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Old 13th December 2021, 08:59   #62481  |  Link
huhn
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bt 1886 is 2.4.
bt 1886 only changes to a lower gamma on displays that aren't OLED so you can not really change the source depending on that the file it self is not bt 1886 because it can't be. calibrating to bt 1886 is a different story and currently seen as the spec.

and the talk about 2.2 yes it used all the time (or was) to master a movie under studio lights and if that has been done you are "supposed" to use 2.4 in a dark room that's where 2.4 even comes from bt709 is 2.22.
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Old 13th December 2021, 11:26   #62482  |  Link
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i've always found that BT1886 is closer to 2.2 on my TV but that's probably just my TV.
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Old 13th December 2021, 13:05   #62483  |  Link
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Quote:
Originally Posted by huhn View Post
bt 1886 is 2.4.
bt 1886 only changes to a lower gamma on displays that aren't OLED so you can not really change the source depending on that the file it self is not bt 1886 because it can't be. calibrating to bt 1886 is a different story and currently seen as the spec.

and the talk about 2.2 yes it used all the time (or was) to master a movie under studio lights and if that has been done you are "supposed" to use 2.4 in a dark room that's where 2.4 even comes from bt709 is 2.22.
No, BT1886 isn't 2.4 power gamma.

BT1886 takes into account the black floor to compensate. Power 2.4 is flat, BT1886 is only equal to power gamma 2.4 if black is black (0nits). Otherwise is gradually goes from 2.2 up to 2.4, and the targets are calculated taking the black floor into account.
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Old 13th December 2021, 16:21   #62484  |  Link
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Does anyone actually use BT.1886 gamma with an LCD device without local dimming for mere media consumer use case? Sure it prevents black crush ~entirely, but apparently at the cost of distorting of dark shades and killing average scene contrast. I can't imagine that any film maker would describe this as intended viewing conditions.
Also the help text below the 3D LUT section in DisplayCal describes both rel. gamma 2.2 - 2.4 and BT.1886 as correct for rec709 content. So I suspect BT.1886 is correct rather from a theoretical point of view, but in practice not really when it comes to consumer use cases (apart from OLED).
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Old 13th December 2021, 17:35   #62485  |  Link
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Personally I calibrate two SDR modes on my OLED. Working on it right now in fact. Expert bright for regular TV watching at gamma 2.2 100 nits. (Yes, I know, that's not really "bright"....I've been informed already but I like it dark in here relatively speaking even during the day). And Expert dark for movie viewing at gamma 2.4 100 nits. On OLED bt.1886 and gamma 2.4 SHOULD, theoretically be identical more or less. So why not just calibrate for 2.4 and call it a day in that case? I'm still not clear on how a studio could master to bt.1886 anyway given that it's theoretically "dynamic" on where the black floor is. How does that work for content mastering where you should want it to be quite clear what it's mastered to??
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Old 13th December 2021, 17:36   #62486  |  Link
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bt1886 is a compromise made for LCDs. 2.4pure power is the studio standard.

Mastering sdr at 2.2 depends on the delivery target, if it's pc games internet, usually 2.2

Major studio movies were usually by the book 2.4, but because different targets increased over time, they've put out special grades for each.
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Old 13th December 2021, 18:03   #62487  |  Link
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My impression is PC games are mostly 2.4, though of course there are examples pointing the other way or having terrible clipping also with 2.2 due to bad tone mapping/lack of indirect light etc.
Also seems distinction between relative and absolute gamma once again is rather theoretical? At least I don't see any difference with 3D LUTs created accordingly.
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Old 13th December 2021, 18:18   #62488  |  Link
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There really isn't SUPPOSED to be differences. LOL
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Old 13th December 2021, 18:56   #62489  |  Link
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PC games are typically NOT graded to ANY-Standard.

If it looks good to you, you're done.


Movies on the other hand are stricter.
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Old 13th December 2021, 18:59   #62490  |  Link
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Quote:
Originally Posted by SamuriHL View Post
There really isn't SUPPOSED to be differences. LOL
They wouldn't need colorimetry if there was no difference.

It's ok to say there's no "Correct" Gamma. So, 2.2/2.4 are equally correct.

However, there is a "preferred" pipeline. 2.4pure

Bt1886 looks like trash in the majority of cases, so just ignore it.
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Old 13th December 2021, 20:50   #62491  |  Link
huhn
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Quote:
Originally Posted by Manni View Post
No, BT1886 isn't 2.4 power gamma.

