Latest post Sat, Apr 16 2016 11:17 AM by David Yardley. 1 replies.
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  • Thu, Apr 14 2016 8:36 AM

    • S.Clements
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    Avid Shifting Quicktime Gamma or Levels - not shifted in Premiere, Mpeg Streamclip or QT player


         I have a file that Avid is shifting the gamma on (or doing some similar levels conversion).  The quicktime is in the format libquicktime (which I am not familiar with).  The video appears to have proper black levels when played in Quicktime player or in Mpeg Streamclip, however the moment it is either imported or AMA linked to Avid, the image instantly goes very noticeably milky.  When it is exported from Avid, it is still milky.  I did tests where I imported other quicktime clips and they didn't have the same issue.

         I was able to fix the issue by converting the quicktime to be an Avid DNxHD115 quicktime with Mpeg Streamclip, before I brought it into Avid.  In this way, the color levels were maintained and Avid didn't shift them.  

        It's almost as  though there were some sort of LUT or something attached to the quicktime and Avid threw it away, but other programs held onto it.  When I took the original quicktime into Premiere, everything was fine - no shift.

         Does anyone know whats going on?  Having to convert in Mpeg Streamclip before ingesting into the Avid is very time consuming - especially with multiple files.

        I tried AMA linking and changing the source settings.  I know the original footage was shot on Alexa, but switching to Alexa levels doesn't help - all the black levels and colours look wrong.  The file was worked on and prepped by a different company before coming to us.

       Any suggestions on how to make Avid not alter the gamma or levels ?

    Avid Media Composer 8.3.1 Macbook Pro (Retina, 15-inch, Mid 2014) 2.8 GHz Intel Core i7, 16GB Ram Mac, OS 10.10.2 [view my complete system specs]
  • Sat, Apr 16 2016 11:17 AM In reply to

    Re: Avid Shifting Quicktime Gamma or Levels - not shifted in Premiere, Mpeg Streamclip or QT player


    My experience is that AMA linking and inporting into MC does not alter levels or Gamma, as long as you steer clear of adding any kind of lut or other modifying actions.

    Alexa Prores 444 will look flatter in MC post MC7.02 than in QT, Assimilate Scratch, Resolve etc. as these add a legal to full swing change, indeed this is why the Alexa always produces legal Prores 444 QT's. (this undocumented change in MC frustrated me for nearly a year, as I thought MC post 7.02 was handing it wrongly.)

    Arri say this:

    Apple specifies that ProRes should be legal range. Our tests have shown that an extended range ProRes file can result in clipping in some Apple programs. However, the difference between legal and extended coding are essentially academic, and will not have any effect on any real world images. An image encoded in 10 bit legal range has a code value range from 64 to 940 (876 code values), and a 10 bit extended range signal has a code value range from 4 to 1019 (1015 code values). Contrary to popular belief, extended range encoding does not provide a higher dynamic range. It is only the quantization (the number of lightness steps between the darkest and brightest image parts) that is increased by a marginal amount (about 0.2 bits).

    It is probable that MC is showing the levels correctly and the other software is showing it wrongly. If you export SAS without transcoding to another codec inside MC you should find that the footage will "match" the original even in QT etc.

    Symphony 7.06 OS 10.9.5 QT 7.6.3 Mac Pro 2x2.66 6-core 32GB Ram Aja Kona 3. MC 7.0.6 OS 10.9.5 Mac Pro 5.1 2x2.97 6-core 14GB ram Aja I/O express, Apple... [view my complete system specs]
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