ARRI DigitalGeneral CategoryTechnicalKodak TAF film 45% video Level help!!!
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mykg24
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« on: May 03, 2012, 06:57:33 PM »

I was hoping someone could explain something to me, in Kodak TAF film, the negative LAD patches are calibrated to a video level near 45%. I was wondering why they are calibrated to 45%, what that 45% means, and how do you calculate that?

I know that 45% has to do with Video and IRE, but I don't know why and where to look for background information for it.

Thank you to whoever can help me, it would be greatly appreciated!
« Last Edit: May 03, 2012, 07:03:11 PM by mykg24 » Logged

Michael Borenstein
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« Reply #1 on: May 03, 2012, 07:38:53 PM »

Hello Mykg24.

the LAD patch for the TAF film is actually used to calibrate a telecine to be used as a starting point for film reproduction as a reference for Dmax/Dmin and middle grey (LAD) as well as to setup the blacks, whites, grays and saturation levels. 

The LAD patch itself should correlate to 39 IRE (Composite) and 45 IRE for (Component).

What you might be referring to is that a grey card, according to the Kodak TAF White Paper, should correspond to 45 IRE ,which serves as a starting point for colorists to set up their grades and take the guess work out of how the sceen was/is suppose to look, ie white is 80 IRE, Black is 20, and Grey is 45 IRE.

And of course, as I'm sure you know, all of these IRE's correspond directly to a mV value for a CRT monitor in order to reproduce color and luminance in a repeatable and precise manner.

Hope this helps.  All this info can be found here:  Link.

Another invaluable reference:  Quantel Digital Fact Book

Regards
Mike
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Michael Borenstein
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mykg24
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« Reply #2 on: May 03, 2012, 08:00:59 PM »

Hi Thank you so much for replying so fast! Right the greycard is what I am referring to, but I don't understand why 45% was chosen. I understand that 45% was chosen to serves as a starting point for colorists, but why not 50% or 40%. Why mathematically did Kodak chose 45%?
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Michael Borenstein
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« Reply #3 on: May 04, 2012, 05:06:22 AM »


Because step 8 (Full White/DMAX) equals .7mv and 100 IRE.
LAD (Middle Grey/Grey Card) equals .32mV, which is 45% of the scale.

That's where the 45 comes from.
Regards
Mike
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Michael Borenstein
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mykg24
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« Reply #4 on: May 04, 2012, 05:32:37 AM »

oh wow thank you so much! How Kodak calculated that 45% was killing me!
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Michael Borenstein
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« Reply #5 on: May 04, 2012, 05:52:30 AM »

No problem.

Regards
Mike
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Michael Borenstein
Digital Service Manager, Arri Inc.

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