Gamma values used on your systems? - Page 4 - AVS Forum
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post #91 of 395 Old 08-08-2009, 01:04 PM
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And from that document you just posted:
Quote:


A CRT is characterized by a power function, but including a black-level offset term: L = (V'+ ε)^γ. Usually, γ has a value quite close to 2.5; if you're limited to a single-parameter model, L = (V'+ ε)^2.5 is much better than L = (V')^γ. The exponent itself varies over a rather narrow range, about 2.35 to 2.55. The alleged wide variation comes from variation in offset term of the equation, not the exponent: Wide variation is due to failure to correctly set the black level.

Gamma correction is roughly the inverse of this equation, but two alterations must be introduced to achieve good perceptual performance. First, a linear segment is introduced into the transfer function, to minimize the introduction of noise in very dark areas of the image. Second, the exponent at the encoder is made somewhat greater than the ideal mathematical value, in order to impose a rendering intent that compensates for subjective effects upon image display.

and
Quote:


A conventional CRT has a power-law response to voltage: Luminance produced at the face of the display is approximately the applied voltage raised to the five-halves power. The numerical value of the exponent of this power function, 2.5, is colloquially known as gamma.

If you actually read his document there is no way that you came away thinking his position was that the encoding should be the exact inverse of the display gamma in order to have an end-to-end gamma of 1.0, or that his position is that 2.2 is the correct gamma for displays, unless you didn't understand it. His position was made pretty clear in there that the end-to-end should be higher than 1.0 for video and that he thinks the CRTs like those used for mastering are higher than 2.2 for gamma.

--Darin

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post #92 of 395 Old 08-08-2009, 01:16 PM
 
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Just explaing to you and Poynton what actually being "encoded" thats all.

It' not Rec 709 now. Never was for almost 100% of the content being discussed here aka DVD/Blu ray release format. Darin and Chris, I can demonstrate the adjustments Poynton is talking about above. Can you or Darin?
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post #93 of 395 Old 08-08-2009, 01:19 PM
 
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Originally Posted by tbrunet View Post

http://www.poynton.com/PDFs/Rehabilitation_of_gamma.pdf

The Rec. 709 transfer function is standard for 525/59.94 and 625/60 conventional video, and for HDTV. The Rec. 709 function is based on a power function exponent of 0.45

...

Andrew should we redesign software and editing suite? So that a .51 model is the default perceptual model? Is .51 pre emphasis the same as a Rec 709 profile? .45 or .51 “average gamma” over the largest part of the defined dynamic range?

Geez Thomas. The Rec709 function has two parts, a linear portion, and then a portion that has an exponent of .45. However, taken together, the exponent of .45 by itself is not an accurate characterization of the curve because of the linear portion, and it comes closer to .5, as Andrew already described, and as Poynton describes in detail.

Rec 709 is not described by .45, even though it contains a portion with .45 as the exponent.

Quoting directly from Poynton(emphasis in original, brackets are mine):

Quote:


The Rec. 709 equation includes an exponent of 0.45. However, the effect of the scale factor and offset terms makes the overall power function very similar to a square root (YsubE ~ 0.5). For this reason, it is misleading to describe Rec. 709 as having "gamma of 0.45."

Rec. 709 encoding assumes that encoded R'G'B' signals will be converted to tristimulus values at a CRT (or some other display device) with a 2.5-power function (YsubD ~ 2.5).

...

The product of the effective 0.5 exponent at the camera and the 2.5 exponent at the display produces an end-to-end power of about 1.25, suitable for typical television display environment, as I explained in Rendering intent, on page 81. Should you wish to recover the RGB scene tristimulus values, invert Equation 23.2 [which is Rec 709]
...
Equation 23.4 [Rec 709 inversed] does not incorporate correction for rendering intent: The recovered values are proportional to the scene tristimulus values, not to the intended display tristimulus values. Rec 709 is misleading in its failure to discuss - or even mention - rendering intent. ...

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post #94 of 395 Old 08-08-2009, 01:20 PM
 
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Originally Posted by tbrunet View Post

Just explaing to you and Poynton what actually being "encoded" thats all.

