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Gamma closer to CRT

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Alessa Reznik
Gamma closer to CRT
on Dec 7, 2010 at 12:35:10 am

I'm finding on my 2470 that to closer resemble a CRT I need gamma set to 2.4, actually more like 2.6

Anyone else find this


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walter biscardi
Re: Gamma closer to CRT
on Dec 7, 2010 at 1:02:01 am

You really don't want to "resemble a CRT." You want to resemble proper gamma for whatever it is you're doing. Rec 709 for most of us in HD.

And which CRT are we talking about? Sony PVM series looks different than the BVM series for example. JVC looks different than Sony, etc....

Walter Biscardi, Jr.
Editor, Colorist, Director, Writer, Consultant, Author, Chef.
HD Post and Production
Biscardi Creative Media

"Foul Water, Fiery Serpent" Winner, Best Documentary, LA Reel Film Festival...

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Chris Wiggles
Re: Gamma closer to CRT
on Mar 4, 2011 at 8:18:38 pm

[walter biscardi] "You really don't want to "resemble a CRT." You want to resemble proper gamma for whatever it is you're doing. Rec 709 for most of us in HD."

I just want to point out that this is a common misconception.

Rec. 709 *does not* define display gamma. At all.

There is no explicit studio standard for display gamma.

Regards,
Chris


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Bram Desmet
Re: Gamma closer to CRT
on Mar 4, 2011 at 8:32:22 pm

Correct, in that it is not defined by the Rec 709 standard and is not defined (currently) by SMPTE. However, I would not go as far as to say "There is no explicit studio standard for display gamma", unless you want to completely discount Europe. The EBU does recommend a nominal value of 2.35. Also, in North America, when dealing with displays where gamma is in fact adjustable/programmable, 2.2 has become a defacto standard within many organizations. The discussion of whether it should be is of course a whole other matter.

All of this being said, with respect to FSI monitors specifically you can instantly select whatever gamma response you like (1.0, 1.8, 2.0, 2.2, 2.35, 2.4, 2.6, 2.8). They are all programmed in during the alignment process and can be instantly recalled from a simple menu selection.

Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com


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Chris Wiggles
Re: Gamma closer to CRT
on Mar 4, 2011 at 8:53:02 pm

You are right, EBU thankfully does explicitly define display gamma of 2.35. Forgot about that one.

I thoroughly agree with Poynton here about the need to define display gamma, because there are MANY people who think that 2.2 is reference gamma and sadly it has sort of just become a de-facto reference for a lot of people for absolutely no good reason except that there is no explicit standard and people are confused. And quite a few of them appear to think that 2.2 is defined somewhere as a display gamma, when that is not the case (except for sRGB which is not a video standard). So what mastering houses are doing is all over the map. This leaves consumers unable to calibrate to a single gamma, because you don't know if something was mastered at say 2.2, or 2.35, or 2.5, or 2.6, or what. And the difference between 2.2 and 2.6 is HUGE. We can quibble about slight gamma issues, but once you're talking about the ranges of gammas I hear people talking about calibrating to, you quickly realize that everyone is just flying by the seat of their pants and just making up whatever value they want because "it looks good to me." And that's not a way to run a professional technical field... :(


http://www.poynton.com/notes/PU-PR-IS/Poynton-PU-PR-IS.pdf

Quote:

BT.709 proposals
To achieve accurate representation of the director or cinematographer’s
visual experience, standardization of the reference display EOCF
is necessary. I propose to codify current practice and standardize
today’s 2.4-power function as part of BT.709 and its derivatives. For
creative purposes, there is no need to standardize OECF; however,
retaining a reference OECF is sensible for engineering reasons.
I propose these improvements to BT.709 and its SMPTE and EBU
derivatives. My recommendations essentially codify current practice:

1
Pertinent display characteristics and reference viewing conditions
should be standardized. I propose that the studio reference display
should have reference white luminance of 100 cd·m^-2
at CIE D65. Veiling glare should be specified at approximately 0.2% of reference white. The display should be viewed in a 50% diffuse neutral grey surround having 5% of the luminance of reference white. Standards
groups should consider the manner in which viewing parameters have
been specified in the sRGB standard, the opRGB (AdobeRGB) standard,
and in ISO and ICC documents, and should consider discussions that
have taken place within the colour management community.

2
EOCF of a studio reference display should be standardized based upon
a 2.35-power function. (Other values such as 2.36 and 2.4 have been
proposed; any value between 2.35 and 2.4 would serve.)

3
BT.709’s current OECF should be retained as a reference for engineering
purposes. BT.709 should make clear that its OECF is appropriate
for studio scenes, and that modifications of the OECF for
creative purposes – perhaps dramatic modifications – should be
routinely expected. A statement is needed saying that encoding
should be arranged such that the intended image appearance is
obtained on the reference display in the reference viewing conditions.

4
Standards should discuss – or at a minimum, mention – image state as
that term is used in the colour management community. In particular,
BT.709 and its derivatives should be clarified to explain that the reference
OECF included in the standard is meant to exemplify capture of
a typical studio scene, and that the video signal (image data) is output
(display) referred.



I highly support and applaud monitor flexibility in the gamma LUT to allow a quick and easy selection and adjustment for a very broad range of gammas. Not simply for calibration needs, but also for sanity-checking your content on a variety of gammas. We need more manufacturers to adopt that approach.

