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post #1 of 31 Old 10-28-2011, 11:50 PM - Thread Starter
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I read quite a few posts where VT25 Panny was used for color editing of
TV shows.
What I could not find is at what footlambers and gamma was used.
Anyone know?
One reason is I also read bluRays were being edited to a 2.4 gamma.

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post #2 of 31 Old 10-29-2011, 02:26 AM
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I've never seen a TV or projector where 2.4 looked right... it always seems to be too dark. 2.3 works on some displays and 2.2-2.25 is good for others (especially if they haven't got inky-dark blacks). Gamma is a huge arguement just looking for every and any excuse to get started again.

The real final arbiter is... if 2.4 gamma makes the display look too dark, don't use it. Use 2.35 or 2.3 or 2.25... whatever looks right to you. If the gamma number is too high everything from 1% white to 99% white will look too dark. When gamma is optimized, shots with good perspective and distance in them will look more 3D dimensional without seeming too dark. If the gamma number is too low, everything from 1% white to 99% white will be too bright and images will appear too flat, like a slightly over-exposed photo.

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post #3 of 31 Old 10-29-2011, 07:29 AM
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Thanks Doug, another helpful and very clear explanation!
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post #4 of 31 Old 10-29-2011, 08:23 AM
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It looks like in the near future that 2.4 will become the official standard that material is mastered against but that is based on a totally light-controlled room as well. I'm working on an article about this now but the correct answer is still "use the gamma that works for your room".

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post #5 of 31 Old 10-29-2011, 11:06 AM
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Quote:
Originally Posted by Smackrabbit View Post

It looks like in the near future that 2.4 will become the official standard that material is mastered against but that is based on a totally light-controlled room as well. I'm working on an article about this now but the correct answer is still "use the gamma that works for your room".

This is entirely accurate.

The BT.1886 specification has an exponent of 2.4, but it also has a black offset, so as an absolute gamma curve, it ramps much more quickly out of black.

The BT.1886 spec doesn't define a viewing environment, which is a short coming, but it is designed for the standard authoring environments which typically has very low light.

If you have a brighter room, targeting a lower gamma is an appropriate thing to do.

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post #6 of 31 Old 10-29-2011, 11:35 AM - Thread Starter
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Thanks guys.
I do notice what low vs high gamma numbers do.
Also how the overall
brightness effects pic.

Over the last say 3-5 years i have seen a definite lowering of APL/ABL of broadcast TV. Just curious if some standard changed and i would like to calibrate to it.
I first noticed on CRT
Mitsubishi Diamond 40".

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post #7 of 31 Old 10-29-2011, 12:17 PM
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I suspect if there is a change in the gamma spec to 2.4 it will be a huge mistake. It should be fixed at 2.22 or left alone. This is even more true as black levels fall as technology changes and near black is obscured by inadequate ANSI contrast.

How the encode/decode process uses gamma should not be changed. If it does it will be similar to deciding on when to use and not use SMPTE color space versus RGBs for DVDs. You will not know when to switch. There is a ton of gear already out there with what is an effective 2.2 gamma on the display side. Suddenly switching to using 2.4 will wreak things for little if any gain. You can already alter the gamma of an image in post if you want to enhance contrast.

It is obvious looking at sources that all most all are setup for a 2.22 gamma as Doug has said. If you look at the specs for the Sony reference monitors they are 2.22 gamma by default. I have also worked in post with a RED camera and a 2.22 gamma on the decode looks great while 2.4 is too dark.

Varying gamma with room light level does not appear to work to me. I would alter light output and black level instead.
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post #8 of 31 Old 10-29-2011, 01:11 PM - Thread Starter
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Quote:
Originally Posted by umr View Post

I suspect if there is a change in the gamma spec to 2.4 it will be a huge mistake. It should be fixed at 2.22 or left alone. This is even more true as black levels fall as technology changes and near black is obscured by inadequate ANSI contrast.

How the encode/decode process uses gamma should not be changed. If it does it will be similar to deciding on when to use and not use SMPTE color space versus RGBs for DVDs. You will not know when to switch. There is a ton of gear already out there with what is an effective 2.2 gamma on the display side. Suddenly switching to using 2.4 will wreak things for little if any gain. You can already alter the gamma of an image in post if you want to enhance contrast.