It' not Rec 709 now. Never was for almost 100% of the content being discussed here aka DVD/Blu ray release format. Darin and Chris, I can demonstrate the adjustments Poynton is talking about above. Can you or Darin?

As I already said, we understand that, it is completely beside the point. It has little to do with the discussion. Can you please stick to one topic at a time? You claimed that Rec709 defined a display gamma of 2.2. It does not. That was a lie. Please stop spreading your misinformation about.
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post #95 of 395 Old 08-08-2009, 02:16 PM
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Originally Posted by tbrunet View Post

Andrew my question is why should we trust your interpretation if you don't comprehend the digital (color space) workflow.

When a digital editing platform linearize the Y'R-Y, B-Y luminance data for processing it's model and transform is based on a .45 gamma profile exactly. For nearly 100% of the data excursion (1-100 IRE)

The perceptual model is scaled so that a given camera's matrix profile will align with SMPTE/ITU-R Recommended Practice.

The Rec 709 profile crushes exposure latitudes I've have shown this to be a fact per Panavision's perspective anyway.

No one makes use of the standard default 709 gamma profile for motion pic releases, for real world cinema productions. One emulates a log gamma profile aka a filmlike look' within a Rec 709 space. The recording does not represent .51 unity Rec Camera default gamma conditions.

That Panavision document you linked to is all about image capture and why Panalog is better than the Rec. 709 curve at the camera.

I don't think anyone here has disputed that Rec. 709 is no longer used with modern camera systems.

It sounds to me almost like you think the only thing Rec. 709 describes is camera gamma. The word camera isn't even mentioned in it. Have you had a look over the paper?

You keep bringing up processes that happen before the data is encoded on the disc such as cameras and post-production that are irrelevant to this discussion, which is about display gamma. (and to a lesser extent, what is encoded on the disc as it relates to display gamma)

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Originally Posted by tbrunet View Post

DVD/Blu Ray disc have different recording gamma. Andrew I can explain how and more importantly 'why'.

Please do. If it's not BT.709 encoded on the disc, what is it and why?
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post #96 of 395 Old 08-08-2009, 02:32 PM
 
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Originally Posted by andrewfee View Post

Please do. If it's not BT.709 encoded on the disc, what is it and why?

Please read my postings in this thread again. I have validated the concept at least three times now.

Panavision defines said Rec 709 'camera' gamma. This average slope is .45 over 99% of it's transfer range.

It even appears Chris conceedes the reality of the facts? He says that “it’s" not as you have positioned here Andrew.
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post #97 of 395 Old 08-08-2009, 02:40 PM
 
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Thomas: Andrew and I are in agreement.

And I concede nothing to you thomas, I don't know where you got that from. You are, as usual, befuddled and misinformed.
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post #98 of 395 Old 08-08-2009, 02:51 PM
 
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Originally Posted by tbrunet
It' not Rec 709 now. Never was for almost 100% of the content being discussed here aka DVD/Blu ray release format.
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Originally Posted by ChrisWiggles View Post

As I already said, we understand that, it is completely beside the point. It has little to do with the discussion. Can you please stick to one topic at a time? You claimed that Rec709 defined a display gamma of 2.2. It does not. That was a lie. Please stop spreading your misinformation about.

You understand what exactly?
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post #99 of 395 Old 08-08-2009, 02:55 PM
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Originally Posted by tbrunet View Post

Just explaing to you and Poynton what actually being "encoded" thats all.

What you are doing is avoiding my question:
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Originally Posted by darinp2 View Post

You've quoted Poynton a lot. Do you disagree with him that the end-to-end gamma should be higher than 1.0 because people tend to prefer that? If the camera gamma is basically the inverse of 2.2 (the .45 you just posted) then it takes higher than 2.2 at the display to do what Poynton said. So, what is your position? Is it that the camera is the inverse of 2.2, the display is 2.2 and so the end-to-end is 1.0 and not the higher than 1.0 that Poynton claims?

