Originally Posted by sorinelionut
A calibrator who wants to teach you, will tell you so, when you calibrate 2p or 20p you never go to toch the green. The reason is that once adjusted the green, you will get out of gamma.
Yes, that's the basic rule of thumb. However, it's not universally true. There are other examples beyond LG OLEDs where the digital-analog mapping is first aligned to peak Red rather than peak Green (again, 2p Gain).
If you take a look at the factory values in the EZ-ADJUST menu you will find that Red Gain
is set to it's digitally nautral peak value and D65 (in case of Warm) is set by adjusting (decreasing) the Green and Blue Gain
values. I am not sure if this has changed since I experimented with this on a C7 (*) but increasing Red Gain in either the EZ-ADJUST or
the normal user menu from it's default (192 and 0 accordingly) immediately resulted in clipping at the high end of the Red gradient. You might not notice this in SDR mode where the default Contrast=85 setting allows for "whiter-than-white" shades, so this clipping starts in that normally not measured/seen contrast region (between the 236-255 8bit values or 100-109% if you like) but I would still consider it a bad practice to distort the WTW range when it's not necessary and the elegant solution is easy to figure out. But more importantly, HDR mode is different, it doesn't allow for whiter-than-white with Contrast=100 (the device tries to reach it's absolute peak luminance, so it doesn't waste any potential contrast range to potentially display "invalid" values).
* Now, also keep in mind that more "thoughtful" manufacturers often re-scale the values, so that no matter what you set, the highest number (after all potential factory and user offsets are applied to it) is set to it's digitally neutral peak value and the rest if ofseted accordingly. So, for example, if the device starts from 192,165,125 where 192 is the peak and the user increases Red in the user menu by +10, the effective values become 192,155,115 (automatically on-the-fly) to avoid clipping (banding on the upper end of the contrast range) or unnecessary waste of available brightness (limited peak lumininance if you were to apply negative offsets to all, like -10 -12 -8 to R,G,B in the user menu).
Panasonic used to do this on their plasma TVs. You simply couldn't cause clipping or brightness reduction. The values in the service menu were immediately re-scaled and saved during the adjustment and the user-menu offsets were similarly scaled in the background (however those were not saved as re-scaled but left as the user pleased in order not to confuse the user). And yes, these were always aligned to Green (hence "don't touch green!" would have applied, except it didn't matter at all, errors were auto-corrected).
The last few Samsung PDPs were different. Those were aligned to Red, very similar to these LG OLEDs (if I recall their neutral value is also 192 but I haven't touched those in years, so I could be wrong but it's definitely Red aligned).
So, when things are alligned to Green and there is no auto-magic re-scaleing then yes, adjusting Green could distort gamma (since the tone response adjustment was made to fit the entire un-clipped/unlimited contrast range). But the same goes for Red if that's what the factory values were aligned for. (However, yet again, sometimes every potential error is automatically taken care of in the background or it remains insignificant due to things like whiter-than-white, etc). Often times you can tell you f'cked it up if you have to reduce the factory default Contrast value (hence doing the aforementioned "re-scaling" manually in a crude way). But most won't care and do it anyways (and it usually doesn't matter, so they get away with it just fine).
Of course the 20p is different. The proper "rule of thumb" there is : never touch the highest point (if it's 100% since you already set that with the Gains in 2p --- unless the user menu already hides the 100% point [some do since it's completely redundant but most don't care to be logical and pretty but allow you to play dirty]). And yes, green affects the gamma the most but it's not exactly true that green=gamma (it just happens to appear like that due to the circumstances when you play with ~6500K where green is the brightest).
Don't be a Flat Erather.
Don't trust but do verify...