It is obvious looking at sources that all most all are setup for a 2.22 gamma as Doug has said. If you look at the specs for the Sony reference monitors they are 2.22 gamma by default. I have also worked in post with a RED camera and a 2.22 gamma on the decode looks great while 2.4 is too dark.

Varying gamma with room light level does not appear to work to me. I would alter light output and black level instead.

good to know. thank you

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post #9 of 31 Old 10-31-2011, 06:37 PM
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....If you look at the specs for the Sony reference monitors they are 2.22 gamma by default....

Negative! I've got the specs for a number of Sony BVM reference monitors (including the F24), and gamma is not only NOT SPECIFIED, but it isn't even mentioned in their literature, -anywhere-. A person affiliated with THX who claims to have actually MEASURED a number of BVM CRT reference monitors, says they generally fall within the range of 2.35 to 2.7. He also claims that the MEASURED color temperature of these same monitors "calibrated" to D65 actually read between 5900 and 6300 K. My JVC DT Grade-2 monitor supposedly had its gamma characteristic designed to match the look of the BVM, and when I look at what I believe to properly produced and graded material, it generally looks dead nuts - it's neither too bright nor too dark and the image needs NO ADJUSTMENT. Extensive research conducted by the BBC, indicates that the ideal value of gamma for DIRECT VIEW displays to lie between 2.3 and 2.4, and the EBU specifies 2.35 for Grade-1 monitoring equipment. Maybe if everyone got off of this gamma = 2.2 kick, the issue wouldn't keep coming up over-and-over again.
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post #10 of 31 Old 11-01-2011, 07:16 AM
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Fastl is quite right. EBU states gamma, for grade 1 monitors, to be 2.35. Sony monitors do not specify the Gamma target. I'm assuming, being CRT, that they are naturally 2.35? Not sure how they would manage 2.2 for NTSC? Is it electronically manipulated?

Also, you're right in saying that D65 does not seem true. I was thinking my calibration gear was out. However, it does measure noticeably warmer than D65.

Strange, as Sony monitors are well respected in the broadcast industry and strict tolerances are specified for grade 1 monitors.
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post #11 of 31 Old 11-01-2011, 09:40 AM
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An example of this from a real monitor is the preset gamma of 2.2 for the BVM-L231. This is Sony’s color grading monitor at this time. An excerpt from page 53 of the operating manual that shows this is shown below.

Many peoples measured gammas are off because their meters are poor when things get dark.
LL
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post #12 of 31 Old 11-01-2011, 06:05 PM
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The BVM-L231 is not a very good example for this discussion since it was considered by many to be a failure and I don't know anyone of note that is seriously using them for high quality grading. The E250 is the new standard. When you say BVM, most people familiar with this monitor line assume CRT, not LCD, and the CRT monitors are not characterized by a 2.2 gamma. My DT-V24L1D is around 2.4, and it works. I can attest to it.
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post #13 of 31 Old 11-01-2011, 11:03 PM
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The simple fact is that now, unless you know the person that is doing the final mastering, there is really no way to be certain what gamma it was mastered at, and if your display is running the correct gamma. I've talked to people now that are pro-2.4 and pro-2.2, but in the long run it seems that having an actual standard is what is desirable. I've also heard that certain studios have already been mastering their films for a gamma of 2.4, in which case most people have their displays calibrated to a different standard but don't realize it. i think having a standard is good, but I'm not in the position to say what I think it should be.

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post #14 of 31 Old 11-03-2011, 12:17 PM
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IMO it would be absolutely STUPID to pick 2.4 as a mastering standard at this point in time. I've NEVER measured a consumer video display from a smallish $500 panel to $10,000+ projectors that are anywhere close to 2.4 out of the box and most of them have no gamma setting that would put the display very close to 2.4 gamma. That means the ONLY displays that would have 2.4 gamma would be CALIBRATED displays BUT not all consumer displays can even be calibrated to achieve 2.4 gamma... in fact, I'd go as far as saying a good half or more of consumer displays won't achieve 2.4 gamma with the settings available in the user menu or service menu.

THEN there's this issue... suppose you do have a TV or projector that does 2.4 gamma out of the box. What the hell are you going to do about the 61+ years of video and film that was mastered on CRT displays with considerably lower gamma (probably closer to 2.2)? Are you going to change gamma for older 2.2 sources and raise it for 2.4 sources? And what about all the video cameras shooting with gamma curves that are something other than 2.4? Will every one of them have to be re-calibrated to the 2.4 standard? And if that happens, how will people at home "fix" their TV if there are no gamma settings anywhere?