It is pretty simple. Do you agree or disagree with Poynton on that point (or don't know)? I don't doubt that you'll take your usual tact of claiming that you already answered the question when you would have to be extremely ignorant to still believe what you posted. In this case:
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Originally Posted by tbrunet View Post

I quoted Poynton already in this thread and Mr. Poynton, Sony, Barco, HP and Microsoft all agreeing on the manufactured tolerances for CRT and the predictability of their phosphors basically make 2.2 @ D65 the target.

Seriously, are you so ignorant on the subject matter at this point, even after posting the paper where Poynton says why he doesn't think the display is 2.2, that you think Poynton's position is that 2.2 is the target for the display gamma? You claim you don't purposely mislead people. Prove it. Are you going to stick with your claim about what Poynton's position is or are you going to actually answer my question?

--Darin

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post #100 of 395 Old 08-08-2009, 03:03 PM
 
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Darin are you suggesting Dr. Soneira can not interpurt his own log-log data? He measured an average slope of 2.2 for the Sony CRT. No?

Does Dr. Soneira's data show a 2.4 Sony CRT response? Is his data invalid because the monitor was mis adjusted?
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post #101 of 395 Old 08-08-2009, 03:11 PM
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Quote:
Originally Posted by tbrunet View Post

Darin are you suggesting Dr. Soneira can not interpurt his own log-log data? He measured an average slope of 2.2 for the Sony CRT. No?

Does Dr. Soneira's data show a 2.4 Sony CRT response? Is his data invalid because the monitor was mis adjusted?

I already addressed those things. Dr. Soneira did not setup as things would be for mastering (I asked him this) and if you could do math you could calculate the gamma down at 10% and 20% from his own data, although I already did most of that for you. Do you need me to quote it again or disagree that the numbers on his figures are the numbers he provided? And his data doesn't change what Charles Poynton's position is. They can disagree and one of them can be wrong (or both can be), but it doesn't change what Charles Poynton's stated position is.

In Figure 1 and Figure 2 of his shootout the average slope is close to 2.2, but down low it is actually a little higher than 2.3. Overall a person could say 2.2 is the closest because it is from about 40% video level to 100% video level, but down low his own data doesn't match 2.2. But like I said, it doesn't answer what it would be as setup for mastering since according to Dr. Soneira he didn't set it up that way.

I also haven't seen Dr. Soneira weigh in on whether he thinks the end-to-end gamma should be higher than 1.0, exactly 1.0, or something else. He could believe the displays are 2.2, but that the end-to-end should be higher than 1.0. I don't know his opinion there.

You are still avoiding my question. Is it a difficult question for you to answer? You say that you don't purposely mislead people. I didn't ask you about Dr. Soneira's opinion. I asked you about Charles Poynton's opinion, as you have represented it a certain way that isn't true. Can you answer the question about whether you agree or disagree with Charles Poynton or not? If you disagree with him then just say so and don't try to avoid the question.

--Darin

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post #102 of 395 Old 08-08-2009, 03:17 PM
 
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OK..by accident that monitor measured exactly like I predicted it would. According to Ikegami they are designed to have a ruler flat response when nominally calibrated. Special custom gamma processing make this ideal response possible.

I guess the Dr. just got a malfunctioning Sony monitor that day, measured it and wrote that displaymate shootout article.
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post #103 of 395 Old 08-08-2009, 03:20 PM
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Originally Posted by tbrunet View Post

Please read my postings in this thread again. I have validated the concept at least three times now.

Panavision defines said Rec 709 'camera' gamma. This average slope is .45 over 99% of it's transfer range.

It even appears Chris conceedes the reality of the facts? He says that it's" not as you have positioned here Andrew.

Please stop talking about cameras. Cameras have nothing relevant to this discussion.


I had a look over the most recent Poynton PDF you posted. (I've read it before, but don't know it off the top of my head)

Quote:
Originally Posted by http://www.poynton.com/PDFs/Rehabilitation_of_gamma.pdf View Post

The CRT's power function is so similar to the inverse of the L* function that we make an engineering compromise: Instead of encoding Y using the L* transfer function, we encode RGB intensities to the inverse of the CRT's function. This allows us to dispense completely with transfer function circuitry at the display. We must then interchange the order of the matrix and the transfer function at the encoder. Changing the order of operations causes a departure from the Principle of constant luminance. In theory, the encoder would require a 0.4-power function.

