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-   -   What is BT.1886 gamma? (http://www.avsforum.com/forum/139-display-calibration/1450925-what-bt-1886-gamma.html)

Wouter73 01-10-2013 02:48 AM

Hi,
I read a lot of discussions on gamma, and while I do believe I have a rudimentary understanding of what gamma is and what it means to have a certain number of gamma (2.22,2.3,2.4 and so on), I also read about BT.1886 gamma. But I can't find a clear explanation about what it is? I understand it is some kind of standard, but what does it do exactly?

The reason I ask, is because in autocal I have the option to choose bt1886.

Thanks!

Wouter.

realzven 01-10-2013 03:17 AM

some interresting info in this thread

How power law gamma calibration can lead to crushed blacks

http://www.avsforum.com/t/1409045/how-power-law-gamma-calibration-can-lead-to-crushed-blacks

Light Illusion 01-10-2013 04:50 AM

No DVD/Blu-Ray you will watch will have been mastered to this new standard...
(or general TV programs either...)

It will be adopted in time, but that time is not yet.

Steve

sotti 01-10-2013 10:26 AM

Here is the documentation on BT.1886
http://www.itu.int/dms_pubrec/itu-r/rec/bt/R-REC-BT.1886-0-201103-I!!PDF-E.pdf

The goal of BT.1886 was to create a standard that effectively emulated what CRTs did. The idea being that you could start using the new formula on flat panels replacing the old CRT BVMs. So while it's true it wasn't used officially to master DVDs, the intent is that you'd calibrate a display with BT.1886 and get results comparable to what the old BVMs did. It is accurate to say that while studios are interested, aware, and will likely move to BT.1886 at some point, they aren't currently calibrating their displays with it. Of course that may be partially due to a lack of software with support for BT.1886.

Doug Blackburn 01-10-2013 07:16 PM

Why, exactly, would pro studios want to emulate a dead & far-from-perfect display technology? And why, exactly, would they want to use displays with a gamma that is not supported in consumer video displays and can't be retrofitted to a consumer video display without a professional calibration that maybe 1% of the video display owning public would ever pay for or even understand/know about?

Isn't the whole point to have the video displays used to create consumer video programming (including movie discs) "match" fairly closely, displays consumers have in their homes? (not that consumer displays, in general, are particularly close to any gamma standard out of the box).

sotti 01-10-2013 08:27 PM

Quote:
Originally Posted by Doug Blackburn View Post

Why, exactly, would pro studios want to emulate a dead & far-from-perfect display technology?

Because it is what all the existing content was mastered with.
Quote:
why, exactly, would they want to use displays with a gamma that is not supported in consumer video displays and can't be retrofitted to a consumer video display without a professional calibration that maybe 1% of the video display owning public would ever pay for or even understand/know about?

It would be exactly the same regardless of the specific EOTF they chose.
Quote:
Isn't the whole point to have the video displays used to create consumer video programming (including movie discs) "match" fairly closely, displays consumers have in their homes?

Not really, it's to have a specific exchange format so professionals can guarantee they are all looking at the same thing. It's display manufacturers responsibility to follow the standards, 99% of consumers are just along for the ride.

Doug Blackburn 01-11-2013 11:40 AM

So are you saying they would use 1886 amongst themselves, but when it comes time to release the movie for cinema, they would remaster to digital cinema standards and when it came time to create a master for a Blu-ray release, they would remaster to Rec 709 so the general public would never "see" a release in 1886 in either a theater or at home?

sotti 01-11-2013 12:59 PM

Quote:
Originally Posted by Doug Blackburn View Post

So are you saying they would use 1886 amongst themselves, but when it comes time to release the movie for cinema, they would remaster to digital cinema standards and when it came time to create a master for a Blu-ray release, they would remaster to Rec 709 so the general public would never "see" a release in 1886 in either a theater or at home?

Obviously DCI stuff would be mastered using DCI standards.