BT1886 takes into account the black floor to compensate. Power 2.4 is flat, BT1886 is only equal to power gamma 2.4 if black is black (0nits). Otherwise is gradually goes from 2.2 up to 2.4, and the targets are calculated taking the black floor into account.
and how do you save that on a file?

if you master for bt 1886 you master for 2.4 because you have a 0 black on a high end mastering display. they may aim for bt 1886 but they don't master at it well they do by using 2.4 kind of.

it can be lower than 2.2 not that it matters here. easily looking really really bad.

what so ever the new gamma spec is bt 1886 and you are supposed to use it with new masters.
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Old 14th December 2021, 01:56   #62492  |  Link
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there will be no more update of madvr? there is a better render actually?

Last edited by djsolidsnake86; 14th December 2021 at 02:07.
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Old 14th December 2021, 02:44   #62493  |  Link
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When you say no more update, it depends on what you're looking for. Right now madvr is being updated periodically with improvements to HDR tone mapping. Other than that, no, there's no updates.

As for "better" renderer, that's highly subjective.
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Old 14th December 2021, 03:09   #62494  |  Link
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Originally Posted by SamuriHL View Post
When you say no more update, it depends on what you're looking for. Right now madvr is being updated periodically with improvements to HDR tone mapping. Other than that, no, there's no updates.

As for "better" renderer, that's highly subjective.
last update is from 2019
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Old 14th December 2021, 03:11   #62495  |  Link
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Quote:
Originally Posted by djsolidsnake86 View Post
last update is from 2019
https://www.avsforum.com/threads/the...#post-60645444
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Old 14th December 2021, 06:08   #62496  |  Link
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Quote:
Originally Posted by SamuriHL View Post
There really isn't SUPPOSED to be differences. LOL
Naaah.. .
Quote:
Originally Posted by aufkrawall View Post
Also seems distinction between relative and absolute gamma once again is rather theoretical? At least I don't see any difference with 3D LUTs created accordingly.
What's your black level? See point B.5.a. here.
You can also fake black level in DisplayCal on calibration tab to see this in a greater effect.
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Old 14th December 2021, 15:40   #62497  |  Link
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Quote:
Originally Posted by djsolidsnake86 View Post
last update is from 2019
Last update is from Oct 1, 2021

https://www.avsforum.com/threads/imp...#post-61067550
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Old 14th December 2021, 17:05   #62498  |  Link
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Why is he not posting updates here then?
I thought madVR was long ago abandoned.
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Old 14th December 2021, 19:10   #62499  |  Link
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He decided to work on HDR tone mapping quite a few years ago (at this point) and was involved in the AVS forum thread. Then the Envy happened which has taken the majority of his time and focus. He's continuing to update the AVS forum with new HDR tone mapping beta builds in an effort to improve quality for the Envy and to give the madvr community access to newer builds. But for the most part, they are ONLY focused on HDR tone mapping and do not include anything else. Whether or not that changes after HDR tone mapping is "complete" is anyone's guess.
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Old 14th December 2021, 20:59   #62500  |  Link
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Regarding the 2.4 gamma debate, the reality is that gamma was poorly standardised as the Bt.1886 standard didn't even exist until 2011 and lots of content was made before that.

Before 2011 the convention seemed to be just a 2.4 power law -- although it was never officially standardised -- but different room lighting conditions can call for a different gamma to get the same looking image (eg. 2.2 for daylit room) due to a visual effect called simultaneous contrast.

Sources:
https://www.itu.int/dms_pubrec/itu-r...3-I!!PDF-E.pdf
https://drive.google.com/file/d/1Ot_...Y_uflNQQf/view
https://app.spectracal.com/Documents...0_2.2or2.4.pdf
http://poynton.ca/PDFs/GammaFAQ.pdf

Here I've plotted Bt.1886 with 120nits white and 0.05nits black which produces a curve similar to sRGB. https://drive.google.com/open?id=1MI...rs4S89Vgy1t2Y4



So if a movie was mastered on the above bt.1886 curve then it will look wrong on a 2.4 power law monitor, and vice versa.

For a good balance I target 2.4 power law but with black raised to make 1% or 2% grey visible. Then for daytime viewing I'll shift the whole curve down to 2.2. I wrote an app called Calibration Tools which can do this automatically and gradually during the twilight period according to your GPS coordinates. But it's still not a great solution as ambient lighting isn't consistent due to unpredictable cloud cover causing different room lighting on different days. A proper solution needs an ambient light sensor, however updating the video card gamma table regularly with new values can cause dropped frames which would happen every time ambient light changed.

Last edited by flossy_cake; 14th December 2021 at 21:04.
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