Video Calibration Q&A - Page 5 - Home Theater Forum and Systems - HomeTheaterShack.com

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post #41 of 77 Old 01-05-10, 06:01 PM
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Re: Video Calibration Q&A

Pretty good steering of a topic there Bill. I even caught a hint of some statistics about to creep in. I wonder why?




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post #42 of 77 Old 01-05-10, 07:09 PM
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Re: Video Calibration Q&A

I see... I misinterpreted what you were saying from get-go.... typical
So one last thought.... "features" like CMS controls, or gamma controls, different firmware? Or more expensive chips? (Let's not differentiate between good/bad full3D/2D CMS or 10-point gamma sliders...)

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post #43 of 77 Old 01-05-10, 07:25 PM Thread Starter
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Re: Video Calibration Q&A

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I see... I misinterpreted what you were saying from get-go.... typical
No worries. It's a good thing I keep this thread subscribed, otherwise it might be months before I remember to check back in on it (seems like a flurry of activity, and then dormant...).

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So one last thought.... "features" like CMS controls, or gamma controls, different firmware? Or more expensive chips? (Let's not differentiate between good/bad full3D/2D CMS or 10-point gamma sliders...)
Definitely more expensive chips and more of them. The math isn't hard, but it is more math. Where it gets maddeningly complex is translating the matrix real-number math into integer math. In theory, if you put the CMS right at the point where you convert the inbound signal into linear RGB (i.e., at the RGB LUT), then you just need to do a relatively simple transform. People who talk about a CMS not being fully-featured because it doesn't include independent adjustments for secondaries that is different than the primaries, among other things, don't actually know how color math works. When you move the CMS from this "sweet spot", you end up adding complexity and cost into the design.

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post #44 of 77 Old 01-05-10, 07:44 PM
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Re: Video Calibration Q&A

Thr sweetness of that spot also depends on assumptions about what it takes to get "linear" RGB. Add to that characteristics of the display that may require some additional consideration for spectral densities that are not consistent with the approximations on the camera and encoding side, or primary limitations, or extra color wheel segments, or having to modulate panel response in various ways, or frame rate interactions with display latencies or a dozen other variables and we end up with non-trivial challenges. But then, that is why we need tools like CalMAN, right?




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post #45 of 77 Old 01-05-10, 08:55 PM Thread Starter
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Re: Video Calibration Q&A

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Thr sweetness of that spot also depends on assumptions about what it takes to get "linear" RGB. Add to that characteristics of the display that may require some additional consideration for spectral densities that are not consistent with the approximations on the camera and encoding side, or primary limitations, or extra color wheel segments, or having to modulate panel response in various ways, or frame rate interactions with display latencies or a dozen other variables and we end up with non-trivial challenges. But then, that is why we need tools like CalMAN, right?
So that we are clear, the conversion from R'G'B' or YCbCr to linear RGB is very straight-forward. You do have to make an assumption (or have an explicit control) for gamma, but that's really it. To your point, how the signal is then translated into physical light is definitely dependent upon display-specific factors.

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post #46 of 77 Old 01-05-10, 09:07 PM
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Re: Video Calibration Q&A

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No worries. It's a good thing I keep this thread subscribed, otherwise it might be months before I remember to check back in on it (seems like a flurry of activity, and then dormant...).
I have the opposite problem, I subscribe to so many just to make sure I don't miss anything important that it takes me over 2 hrs a day just to browse most and read the few that I find interesting...
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Definitely more expensive chips and more of them.
ARG. But THAT means increased BOM cost! (Sorry, I just couldn't resist)
Seriously though, I do see your points.
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People who talk about a CMS not being fully-featured because it doesn't include independent adjustments for secondaries that is different than the primaries, among other things, don't actually know how color math works.
I wasn't going to get to this for a few months, but since you mention it...
Why is it that people sometimes report that their secondaries don't fall on the line between their primaries? Or for that matter report secondary luminances that aren't the sum of the primary luminances? (that IS the correct math, isn't it?) Is this simply a bad LUT or improper calcuations or something more, er, sinister?

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Thr sweetness of that spot also depends on assumptions about what it takes to get "linear" RGB. Add to that characteristics of the display that may require some additional consideration for spectral densities that are not consistent with the approximations on the camera and encoding side, or primary limitations, or extra color wheel segments, or having to modulate panel response in various ways, or frame rate interactions with display latencies or a dozen other variables and we end up with non-trivial challenges. But then, that is why we need tools like CalMAN, right?
Nice Len.<insert-shameless-plug-here> And you don't even work for them... (do you?)

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post #47 of 77 Old 01-05-10, 09:20 PM Thread Starter
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Re: Video Calibration Q&A

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I wasn't going to get to this for a few months, but since you mention it...
Why is it that people sometimes report that their secondaries don't fall on the line between their primaries? Or for that matter report secondary luminances that aren't the sum of the primary luminances? (that IS the correct math, isn't it?) Is this simply a bad LUT or improper calcuations or something more, er, sinister?
Some of it could be bad information floating around. I have some issues with a certain often-quoted "guide" on another forum. Also, it could be misunderstanding of good information. Or it could be bad tools. Or ...

In other words, it is probably some combination of all of these issues. For a display that is worth calibrating, I doubt it is the display itself unless someone has just really screwed something up in a menu in which they didn't belong.

For example, unless someone finds a way around Grassman's law, the sum of the luminances of each primary is most assuredly equal to the total luminance.
http://en.wikipedia.org/wiki/Grassma...w_%28optics%29

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post #48 of 77 Old 01-05-10, 09:32 PM
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Re: Video Calibration Q&A

That's a shame. I've studied well the guide of which you've spoken.

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post #49 of 77 Old 01-05-10, 10:01 PM
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Re: Video Calibration Q&A

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So that we are clear, the conversion from R'G'B' or YCbCr to linear RGB is very straight-forward. You do have to make an assumption (or have an explicit control) for gamma, but that's really it. To your point, how the signal is then translated into physical light is definitely dependent upon display-specific factors.
Yes, of course, the conversion is easy linear math. It is the assumption about gamma that is not so straightforward. Encode gamma can vary a great deal. There is no way for the display to know what it was, so the linearity is really an approximation. The error may not matter much, but in some cases can be significant. This is one reason that sources vary so much and the education of the user with regard to how to use controls even on a calibrated display is so important. It is also a reason that a properly calibrated display is essential. At least you have a starting point in the calibrated settings, which takes out much of the most objectionable variance in the results.




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post #50 of 77 Old 01-06-10, 08:01 AM
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Re: Video Calibration Q&A

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Encode gamma can vary a great deal.
And here I thought all along that at least the movie studios stuck to the 0.45 encode... at least from what's "seen" on the monitor to the signal...

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