Home use Rec.709 "should" all basically be BT.1886, because the standard always was a CRT.
Very few home users calibrate their displays. Even fewer have any control over gamma (10 point+), so most people live with what manufacturers ship out, which isn't something you can account for as very few displays have any kind flat gamma out of the box. Then their are displays that advertise gamma numbers in their menus, but never actually measure at those numbers. Gamma in the wild is a total crap shoot, from anywhere from 1.9-2.5

BT.1886 is a standard in a sea of ambiguity. I've talked to people in post houses and found that even within their own facilities, gamma is inconsistent (ranging from 2.2 to 2.4), much less from post house to post house. The curve you get from Bt.1886 fits nicely in sweet spot for what people have been using, but makes it a hard standard.

Also I don't know what you mean when you say "remaster to rec709", because rec709 doesn't have a gamma function to master too, unless you count BT.1886.

persona 07-03-2014 11:48 AM

have to bump this, In order to have the most natural looking blu-ray picture (which means most faithfull to the source material), what would be the best way to choose? Gamma 2.2, 2.4 or BT.1886?

HDTVChallenged 07-03-2014 11:52 AM

Quote:

Originally Posted by persona (Post 25465714)
have to bump this, In order to have the most natural looking blu-ray picture (which means most faithfull to the source material), what would be the best way to choose? Gamma 2.2, 2.4 or BT.1886?

What display do you have?

sotti 07-03-2014 11:57 AM

Quote:

Originally Posted by persona (Post 25465714)
have to bump this, In order to have the most natural looking blu-ray picture (which means most faithfull to the source material), what would be the best way to choose? Gamma 2.2, 2.4 or BT.1886?

Many people have found BT.1886 to work well for most content. The ideal gamma would be the one used when the content was mastered. Not every movie or show used the same target when it was mastered. So in the end you'll never really know if it's exactly right or not until everyone is done switching to BT.1886.


BT.1886 is a fairly middle ground between 2.2 and 2.4, but it comes out of black a littler faster than either of them, which helps with shadow detail. I personally use BT.1886 and think it looks great.

barleyguy 07-03-2014 12:03 PM

There's a video where Scott W and the head of ISF spend almost an hour talking about BT 1886 and the tangential topics. It's on the home page under "Home Theater Weekly". That's on the off chance you'd rather hear it explained than read about it.

persona 07-03-2014 12:45 PM

Quote:

Originally Posted by HDTVChallenged (Post 25465802)
What display do you have?

Panasonic TX-P50VTW60

I guess it would make sense to have 2 profiles, one with BT.1886 for newer movies and one with a 2.2 Curve for older movies?

sotti 07-03-2014 02:18 PM

Quote:

Originally Posted by persona (Post 25467490)
Panasonic TX-P50VTW60

I guess it would make sense to have 2 profiles, one with BT.1886 for newer movies and one with a 2.2 Curve for older movies?

Unless the older movie was mastered with 2.4, or 2.35 or 2.3. It's not like the standard was 2.2 and then they changed it to BT.1886. There was no standard at all previously, so things where all over the map. BT.1886 is the first standard for display gamma.

So i would say just one profile with BT.1886 is probably is likely all you need.

HDTVChallenged 07-03-2014 10:22 PM

Quote:

Originally Posted by persona (Post 25467490)
Panasonic TX-P50VTW60

I guess it would make sense to have 2 profiles, one with BT.1886 for newer movies and one with a 2.2 Curve for older movies?

Sure. OTOH, on plasmas its often better to just stick with power-law @ ~2.2.

sotti 07-03-2014 10:29 PM

Quote:

Originally Posted by HDTVChallenged (Post 25479890)
Sure. OTOH, on plasmas its often better to just stick with power-law @ ~2.2.

Why?
Plasma's work great with BT.1886.

HDTVChallenged 07-03-2014 10:39 PM

Quote:

Originally Posted by sotti (Post 25479978)
Why?
Plasma's work great with BT.1886.

