Another BT.1886 vs. Power gamma question - Page 2 - AVS Forum | Home Theater Discussions And Reviews
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post #31 of 40 Old 03-27-2019, 09:08 AM - Thread Starter
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Bruce2019,

Thanks for the feedback. I see that I am a bit bright at 10IRE and 20IRE so clearly not crushing, if anything a bit too bright is what you are saying? Assuming a power 2.3 target.

My 10 and 20 IRE cuts are at minimum for some colors so guess I have to live with that miss there. Having tried various overall cut/gain/TV gamma settings, this is the best balance of grayscale and luminance accuracy at the low end getting me to this result of around 1.5 or under from 10IRE to 20IRE.

This does remind me of one nagging question. We are talking about black levels etc but the chart we are looking at (vs. what I am seeing when I am watching the display) has 0 IRE significantly different than when I am watching the display as 0 IRE with dimming off is much darker (viewing) than with on (calibrating). The chart is starting at .7 cd/m2 ish while my set with dimming off is around .05 or .06 cd/m2.

I understand dimming needs to be off so gamma is stable, but wonder what it means to the dark end of the gamma results? Or is it irrelevant due to the fact that by definition, it impacts zero IRE?

Looking forward to the fun of using my HDFury Linker for my first HDR10 calibration next!

Thanks,
BJBBJB

There are several very knowledgeable contributors on this thread that I have learned a lot from over the years reading their posts.

Do any have input on my questions above? And in particular, understanding the low-end measurements as it relates to gamma targets set with local dimming appropriately being off during calibration.

Thanks,
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post #32 of 40 Old 03-28-2019, 08:08 AM
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Originally Posted by BJBBJB View Post
Most reviews show that display measures around .05 cd/m2 with FALD on. Ironically if I use that as my input black point for BT.1886 the curve is not too far off from my 2.3 power gamma. In the future should I just use the displays true black point with FALD on as my BT.1886 target for calibrating with FALD off? I know my BT.1886 with measured black point assumed my set did not get that black and set the curve accordingly. And it had me push luminance in calibration to match.
Hi, when you are measuring your black, since you have an led/lcd based back-light display, which completely dim off when it will see black patch, your contrast ratio it will be infinitive and not represent the real contrast ratio of the display, while the 0 nits black you will receive (from meter error reading) it will provide wrong calculation for your gamma later.

For that reason you need to keep the display back light active, you can press the Info button of your display remote when you will measure your black, to display something to your screen (HDMI info etc...) to keep the backlight active, during the black measurement.

If you have my calibration disk, you can pause the pattern when you will see the 'pattern info announcement text'', located to the right centered area of the screen, so to measure that time your black: https://www.avsforum.com/forum/139-d...l#post56281026

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post #33 of 40 Old 03-28-2019, 10:21 AM
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Quote:
Originally Posted by ConnecTEDDD View Post
Hi, when you are measuring your black, since you have an led/lcd based back-light display, which completely dim off when it will see black patch, your contrast ratio it will be infinitive and not represent the real contrast ratio of the display, while the 0 nits black you will receive (from meter error reading) it will provide wrong calculation for your gamma later.

For that reason you need to keep the display back light active, you can press the Info button of your display remote when you will measure your black, to display something to your screen (HDMI info etc...) to keep the backlight active, during the black measurement.

If you have my calibration disk, you can pause the pattern when you will see the 'pattern info announcement text'', located to the right centered area of the screen, so to measure that time your black: https://www.avsforum.com/forum/139-d...l#post56281026
For my set, in trying to use BT-1886, I've thought about turning FALD off for my black reading, and back on for the rest. I wonder if it makes sense as an approach.
With FALD on, my meter reads 0 nits at black making BT.1886 curve just power curve.

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post #34 of 40 Old 03-30-2019, 09:50 AM - Thread Starter
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Quote:
Originally Posted by ConnecTEDDD View Post
Hi, when you are measuring your black, since you have an led/lcd based back-light display, which completely dim off when it will see black patch, your contrast ratio it will be infinitive and not represent the real contrast ratio of the display, while the 0 nits black you will receive (from meter error reading) it will provide wrong calculation for your gamma later.

For that reason you need to keep the display back light active, you can press the Info button of your display remote when you will measure your black, to display something to your screen (HDMI info etc...) to keep the backlight active, during the black measurement.

If you have my calibration disk, you can pause thte pattern when you will see the 'pattern info announcement text'', located to the right centered area of the screen, so to measure that time your black: https://www.avsforum.com/forum/139-d...l#post56281026
Ted,
Thanks! Makes perfect sense. That is probably how the reviewers measured it.

With my DVDO TPG there might be some border around the 18% that might also trigger this? I may also find your disc which I did utilize before I had a generator.

Would it then be appropriate to use that value as an input 0IRE vs. measured value for either BT.1886 or power gamma?
I do not plan on re-calibrating my SDR calibration, But will be doing an HDR10 calibration on this set at some point.So it might make sense there?

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post #35 of 40 Old 04-03-2019, 05:44 AM
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Originally Posted by BJBBJB View Post
Ted,
Thanks! Makes perfect sense. That is probably how the reviewers measured it.

With my DVDO TPG there might be some border around the 18% that might also trigger this? I may also find your disc which I did utilize before I had a generator.