This arrangement reproduces physical luminance correctly. However, it has a serious problem: The pictures do not look very good! When viewing a reproduced image, human viewers prefer a reproduction whose contrast ratio has been stretched slightly to a reproduction that is physically correct. The subjective preference depends somewhat upon the viewing environment. In effect, the visual system of the viewer imposes a power function with an exponent of about 1⁄1.25.

For television, a power function with an exponent of about 1.25 must be applied to overcome this effect, in order to produce images that are subjectively pleasing. Rather than introducing circuitry at the display to apply this function, we modify the transfer function at encoder. We use an exponent of about 0.5, instead of the physically-correct 0.4

Further on in the paper he states:
Quote:


I use the notation 0.5 as shorthand for the Rec. 709 function.


In addition, have another look over this graph that I posted:


2.2 gamma is not that similar to the L* curve. (but Rec. 709 with an end-to-end of 1.25 is)

I think I'm about ready to give up. Even the papers that you're referencing disagree with you.
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post #104 of 395 Old 08-08-2009, 03:27 PM
 
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Originally Posted by andrewfee View Post

Please stop talking about cameras. Cameras have nothing relevant to this discussion..

I've already quoted Poynton .. he states in black and white what you say here is false. Do I need to repeat what he said? about artistic intent of the colorist changing gamma? Which is done in the camera or post production processs.

It's (dynamic range) is directly coupled to the camera's recorded perceptual model.
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post #105 of 395 Old 08-08-2009, 03:31 PM
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Quote:
Originally Posted by tbrunet View Post

I've already quoted Poynton .. he states in black and white what you say here is false. Do I need to repeat what he said? about artistic intent of the colorist changing gamma? Which is done in the camera or post production processs.

It's (dynamic range) is directly coupled to the camear's recorded perceptual model.

Ok, that's it, I'm done.

If you don't see why cameras, or post-production are not relevant to this discussion, there's no point in continuing this any further.
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post #106 of 395 Old 08-08-2009, 03:36 PM
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Originally Posted by tbrunet View Post

OK..by accident that monitor measured exactly like I predicted it would. According to Ikegami they are designed to have a ruler flat response when nominally calibrated.

I guess the Dr. just got a malfunction Sony monitor that day, measured it and wrote that displayshoot article.

You are still avoiding the question. You claim you don't purposely mislead people, but here you are again with your usual tactics. Is what you claimed about what Charles Poynton's position true or false? Are you going to be a man for once, or keep avoiding it?

The disagreement between Dr. Soneira and Charles Poynton about the gamma numbers could be explained by the paper you yourself posted from Charles Poynton where he said, "The alleged wide variation comes from variation in offset term of the equation, not the exponent: Wide variation is due to failure to correctly set the black level."

Dr. Soneira told me in email that he did not setup either the white level or the black level of the display for mastering (but for a dark environment with white way up there) and Charles Poynton could say that the black level was set different than he felt was correct. I don't know if that is what he would say, but based on his article it would fit.

It is also amusing how you are now sticking with Dr. Soneira, a person who told you twice that you were wrong and was obviously not happy about you misrepresenting his position when he posted over 3 years ago now:

http://archive2.avsforum.com/avs-vb/...&&#post8121654
Quote:
Originally Posted by tbrunet View Post

I want to publicly thank you Dr. Soneira! You have validated my position on the direct correlation between CR ratio and Bit Depth. FWIW you are the only professional on this forum to do so!
Quote:
Originally Posted by Raymond Soneira View Post

First of all, I have not previously participated in this discussion, I certainly have not validated the above, and I strongly object to anyone using or invoking my name without my explicit permission.