A lot of plasma owners complain that BT1886 is 'too dark' for their tastes. I assume this is because bt1886 often approaches 2.4 gamma on plasma ... plus the inevitable affects of ABL dimming the peak whites ... Plus the wonky multipoint greyscale adjustments ... MMV of course. :)

chunon 07-05-2014 08:05 AM

6 Attachment(s)
Quote:

Originally Posted by sotti (Post 25479978)
Why?
Plasma's work great with BT.1886.


Joel I have tried BT1886 on my plasma's and don't like it. I prefer 2.3 power law but everyone has different tastes.

hievinhealt 07-05-2014 08:22 AM

great,It's not like the standard was 2.2 and then they changed it to BT.1886. There was no standard at all previously, so things where all over the map. BT.1886 is the first standard for display gamma.thanks [IMG]http://*******/Prn9DS[/IMG]

sillysally 07-05-2014 06:36 PM

Quote:

Originally Posted by sotti (Post 22816426)
<Snip>
The curve you get from Bt.1886 fits nicely in sweet spot for what people have been using, but makes it a hard standard.

Also I don't know what you mean when you say "remaster to rec709", because rec709 doesn't have a gamma function to master too, unless you count BT.1886.

Quote:

Originally Posted by sotti (Post 25479978)
Why?
Plasma's work great with BT.1886.

Yes sotti I agree with you 100%, even using BT 1886 for a plasma. In my case a 65VT60.

I am not going to give a opinion, simply because it doesn't mean anything. Chances are that the folks giving these opinion's have never seen a well calibrated BT 1886.

Click on this link below to see for yourself how well using the BT 1886 2.4 formula can work. Once the file downloads open with your browser (internet explorer, Google, ect.)
http://s000.tinyupload.com/index.php...71250428642221

btw, I understand why some may not appreciate what the BT 1886 can really do. I used to think the same way as some of you until I learned how to make a really good calibration using BT 1886.

This profile/calibration was done using ARGYIICMS (Beta 1.7)

ss

CalWldLif 07-05-2014 07:33 PM

my simplistic description is that the set comes out of black quicker at low IRE and then flat lines to a 2.4 gamma after @ 10 to20 IRE/
good for sets with poor black levels

HDTVChallenged 07-06-2014 11:22 AM

Quote:

Originally Posted by sillysally (Post 25515946)
I am not going to give a opinion, simply because it doesn't mean anything. Chances are that the folks giving these opinion's have never seen a well calibrated BT 1886.

There's also the possibility that many recent video sources were mastered/graded on monitors set to PL@2.2 ... so when displayed on a monitor that's closer to 2.4 while adding ABL on top, perhaps the aforementioned source might wind up looking overly dim ... Hypothetically ... I'll probably never be able to test that hypothesis myself. :)

sillysally 07-06-2014 05:33 PM

Quote:

Originally Posted by HDTVChallenged (Post 25528362)
There's also the possibility that many recent video sources were mastered/graded on monitors set to PL@2.2 ... so when displayed on a monitor that's closer to 2.4 while adding ABL on top, perhaps the aforementioned source might wind up looking overly dim ... Hypothetically ... I'll probably never be able to test that hypothesis myself. :)

You may be able to test for yourself. When in pre calibration mode, run a simple 10 point Gamma, Grayscaly, RGB balance chart set to BT1886 2.4, and see how well that lines up. Do the same with a power 2.2 Gamma setting. Then compare the two.

I don't use any APL background, just a 8% window with a black background.

Yes you may want to increase your Contrast setting by about 2 or 3 clicks and lower your Brightness settings by the same when using BT1886 2.4. Also if you use a calibration program like ArgyII, you can make three 3DLUT's from the profile you just ran, using BT1886 2.4, BT1886 2.2 and a 2.2 Gamma. Load into a eecolor box or a HTPC and compare how all three look with some reference material.

ss

avsform1 07-06-2014 07:48 PM

I am not going to give a opinion, simply because it doesn't mean anything. Chances are that the folks giving these opinion's have never seen a well calibrated BT 1886.

