were touching the RGB-Cuts, this should affect the RGB-Gains also, so repair guys should have spend more time to handle both controls, so to measure whole grayscale etc....performing more an actual calibration than only a single repair.
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post #7 of 7 Old 09-06-2019, 06:53 AM
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Originally Posted by BlackJoker View Post
For everyone who wants to try this attempt I can say that it's not working. When you set all values to 255 in the service menu then you reduce the gamut.

So stick with the standard value for red 192 and reduce green and blue.
I will describe the procedure for someone may interested to find out...

The only way to find out, is to upload a UNITY 1D LUT with DeviceControl and the measure the display with Quick Profile of Primary only (which will measure 21-Point Grayscale and 20-Point Luminance of R,G,B with 100% Saturation).

The 'reference measured data', RGB balance, clip, RGB separation, gamma, we will keep these data as the reference values for full panel dynamic range performance, since uploading 1D LUT it should bypassed WB SM adjustments.

Then reseting the TV to be uploaded the 1D LUT Unity and using 192.192.192 values for the start, measure again with Quick Profile of Primary and then compare with the previously 'reference measured data'.

If its not the same, then should be tested different values, like 195.195.195. or 200.200.000 until there will be the exact match with UNITY 1D LUT.

Using that method we will find out what is the correct full dynamic range values.

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