It's a big damn mess and IMO, the only RIGHT thing to do is to make everything conform to 2.3 gamma and forget about it. That way a display that's 2.0 or 2.1 gamma won't look too extreme (if the mastering gamma is 2.4) and if something is mastered at 2.4 or 2.5, a display with 2.3 gamma won't look too bad either. And if the display and the original material are both 2.3... that will be as good as it gets. We just can't set a standard in a vacuum... the outside world needs to be taken into account.

Actually, I just had another thought... why have gamma at all? Gamma only exists because it was prohibitively expensive to make TVs with linear response back in the 1940s and 1950s -- and there was a bandwidth side-benefit for broadcast. Since all broadcasting is now digital and all displays are now digital, we could EASILY banish gamma entirely in favor of linear light response... record everything linear, master everything linear, playback everything linear. All you'd need is a setting somewhere in the playback chain (or in multiple places, like cable/satellite boxes, disc players, etc.) so that if they are connected to a "legacy" video display, they would convert the 1.0 gamma sources to 2.2 or so. But consumers are totally unlikely to be able to deal with this complexity (even though it's just 1 setting that needs to be done 1 time) so it would probably be best for these sources to output 2.2 or 2.3 gamma all the time unless connected to a new-fangled linear display which could all be done in the handshake so the player would automatically switch to linear response when connected to a linear display.

There's no longer an absolute necessity for a gamma "curve" in video, what we fight now is having enough bits in the shadows and highlights to prevent banding and that we allocate bits well enough to avoid banding in the midtones also (if you allocate too many bits to the shadows and highlights, you can "starve" the midtones for bits and end up with visible banding in the midtones. The best solution would be 12-bit video with linear (no gamma) response... the additional bits provide enough bits in shadows, midtones, and highlights to avoid banding.

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post #15 of 31 Old 11-03-2011, 01:13 PM
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While the exponent for the BT.1886 formula is 2.4, the formula is not stim^2.4

This is the formula:
L=a(V+b)^2.4

a and b are derived from the white level and black level.


The result is that the gamma curve for a display with a black level of 0.05 cd/m2 and a white level of 120 cd/m2 looks like:
Point:


Log:


Absolute:



And for reference here is what sRGB looks like in point:

LL
LL
LL
LL

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post #16 of 31 Old 11-03-2011, 05:49 PM
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Thru the critical midrange, it sure doesn't look like 2.2 to me!
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post #17 of 31 Old 11-04-2011, 01:39 PM
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Today's calibration software tries to set every grayscale step to the same gamma value. So if you were to graph gamma from 10% to 90% (there is no "gamma" for 100% or 0% since those are the white point and black point) and you set the gamma target to 2.3, you'd get a horizontal line from 10% to 90% at the 2.3 gamma. So this new formula appears to set gamma at 2.3 for 99% (again, there is no gamma value for 100%) and gamma drops from there.

This will look like CRAP on current TVs that are "expecting" a linear gamma. And today's TVs will NEVER be able to achieve a gamma that looks anything close to the curve in those graphs. So, my original comment still stands... if something like this is implemented, there must be an accommodation for legacy disc players, processors, and video displays that results in the linear gamma those products were designed for. The only time you could/should be able to implement a "curve" to gamma would be if the playback chain can accommodate it (and that would mean something "extra" in the handshake so the playback chain would know if it will handle a non-linear gamma.

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post #18 of 31 Old 11-04-2011, 02:06 PM
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Quote:
Originally Posted by Doug Blackburn View Post

Today's calibration software tries to set every grayscale step to the same gamma value. So if you were to graph gamma from 10% to 90% (there is no "gamma" for 100% or 0% since those are the white point and black point) and you set the gamma target to 2.3, you'd get a horizontal line from 10% to 90% at the 2.3 gamma. So this new formula appears to set gamma at 2.3 for 99% (again, there is no gamma value for 100%) and gamma drops from there.