Click on this link below to see for yourself how well using the BT 1886 2.4 formula can work. Once the file downloads open with your browser (internet explorer, Google, ect.)
http://s000.tinyupload.com/index.php...71250428642221

btw, I understand why some may not appreciate what the BT 1886 can really do. I used to think the same way as some of you until I learned how to make a really good calibration using BT 1886.

This profile/calibration was done using ARGYIICMS (Beta 1.7)

ss[/QUOTE]

SS,

One can see that with a 3d LUT on the eeColor would make the display fantastic! But how was your comparison of the display without the 3d LUT?

HDTVChallenged 07-06-2014 10:01 PM

Quote:

Originally Posted by sillysally (Post 25537634)
You may be able to test for yourself. When in pre calibration mode, run a simple 10 point Gamma, Grayscaly, RGB balance chart set to BT1886 2.4, and see how well that lines up. Do the same with a power 2.2 Gamma setting. Then compare the two.

It's hopeless. On my current display the MLL is ~0.12Nits and more like 0.16Nits when calibrated for ~115Nits reference white. Gamma @2.4 would just crush everything into a smokey haze. :) ... In case you're wondering, the original plan was to use it for daytime viewing and a PJ for nighttime ... and now it's 10000 hours later. ... Plans ... :eek:

PS: BT1886 2.2 ... what?

sillysally 07-07-2014 12:27 AM

Quote:

Originally Posted by avsform1 (Post 25540362)
I am not going to give a opinion, simply because it doesn't mean anything. Chances are that the folks giving these opinion's have never seen a well calibrated BT 1886.

Click on this link below to see for yourself how well using the BT 1886 2.4 formula can work. Once the file downloads open with your browser (internet explorer, Google, ect.)
http://s000.tinyupload.com/index.php...71250428642221

btw, I understand why some may not appreciate what the BT 1886 can really do. I used to think the same way as some of you until I learned how to make a really good calibration using BT 1886.

This profile/calibration was done using ARGYIICMS (Beta 1.7)

ss

SS,

One can see that with a 3d LUT on the eeColor would make the display fantastic! But how was your comparison of the display without the 3d LUT?[/QUOTE]

If you want to compare a manual normal 10PT grayscale, Gamma, RGB balance and CMS of mine, click on the last link in my sig. However that report is a typical non- comprehensive report that you may get from a Pro calibrator. If I still had the VT50 I did that calibration on and ran a much larger comprehensive report on it, the calibration would not look nearly as good as the report I have a link to in my sig.

Matter of fact, just because you do a 3DLUT calibration on a VT60 probably still will have noticeable color errors. I learned a lot about how to make a good 3DLUT using LightSpace and eecolor box (its a good and easy 3DLUT software, with great support from Steve) However I have moved on for now to ArgyIICMS along with the rest of the software that is need, manly to see how well it worked because it is a free software.
It has taken me about 3 weeks to get it working well and building my own custom patch sets, the end results you see in the report I link too in the above post. That report I linked to, the 3DLUT is made using a custom made 9405 color points and of course with GWGill (ArgyIICMS developer) gift to us all. Also a gift to us all from fhoech (dispcalGUI developer) and madshi (madVR developer).

Quote:

Originally Posted by HDTVChallenged (Post 25542786)
It's hopeless. On my current display the MLL is ~0.12Nits and more like 0.16Nits when calibrated for ~115Nits reference white. Gamma @2.4 would just crush everything into a smokey haze. :) ... In case you're wondering, the original plan was to use it for daytime viewing and a PJ for nighttime ... and now it's 10000 hours later. ... Plans ... :eek:

PS: BT1886 2.2 ... what?