Second of all, the above statement that the Contrast Ratio, CR, depends on bit depth is categorically wrong. CR is the ratio of Peak-Level Luminance to Black-Level Luminance. Those two special levels are absolutely independent of the Bit Depth, the Gamma Function, and the Transfer Function. Note, however, that all of the levels that lie between the Peak-Level and the Black-Level (17 to 234 for digital video or 1 to 254 for full range PC images and video) do explicitly depend on the Bit Depth, the Gamma Function, and the Transfer Function. Also, the digital levels near the Black-Level will be affected by the Contrast Ratio. I hope this clarifies my position. I consider the matter closed and will not be drawn into Ringer discussions of this type.

After he basically asked you not to misrepresent his opinion and after the owner of this forum even asked you basically the same thing you spent the next couple of years or so misrepresenting one of Dr. Soneira's opinions since he wasn't going to play your game and keep correcting you here, and now here you are using him again as proof that you are right. You did that before about stuff you were obviously wrong about, which is interesting because before you were using that section of his article to say that things were linear and so you were right about 219:1 being the highest on/off CR possible and now you are using basically the same section to claim that things aren't linear, but follow a 2.2 gamma curve. I know you spent more than a year with your "linear" game from that one section even after I had explained it to you (linear on a log-log graph is not the same as linear in linear space), so how did you magically come to understand it and take it as gospel that CRTs have 2.2 gamma as setup for mastering?

To be clear, maybe they are 2.2, but tbrunet is not a trustworthy person on things like this. He has shown how he will claim the most incredibly ignorant stuff from a person in the industry and after it is explained he will try to continue convincing people to believe the dumbest things (like his stuff about it being impossible for on/off CR to be higher than 219:1 or 1000:1).

Here tbrunet could be a man about what Charles Poynton's stated position is, but I don't expect tbrunet to all of a sudden show himself to be intellectually honest after what he has proven about what he will do over the last almost 4 years.

tbrunet will grasp onto pretty much any industry expert he can. Since they aren't here he can misrepresent their position, like he did with Dr. Soneira over and over.

--Darin

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post #107 of 395 Old 08-08-2009, 03:39 PM
 
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Histronics mode again huh Darin?

Thanks!..you're a true pal for sure.


Regards,

thomas
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Avoiding all of Darin's questions again Thomas?

I think what's most hilarious is that you're in here trying to explain to us what gamma is, when you are of the belief that if 100% stim gives you 10fL then 50% stim gives you 5fL. THAT is what's really freaking funny. And you're sitting here "explaining" what gamma is. What a joke.
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post #109 of 395 Old 08-08-2009, 03:46 PM
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Quote:
Originally Posted by tbrunet View Post

Histronics mode again huh Darin?

Thanks!..you're a true pal for sure.

I'm not going to apologize for pointing out when you are acting without integrity. You could choose to be a man at any point.

You and I both know how low your claims that you have 30 years of experience and so people should trust you are given some of the things you have claimed here after you had 25 years of experience and some of the really low games you have played to try get people to believe you weren't wrong.

Being wrong isn't the reason you deserve it. Your low behavior is. We are all wrong at some point, but people have a choice to take the low path you choose or to have some integrity in that case.

Many people were willing to help you out if you showed integrity.

You can be mad at me for pointing out the actual history, but you and I both know what I posted is true (and is backed up by actual posts that you no longer have the ability to remove).

--Darin

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post #110 of 395 Old 08-08-2009, 03:52 PM
 
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Originally Posted by darinp2 View Post

You can be mad at me for pointing out the actual history, but you and I both know what I posted is true (and is backed up by actual posts that you no longer have the ability to remove).

You do not understand gamma..nor am I convienced you comprehend a normalized video signal.

Have a nice day
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post #111 of 395 Old 08-08-2009, 04:01 PM
 
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Originally Posted by ChrisWiggles View Post

Avoiding all of Darin's questions again Thomas?

I think what's most hilarious is that you're in here trying to explain to us what gamma is, when you are of the belief that if 100% stim gives you 10fL then 50% stim gives you 5fL. THAT is what's really freaking funny. And you're sitting here "explaining" what gamma is. What a joke.

Yes and I even explaind how voltage (encoded pre emphasis) is embedded in the digital payload. It's strictly based on a normalized voltage model.