Would it then be appropriate to use that value as an input 0IRE vs. measured value for either BT.1886 or power gamma?
I do not plan on re-calibrating my SDR calibration, But will be doing an HDR10 calibration on this set at some point.So it might make sense there?
Hi, you will need to get a proper black level measurement for SDR calibration only, since the gamma will be calculated based to your black/white measurements as reference. (relative targets)

For HDR10, there specific luminance values per digital bit, so it doesn't matter if you have 0 or 0.1 black level, the target luminance per each 10-bit digital levels are fixed, they are absolute targets.

See for example CalMAN 5 calculated 64-Point Grayscale luminance targets for ST.2084, based as example to Samsung UE55KS9000 measurement data (Black Level 0.039 nits - Peak White: 1460 nits), some near black will clip:



See there for more info.

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post #36 of 40 Old 04-03-2019, 06:26 PM - Thread Starter
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Quote:
Originally Posted by ConnecTEDDD View Post
Hi, you will need to get a proper black level measurement for SDR calibration only, since the gamma will be calculated based to your black/white measurements as reference. (relative targets)

For HDR10, there specific luminance values per digital bit, so it doesn't matter if you have 0 or 0.1 black level, the target luminance per each 10-bit digital levels are fixed, they are absolute targets.

See for example CalMAN 5 calculated 64-Point Grayscale luminance targets for ST.2084, based as example to Samsung UE55KS9000 measurement data (Black Level 0.039 nits - Peak White: 1460 nits), some near black will clip:



See there for more info.
ConnecTeddd,
Thanks, great info and good to know for my I try my HDR run! No gamma games! And I assume dimming off.

Re-reading your posts above for SDR, it sounds like the best approach is to keep my signal generator runs is to get that 0IRE reading with dimming on, then use that as a manually input black point. Then when using either BT1886 or PG use that value for 0 but then I can turn dimming off to appropriately do a 10 point automated grayscale run with appropriate gamma behavior. Does that make sense?

Although above it was mentioned I might want to take 5 and 10IRE to a slightly higher gamma, my 0 and 20 ire cuts are at about minimum. And on prior runs when I started with a lower overall cut to get me more room, it created issues above 10ire. My DVDO TPG brightness chart shows just some difference from c16,17 etc. Much darker and would fear crush?

Thanks,
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post #37 of 40 Old 04-03-2019, 07:43 PM
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@BJBBJB IRE is the wrong reference to use here. It's a unit of measurement intended for use with the older analog video system and is incorrect for describing digital video levels as used today. Better to use "% Gray" or simply "%". Because it implies a certain input voltage threshold, "IRE" is not exactly the same as "% Gray".
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post #38 of 40 Old 04-04-2019, 05:33 AM - Thread Starter
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Originally Posted by Rolls-Royce View Post
@BJBBJB IRE is the wrong reference to use here. It's a unit of measurement intended for use with the older analog video system and is incorrect for describing digital video levels as used today. Better to use "% Gray" or simply "%". Because it implies a certain input voltage threshold, "IRE" is not exactly the same as "% Gray".
Got it, thanks!
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post #39 of 40 Old 04-11-2019, 12:21 PM
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Originally Posted by ConnecTEDDD View Post
The black level of the display is mapped to Zero and the white level mapped to One, then the gamma curve applied between the two.

Therefor there should never be clipping, regardless of the gamma used.

If the contrast ration of the display is also very low, as the black level is high, that is a separate issue.

But its all related with about how the content is being mastered, if its mastered with 2.4 gamma and based to your BT1886 calibration you will have 2.0 @ 10% Gray for example, then you will be able to see details you should not have to see, so image will look very wash-out, flat and with less depth.

Currently, studios are using Gamma 2.4 ...about 2016 and later.

Before about 2016 it was 2.35

Before about 2014 it was 2.2

If you watch a movie which been released at 2012 @ Blu-Ray, with 2.4 gamma now, it may look a bit dark.

Ideally you need a secondary picture mode calibrated with different gamma, to give you flexibility when you are watching various content (older releases).

When you have zero black (OLED) with BT.1886 then it has the exact same luma targets as Power Law Gamma 2.4

Thankyou for that explanation..


I actually dont have so much of an issue with old content vs new content.. Old DVDs, new Blu rays.. not a real issue..


But with new content: Cable tv vs. Netflix (and the other streaming services) and blu ray..


So basically cable tv vs. Higher quality productions..


Cable tv actually looks best on Gamma 2.0.. is it possible that the tv stations produce it that way because most of the tvs out there are not 2.2 or 2.4 but mostly have a brighter gamma?


And Netflix and Blu ray are professional mastered for "darker" sets.. And it is not imagination.. If a movie is broadcasted over cable tv.. it looks brighter then on Netflix..


To me.. Gamma 2.2 or 2.4 is a massive difference.. 2.4 I can not even use with my plasma tv, because of limited light output..


2.0 and 2.1/2.2 are the 2 gammas I switch around.. But does it really have to be that way? And with gamma 2.0 I mean real 2.0ish gamma, which is the stock setting of many Panasonic Plasma TVs..


But Plasma TV with limited light output is a different kind of story.. That is what I really admire about lcd and oled.. Perfect full screen brightness, no ABL, no gamma tricks..

Panasonic 42inch ST60 owner
Panasonic 42inch S10 ES (Europe/Silver) owner

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post #40 of 40 Old 04-13-2019, 08:01 PM
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abl issues are on oled and hdr led tvs.
pattern size, apl, and on/off settings can have an effect.

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