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Display Calibration Light Illusion Forums / Display Calibration /

LG Series 7 (and possibly series 6) HDR TVs (and now Panasonic DX900 & Sony Z9D too!)...

Author Steve
Scene
#1 | Posted: 6 Apr 2017 09:53 | Edited by: Steve 
I've been discussing HDR calibration with Bram at FSI, specifically consumer displays...

The big issue is that consumer TVs cannot be accurately HDR calibrated, due to a combination of limited internal CMS capabilities, and the 'burnt-in' EOTF, with roll-off.

But, FSI (Bram) seems to found a bit of an exception...

On LG OLED TVs you can use the service remote to manually force the display into 'HDR On' mode from the service menu.

FSI have only been able to do a short test on the newer LG C7 OLED, but this may work on the 6 series OLEDs as well?

When you do this (at least on the C7) the display goes to its true peak luminance output without requiring HDR metadata over the HDM connection and without triggering a ST2084 EOTF. The upshot of this is that because that HDR metadata is not present the display doesn't apply the PQ EOTF. So you get 700~800 nits output with an EOTF that is much closer to a power curve than it is a PQ type response.

Due to being short on time FSI were not able to do a large profile + 3D LUT calibration, but did do a quick profile (grey only) and exported just a 1D LUT targeting ST2084 clipping at 675 nits. It generated a response pretty close to targeted PQ EOTF with just that very rough test, as follows.

Piccy

This quick test does suggest there could be a very workable way of using the LG OLED TVs + a BoxIO LUT Box for HDR/4K calibration... with accurate EOTF and colour calibration.

And further tests by LightSpace CMS user Pepijn Klijs suggests the Panasonic DX900 can be treated the same, as can the Sony Z9D - and it may be true of other TVs too...

Basically, if you can disable the in-built/burnt-in EOTF, but maintain the backlight running in HDR mode brightness mode, then you can use an external LUT Box, such as the BoxIO, to calibrate the display using LightSpace CMS - to ANY of the HDR standards within LightSpace.

ST2084 (all PQ based HDR standards)
BBC/NHK HLG
Philips/Technicolor HDR
EclairColor HDR

(The only issue I can see with the DX900 is it seems to have a horrendously 'blue' backlight, making the backs appear very blue... The Sony Z9D we have not yet evaluated.)

Steve

Author Steve
Scene
#2 | Posted: 12 Sep 2017 09:45 | Edited by: Steve 
An update on the LG TVs:
(But the WARNING applies to the other TVs too!)

Using the remote to turn off the HDR EOTF is very dangerous, as it is possible to cause major damage to the TV...

However, if you do use this mode, setting 'HDR Enable to On' the EOTF essentially becomes a standard power law gamma function (e.g. 2.2).

This means you will not see a PQ type EOTF with clipping instead of a roll off - you just get a very bright TV with standard gamma response.
(This power law gamma works for HDR calibration, but is pointed out for clarification, as some people expect to see a PQ EOTF with clipping rather than tone mapping/roll-off in this mode, and that isn't the case.)

Without 'HDR Enable set to Off' the TV will max out at about 400 nits, basically acting as an SDR TV.
With 'HDR Enable set to On' the display will typically see 600 to 750 nits peak luminance.

But, be warned, while there is no issue at SDR levels, at HDR levels there are real potential issues with image burn-in.
So small test patches (L20 for example) are suggested, and should be maintained on-screen for very short periods of time!.
The issue is that at HDR levels burn-in happens very, very fast - you have been warned!

It is therefore not suggested users do anything beyond short profile sequences (Quick Profiles?) because any long profile will likely damage the TV.
Even too many Quick Profiles with small patches can be problematic - and cause irreversible burn-in.
(There is no way around this as it is not peak values that are the issue - any patch above a nominal SDR 100 nits can actually cause issues!)

When playing back real HDR footage there is little issue as the, image changes quickly, with little time spend on static high luma scenes, as happens with any form of calibration.

That does make HDR calibration a real problem, and in reality there is no way to accurately calibrate these TVs for professional HDR use.
For SDR they can be very accurate.

You have been warned!

Steve

Author mhsmith
Mono
#3 | Posted: 25 Sep 2018 11:37 
We've just successfully used this method to calibrate a LGC7 For HDR using a quick profile (greyscale).

I was wondering if using the new "Stabilisation" feature with a black patch for .5 seconds would prevent burn in on larger patch sequences?

We're using the minimum patch size possible.

Author Steve
Scene
#4 | Posted: 25 Sep 2018 11:40 
Yes, that could help.
I would use a Stabilising patch and a Drift patch to try to counter image burn-in.

Steve

Display Calibration Light Illusion Forums / Display Calibration / LG Series 7 (and possibly series 6) HDR TVs (and now Panasonic DX900 & Sony Z9D too!)... Top
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