Name any color difference code Y'CbCr values and I can tell you the exact voltage being encoded per SMPTE/ITU-R protocol.
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post #112 of 395 Old 08-08-2009, 04:04 PM
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Quote:
Originally Posted by tbrunet View Post

You do not understand gamma..

You seem to like to prove me right. It is always funny when you use this "You don't understand ..." after you have posted the most ignorant stuff about the subject matter you are claiming I don't understand. You probably think your statement actually means something, but coming from a person who avoided my question about how bright 10% video level should be relative to 100% video level for a year or more and then 2 years ago finally answered it and showed they didn't understand gamma given that they thought that a 10% video level would be 1 ft-lambert if 100% video level was 10 ft-lamberts, as is shown in your answer here:

http://www.avsforum.com/avs-vb/showt...3#post11010633
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Originally Posted by tbrunet View Post

Y = .1 or 10IRE
L* = 37.842
Density = 1 or (10:1 contrast) or (log 10)
10 / 10 = 1 ft lambert

it doesn't mean a whole lot. Kind of like being told I don't understand calculus by somebody who thought 9 times 9 was 18. If I don't understand gamma then why did you get the answer wrong and I had to explain it to you so that years later you could finally come up with a reasonable answer to my question?

Heck, even a year ago here:

http://www.avsforum.com/avs-vb/showt...7#post14413117

you supported that gamma didn't apply to digital, only analog, where you backed up DefinerOfReality's position that if 100% video level was 10 ft-lamberts then 50% video level would be 5 ft-lamberts because gamma doesn't apply to digital by saying it was a good point. The funny thing is that he also claimed over 20 years of experience in the industry and between the 2 of you you couldn't even come close to what a person with a week's experience and a meter could figure out in a short amount of time.

Do you even realize how clear it is that you are just trying to avoid my question about whether you agree or disagree with Poynton?

--Darin

This is the AV Science Forum. Please don't be gullible and please do remember the saying, "Fool me once, shame on you. Fool me twice, shame on me."
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post #113 of 395 Old 08-08-2009, 04:15 PM
 
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Digital code words;

126,128,128

.35V,0V,0V

Y'CbCr

Is that a linear correlation or non linear?

I corrected it ..and yes it's linear
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post #114 of 395 Old 08-08-2009, 04:17 PM
 
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Quote:
Originally Posted by tbrunet View Post

I'll give you a clue here Chris:

8 bit digital code word 126,128,128 results in:


.5V,OV,0V

normalized .7V p-p Y' and +/- .350mV CbCr smpte standard video signal.

Is that not a linear relationship?

Uh, for .7v that would actually give you 350mV, not 500mV. And yes that is a linear relationship.
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post #115 of 395 Old 08-08-2009, 04:19 PM
 
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So if your above example gave you 2fL on a display, what would 235, 128, 128 (700mv)give you?
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post #116 of 395 Old 08-08-2009, 04:20 PM
 
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Quote:


Digital code words;

126,128,128

.35V,0V,0V

Y'CbCr

Is that a linear correlation or non linear?

I corrected it ..and yes it's linear
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post #117 of 395 Old 08-08-2009, 04:21 PM
 
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Okay, fine I see that you corrected it, answer my question.

So if your above example gave you 2fL on a display, what would 235, 128, 128 (700mv)give you?
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post #118 of 395 Old 08-08-2009, 04:22 PM
 
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Volts and IRE luminance as encoded on a DVD is linear. Deal with it.
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post #119 of 395 Old 08-08-2009, 04:24 PM
 
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Originally Posted by tbrunet View Post

Volts and IRE luminance as encoded on a DVD is linear. Deal with it.

Volts and digital values are linear to each other, they always have been, this isn't news to anyone. That's not my question. Answer my question:

If your above example (350mv) gave you 2fL on a display, what would 235, 128, 128 (700mv)give you?
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post #120 of 395 Old 08-08-2009, 04:32 PM
 
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Chris in the past you've suggested one could not encode volts in the digital domain.

When you play a given DVD or Blu ray disc this baked in 'look' is propogated as I've described above inside the payload.
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