This will look like CRAP on current TVs that are "expecting" a linear gamma. And today's TVs will NEVER be able to achieve a gamma that looks anything close to the curve in those graphs. So, my original comment still stands... if something like this is implemented, there must be an accommodation for legacy disc players, processors, and video displays that results in the linear gamma those products were designed for. The only time you could/should be able to implement a "curve" to gamma would be if the playback chain can accommodate it (and that would mean something "extra" in the handshake so the playback chain would know if it will handle a non-linear gamma.

And just in case you are wondering we are calculating the 100% at 99.99% and the 0% at 0.01%

The fact that this curve is so similar to sRGB should mean something. sRGB was also designed to emulate the response of the CRTs of the late 90s.

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post #19 of 31 Old 11-05-2011, 04:45 AM
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As both a professional colourist, and calibrator for professional post-production operations, all I can say is that a display gamma of 2.2 is the industry standard, with approx 23FtL as peak white.

Also for TV colour work (which the above figures are for) the grading room is illuminated to approximate a 'normal' living room environment... what ever that means, the reality is a room similar to your lounge at night with a few room lamps on.

For film grading, things are rather different, but for all films that end up on DVD or BlueRay, etc., they are re-mastered (sometimes by re-grading, some times via a LUT application) to adhere to the above TV figures for display.

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post #20 of 31 Old 11-05-2011, 06:49 PM
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...As both a professional colourist, and calibrator for professional post-production operations, all I can say is that a display gamma of 2.2 is the industry standard, with approx 23FtL as peak white....

Which standard? Your's or the industry's? SMPTE RP 166 (Critical Viewing Conditions for Evaluation of Color Television Pictures) clearly specifies 35 ft/L as peak white, with a 10% background illumination. It is true that the CRT BVM's couldn't make 35 ft/L without having the resolution of the monitor seriously impaired due to beam spreading, so they had to be run at lower levels. That doesn't make it "standard", just common practice. Of course this is not an issue with LCD or OLED monitors, since they easily can be run at the 35 ft/L standard level.

If your look at Dolby's PRM-4200 reference monitor, and select CRT reference mode, the gamma is set to a default value of 2.35. Same goes for the Barco RHDM-2301. It's not just a co-incidence that they both default to 2.35.

From EBU TECH 3320: The gamma characteristics (electro-optical transfer characteristic) of the screen should be equivalent to those of a reference CRT with the rendering intent (dim-surround) expected of a TV system, once offsets of signal level at black and residual brightness at black have been removed. We believe that a value of 2.35 is appropriate. See Annex A and the Note below....The television system has been deliberately designed with an end-to-end system
gamma of about 1.2, to provide compensation for the dim surround' effect [6]. Therefore the monitor gamma is not, and never has been, the inverse of the camera gamma....The conclusion must be that any new monitor technology should retain the same electro-optical characteristic as has historically been used. BBC R&D Report RD 1991/6, Methods of measuring and calculating display transfer characteristics (gamma)' by Alan Roberts, indicates a method of performing such measurements, and has yielded results which indicate that the gamma of a grade 1 CRT monitor is typically in the region of 2.3 to 2.4.....

Charles Poynton goes into this whole subject in much greater detail and also confers with the 2.4 number. A gamma value of 2.2 may work well in a consumer environment where peak white is turned up a lot higher than 35 ft/L and where the ambient illumination is also higher than 3.5 ft/L, but such a viewing environment would not be considered a "standard" viewing environment.
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post #21 of 31 Old 11-06-2011, 09:54 AM
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*operational standard.

The specs as defined by SMPTE and others have never been adhered to within the post production industry, partly because of the CTR 'blooming' issue mentioned.

So, as the operational 'norm' it would make sense to follow this, would it not?

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post #22 of 31 Old 11-06-2011, 05:34 PM
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Although other users of the CRT master monitors were forced to run their peak white levels below the 35 fL standard, I'm not aware that they decided to run them at 2.2 gamma like you do. Anyway, you're asking the wrong guy. Why don't you rattle Glimmie's cage and ask him? He works for Technicolor. I'm sure he probably has a good idea of how the grading monitors are set up.
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post #23 of 31 Old 11-09-2011, 12:24 PM
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Quote:
Originally Posted by umr View Post

I suspect if there is a change in the gamma spec to 2.4 it will be a huge mistake. It should be fixed at 2.22 or left alone. This is even more true as black levels fall as technology changes and near black is obscured by inadequate ANSI contrast.