BT1886 2.2 is just as it reads. Just like power 2.2 or 2.4, the difference is in the gamma curve of BT 1886 as were power 2.2 or 2.4 is flat.
I don't use a projector so take what I say with a grain of salt. If you want to know more post that question in the ArgyII/madVR thread. Also if you want to get into HTPC and therefore bypass the use and expense of the eecolor box post and start reading in that thread.

ss

sotti 07-07-2014 12:55 AM

Quote:

Originally Posted by HDTVChallenged (Post 25542786)
It's hopeless. On my current display the MLL is ~0.12Nits and more like 0.16Nits when calibrated for ~115Nits reference white. Gamma @2.4 would just crush everything into a smokey haze. :) ... In case you're wondering, the original plan was to use it for daytime viewing and a PJ for nighttime ... and now it's 10000 hours later. ... Plans ... :eek:

PS: BT1886 2.2 ... what?

BT.1886 is a specific formula designed NOT TO CRUSH!

BT.1886 is formula that adjust the response of your display along a power curve of 2.4, but it matches the curve to your black floor, so you get excellent shadow detail while still have an image with a bit of punch.

All of this is designed to emulate the way CRTs performed and give us a repeatable standard that we can calibrate to.

In no way should BT.1886 be compared to a simple power law calibration.

HDTVChallenged 07-07-2014 02:54 PM

Quote:

Originally Posted by sillysally (Post 25544162)
SS. If you want to know more post that question in the ArgyII/madVR thread. Also if you want to get into HTPC and therefore bypass the use and expense of the eecolor box post and start reading in that thread.

No interest in either "solution" for my current display. There's very little that a 3D LUT would be able to improve and no chance of fixing the one big "flaw" of the display ... which isn't really a flaw if I were using it as I originally planned. ;)

Perhaps I should clarify: When I said, 'There was little chance of testing my hypothesis," what I meant was that it is very unlikely that I'll get my hands on a plasma at this point ... and my current display doesn't suffer from ABL. Therefore, I can't really test the hypothesis. All I can do is engage in thought experiments. :)

HDTVChallenged 07-07-2014 03:03 PM

Quote:

Originally Posted by sotti (Post 25544394)
BT.1886 is a specific formula designed NOT TO CRUSH!.

No argument there. :) When I said, "Gamma @2.4," read "Power Law with gamma =2.4." BT1886 is not gamma, it's an EOTF ;)

My point was that the phrase BT1886 2.2 makes no sense. The "gamma" of BT1886 is always 2.4. This is why the practice of using "Gamma" (a variable name) to refer to a specific EOTF (namely the power law function) should be exterminated ... Although, I realize it's probably hopeless at this point.

Edit:

Actually from a practical calibration standpoint it *is* useful to compare BT1886 to straight power law, if only to help pick the best power-law "gamma" preset from which to start. You wouldn't want to start with 2.4 if your projected BT1886 curve is closer to 2.2. In my case, the average power law "gamma" of the BT1886 curve is ~2.15, so if I were to start with the gamma preset =2.4, I'd be doing a *lot* more luminance cranking in the 10pt ... particularly at the dark end.

gwgill 07-10-2014 03:44 AM

Quote:

Originally Posted by HDTVChallenged (Post 25558786)
My point was that the phrase BT1886 2.2 makes no sense. The "gamma" of BT1886 is always 2.4.

BT.1886 uses an input black point offset strategy, so it is more accurate to say "an EOTF using input black offset and a power of 2.2", but "BT.1886-like with a power of 2.2" is fine by me too.
Quote:

Originally Posted by HDTVChallenged
Actually from a practical calibration standpoint it *is* useful to compare BT1886 to straight power law,

Except that in practice, there really isn't such a think as a "straight" power law, since in general no display has a zero black level. So I have a strong suspicion that what people actually mean when they say this sort of thing (whether they know it or not) is that they want an output black point offset strategy with the given power.


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