Regards,
Chris


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diego delanoe
Re: Gamma closer to CRT
on Mar 30, 2012 at 4:31:17 pm

Hello Bram, i have a flanders 2461w, with the default 2.2 gamma, but i was reading a colorist book that states that for rec 709 it should be used a 2.5 gamma setting, and there's no 2.5 on the flanders.
I also would like to ask about the workflows, for example, what settings to use when working on HD, but inteded to finish in SD or internet HD or dvd, ect.

Thanks!

THE PANIC PROPAGANDA


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Bram Desmet
Re: Gamma closer to CRT
on Mar 30, 2012 at 4:40:01 pm

Hi Diego, I would not suggest 2.5...not sure the context for recommending 2.5 for rec709 footage, but it is not what is commonly done. The default when shipped in North America or reset to 'factory' default is 2.2, but what is extremely common is to switch the gamma response to 2.35 or 2.4. That is my personal preference and a good setting to use. We offer gamma adjustment in 0.2 step increments because the difference even at that level is fairly subtle from step to step. 2.6 and 2.5 will be largely indistinguishable so if you really want a 2.5ish type gamma set it to 2.6 and that will get you extremely close...again though, not what I would suggest, 2.4 would be a better bet.

Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com


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diego delanoe
Re: Gamma closer to CRT
on Mar 30, 2012 at 8:36:19 pm

Thanks Bram, this is what says on the Color Correction Handbook, by Alexis Van Hurkman,

"2.5: This is the gamma for both SD and HD video displays as defined by the rec. 709 standard. 2.5 is the gamma standard you should adhere to when select a display for color correction work"

Why would you recommend the 2.4 over the 2.6?

So for HD material finishing in SD, wich gamma is the apropiate, 2.2 or 2.4?

Thanks a lot.

THE PANIC PROPAGANDA


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Bram Desmet
Re: Gamma closer to CRT
on Mar 30, 2012 at 8:45:41 pm

Hi Diego, give this a read: http://vanhurkman.com/wordpress/?p=1216

That should clear up the confusion for you and confirm my earlier suggestion.

Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com


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diego delanoe
Re: Gamma closer to CRT
on Apr 26, 2012 at 11:42:13 pm

Hello Bram,
Im a bit confused with so much information so i would like to ask an expert.
If im working with hd material, thats going to be finished to HD for proyection (not cinema, just standart projector),and also end up in a sd DVD, wich color space should i use, rec 709 or smpte C, and wich gamma???
Please some help!!

THE PANIC PROPAGANDA


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Bram Desmet
Re: Gamma closer to CRT
on Apr 26, 2012 at 11:51:02 pm

I would suggest Rec709 and 2.2 gamma. For Europe 2.35 gamma. When talking about theatrical exhibition outside of a DCI workflow you will find a lot of varying advice on gamma settings, but the numbers above are probably your best bet if also going out to DVD without further adjustment.

Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com


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diego delanoe
Re: Gamma closer to CRT
on Apr 26, 2012 at 11:55:34 pm

Thanks Bram,
You are a big help!

THE PANIC PROPAGANDA


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Alessa Reznik
Re: Gamma closer to CRT
on Dec 7, 2010 at 1:53:19 am

Hi Walter

Thanks for the response, I'm comparing footage graded on calibrated BVM Sony

Have you kept all original factory settings on your displays?

I know plasmas and lcds have a brighter look compared to CRT especially when grading dark scenes, also i realize that nowadays no one has crt's at home.

I'm just concern of having my graded footage being qc'd on a CRT and it looking much darker than than when viewed on my display

Do you use ND glass in front of your displays?

Thanks

I'm very happy with the 2470


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walter biscardi
Re: Gamma closer to CRT
on Dec 7, 2010 at 1:57:49 am

[Alessa Reznik] "
Have you kept all original factory settings on your displays?"


Yes, we are working in HD Rec 709 and the monitors are calibrated for us by FSI.



[Alessa Reznik] "I'm just concern of having my graded footage being qc'd on a CRT and it looking much darker than than when viewed on my display

Do you use ND glass in front of your displays?"


I've not had that issue using the FSI's. What we grade on the monitors looks more or less the same on every other properly calibrated monitor including CRTs. That's why we use the FSI's, they are accurate Grade 1 reference monitors.

The newer displays do not use ND glass any longer. We are getting rid of our older model 2450W's that had the glass on them and going with 2460Ws for all our suites. The Davinci Resolve suite is getting the 2470W

Walter Biscardi, Jr.
Editor, Colorist, Director, Writer, Consultant, Author, Chef.
HD Post and Production
Biscardi Creative Media

"Foul Water, Fiery Serpent" Winner, Best Documentary, LA Reel Film Festival...

Blog Twitter Facebook


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Bram Desmet
Re: Gamma closer to CRT
on Dec 7, 2010 at 3:57:42 am

2.2 is the default gamma of the 2470W, but you can instantly change this to any value you like. Per the EBU's recommendation 2.35 would be the setting to select to most closely replicate the 'average' grade 1 CRT. Most of our customers in North America prefer to use 2.2, most of our customers in Europe use 2.35.

Bram Desmet
FSI (Flanders Scientific, Inc.)
http://www.FlandersScientific.com


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