How the encode/decode process uses gamma should not be changed. If it does it will be similar to deciding on when to use and not use SMPTE color space versus RGBs for DVDs. You will not know when to switch. There is a ton of gear already out there with what is an effective 2.2 gamma on the display side. Suddenly switching to using 2.4 will wreak things for little if any gain. You can already alter the gamma of an image in post if you want to enhance contrast.

It is obvious looking at sources that all most all are setup for a 2.22 gamma as Doug has said. If you look at the specs for the Sony reference monitors they are 2.22 gamma by default. I have also worked in post with a RED camera and a 2.22 gamma on the decode looks great while 2.4 is too dark.

Varying gamma with room light level does not appear to work to me. I would alter light output and black level instead.

Setting 2.4 as a standard would not change anything. Content is already mastered at 2.4 gammait's what BVM CRTs run at (actually, a little higher near black) and the new OLED monitors are a flat 2.40 down to black.

2.22 is for PC monitors. (it should really be the sRGB transfer function, but everyone uses 2.22)

Quote:
Originally Posted by umr View Post

An example of this from a real monitor is the preset gamma of 2.2 for the BVM-L231. This is Sony's color grading monitor at this time. An excerpt from page 53 of the operating manual that shows this is shown below.

Many peoples measured gammas are off because their meters are poor when things get dark.

The LCD monitors used 2.2 because, being low-contrast LCDs (1,000:1 if I recall correctly) they were incapable of anything remotely close to an accurate 2.4 gamma. The CRTs were 2.4, and the new OLEDs are also 2.40 (with an optional mode to emulate the imperfect CRT gamma)
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post #24 of 31 Old 11-10-2011, 02:31 AM
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Quote:
Originally Posted by Chronoptimist View Post

Setting 2.4 as a standard would not change anything. Content is already mastered at 2.4 gammait's what BVM CRTs run at (actually, a little higher near black) and the new OLED monitors are a flat 2.40 down to black.

I've heard this arguement before and it's goofy for 2 reasons... every time someone actually measures one of those old pro monitors, they come back saying it measured 2.2 or a little higher but not much higher. AND, it really doesn't matter a frack what the display gamma runs at, the system feeding it can manipulate gamma in any way, up or down, or S-shaped or any profile you want it to have.


Quote:
Originally Posted by Chronoptimist View Post

The LCD monitors used 2.2 because, being low-contrast LCDs (1,000:1 if I recall correctly) they were incapable of anything remotely close to an accurate 2.4 gamma. The CRTs were 2.4, and the new OLEDs are also 2.40 (with an optional mode to emulate the imperfect CRT gamma)

There are multiple considerations for gamma. Room lighting conditions are at least as meaningful as the black level of the display being used for mastering. Room lighting conditions will make different gammas other than the mastering gamma more satisfactory. It is my experience that EVERYTHING in the image looks too dark even in a dark (blacked-out) room with the display gamma set to 2.4. Afterall, gamma (ideally) does not affect the black point or white point at all, but it makes EVERYTHING between black and white darker or lighter... it's not just a shadow thing and not just a highlight thing... the entire midtone range moves up and down as gamma moves up and down and anything higher than about 2.3 gamma just plain looks too dark in spite of how good the display's black level is. There are huge numbers -- millions -- of consumer displays out there right now that can't come remotely close to 2.4 gamma. In fact, they will measure 2.0 gamma, on average, and usually don't even have a control to set gamma to some other number.

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post #25 of 31 Old 11-10-2011, 05:50 AM
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At the end of the day, it is the end users preference and environment that determines the gamma. Some may find 2.35 too dark, however, this may have been the intention of the director to film it that dark, or it could be that the production monitor gamma was incorrectly set?

I must say, living in Europe, the EBU recommendation of 2.35 seems to be the best for me , when viewing material. 2.2 tends to be too washed out...
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post #26 of 31 Old 11-11-2011, 04:00 PM
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Quote:
Originally Posted by Doug Blackburn View Post

I've heard this arguement before and it's goofy for 2 reasons... every time someone actually measures one of those old pro monitors, they come back saying it measured 2.2 or a little higher but not much higher. AND, it really doesn't matter a frack what the display gamma runs at, the system feeding it can manipulate gamma in any way, up or down, or S-shaped or any profile you want it to have.

