Alexa Metadata for VFX

Tue Aug 16, 2016 4:41 pm

Hi,
I'm trying to build a tool to automatically extract VFX relevant metadata for our artists through Nuke and I'm running into some problems, I'll try to break them down into points for better clarification.

- As mentioned in another topic here, sometimes i find the <Lens Iris> value is 0.707107 and <Lens Linear Iris> is 0. What does that mean? I have read the Metadata whitepaper and believe i understood the conversion part. Basically if the Linear Iris for example is 10003 that would mean a T-Stop of 22.
I still cant figure out what to make of the 0.707107 value.

- The <Lens Linear Iris> although available when using Arri Meta Extract, It never shows up in Nuke Studio or Nuke's metadata. Even when the source is ARRIRAW. I always thought metadata being excluded in Nuke was only a problem with quicktime files.

- Is working with the LogC2Video_Rec LUT from the LUT generator a correct workflow for artists on a sRGB monitor? Doesnt it assume a gamma2.4 monitor?

I have a attached a CSV file showing the Lens Iris issue.

Thanks
Mohamed Selim
 
Posts: 7
Joined: Tue Aug 16, 2016 12:48 am

Re: Alexa Metadata for VFX

Wed Aug 17, 2016 2:24 pm

Dear Mohamed,

prior to using a LDS lens it has to be initialized. Usually this is a quick process where you turn the lens-rings for each of the two (or three): focus, iris (and zoom). An un-initialised lens connection or a not properly initialized lens produce the "0.7xx"-value.

Not being a NUKE expert, I asked my colleagues:

Lens Linear Iris
Should show up in the metadata panel of the read-node for ARRIRAW and/or Open EXR rendered with ARC 3.4. We do not have a library for dpx yet, but are working on it.

LogC2Video_Rec LUT
That's the LUT we use as well; make sure your monitor is calibrated for REC 709. We calibrate to REC 709, 80cd/m2, 6500 Kelvin and gamma 2.4.
Jan Heugel
Application Engineer
Jan Heugel
 
Posts: 225
Joined: Wed Aug 13, 2014 3:15 pm
Location: Munich, Germany

Re: Alexa Metadata for VFX

Wed Aug 17, 2016 3:58 pm

Thanks Jan. I will check out the difference in output between ARC and Nuke Studio.

As for the LUT, I think this works for Broadcast monitors calibrated to Rec709 which have a gamma of 2.4. All the artists here have normal consumer sRGB monitors calibrated to sRGB gamma 2.2.

Thanks
Mohamed Selim
 
Posts: 7
Joined: Tue Aug 16, 2016 12:48 am

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