If they measure 2.2, then they have not been set up correctly. The only source for data measured from a broadcast CRT I have seen that showed 2.2 gamma was from Dr. Raymond Soniera over at displaymate, and that was from an incorrectly set-up PVM monitor (176 nits white!) rather than a BVM reference monitor.

The companies making the monitors agree that they're 2.4 (such as Sony using 2.4 gamma with their new OLED monitors, Barco using 2.35 as standard on theirs) and so do the standard bodies such as the EBU, ARIB and apparently now the ITU.

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It is my experience that EVERYTHING in the image looks too dark even in a dark (blacked-out) room with the display gamma set to 2.4. Afterall, gamma (ideally) does not affect the black point or white point at all, but it makes EVERYTHING between black and white darker or lighter... it's not just a shadow thing and not just a highlight thing... the entire midtone range moves up and down as gamma moves up and down and anything higher than about 2.3 gamma just plain looks too dark in spite of how good the display's black level is.

That is how I would describe either a display that does not have sufficient contrast to support a 2.4 gamma, or a display that averages 2.4 gamma, but does not measure 2.4 gamma at each point.

There are many displays on the market right now that will average 2.4 gamma, but when you have them calibrated to higher gammas, the response tends to be S-curved with higher-than 2.4 gamma near black, and lower than 2.4 gamma near white.

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There are huge numbers -- millions -- of consumer displays out there right now that can't come remotely close to 2.4 gamma. In fact, they will measure 2.0 gamma, on average, and usually don't even have a control to set gamma to some other number.

That doesn't really change anything. Those displays are already completely inaccurate.

Broadcast monitors are 2.4 gamma already, but it is not a defined standard, so some may be set up incorrectly. Many people believe that the BT.709 spec defines a 2.2 display gamma, when it does not specify one at all if you read the document, for example.
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post #27 of 31 Old 11-11-2011, 05:46 PM
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Chronoptimist, is quite right. Calibration is all about ensuring that what we see on our displays mimics, as close as possible, the directors/production display. This means that as well as accurate colour quality/greyscale, gamma needs to be as close to the specifications that grade 1 broadcast monitors adhere to.
The picture quality is greatly affected, if not more than, by gamma than other parameters such as colour accuracy
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post #28 of 31 Old 11-12-2011, 09:38 AM
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Originally Posted by delphiplasma View Post

Chronoptimist, is quite right. Calibration is all about ensuring that what we see on our displays mimics, as close as possible, the directors/production display. This means that as well as accurate colour quality/greyscale, gamma needs to be as close to the specifications that grade 1 broadcast monitors adhere to.
The picture quality is greatly affected, if not more than, by gamma than other parameters such as colour accuracy



What about these previous posts?

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Originally Posted by Light Illusion View Post

As both a professional colourist, and calibrator for professional post-production operations, all I can say is that a display gamma of 2.2 is the industry standard, with approx 23FtL as peak white.

Also for TV colour work (which the above figures are for) the grading room is illuminated to approximate a 'normal' living room environment... what ever that means, the reality is a room similar to your lounge at night with a few room lamps on.

For film grading, things are rather different, but for all films that end up on DVD or BlueRay, etc., they are re-mastered (sometimes by re-grading, some times via a LUT application) to adhere to the above TV figures for display.

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*operational standard.

The specs as defined by SMPTE and others have never been adhered to within the post production industry, partly because of the CTR 'blooming' issue mentioned.

So, as the operational 'norm' it would make sense to follow this, would it not?

While standards are important (and needed), at the end of the day, duplicating the actual monitoring environment that is utilized in post-production and mastering will replicate closest to the original intent, whatever that may be. Which is, in itself, another involved discussion.

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post #29 of 31 Old 11-12-2011, 04:32 PM
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It looks like in the near future that 2.4 will become the official standard that material is mastered against but that is based on a totally light-controlled room as well. I'm working on an article about this now but the correct answer is still "use the gamma that works for your room".

Please provide a link to your article here (or start a thread about it) when you're done, cuz I and probably also others would like to give it a look.

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post #30 of 31 Old 11-12-2011, 04:45 PM
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Please provide a link to your article here (or start a thread about it) when you're done, cuz I and probably also others would like to give it a look.

It's an ITU recomendation BT.1886, the graphs above from me are accurate to their published spec.

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