Latest post Tue, Nov 27 2012 2:35 AM by Martin in Chicago. 10 replies.
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  • Mon, Nov 12 2012 8:39 PM

    Why so dark?

    A while ago I linked to a lot of AMA files and transcoded them to DNxHD 115. I believe the footage was captured on a Canon 5D and a 7D. Today, I looked at them and decided they looked crushed in the blacks and blown out in the whites. I went back to the original H.264 files and they look fine. So I transcoded one original clip again, compared it and this time it looks fine.

    What could I have done to create this inconsistancy; I definitely don't want to make this mistake again. Both transcodes were done in the same project with, I bleieve, the same settings. 

    MC 2018.11.0, OS 10.13.6, Early 2009 Nehalem MacPro4,1, 2 X 2.6 GHz Quad-Core updated with Samsung 850 EVO 1 TB system drive, 32 GB RAM and ATI Radeon... [view my complete system specs]
  • Mon, Nov 12 2012 8:51 PM In reply to

    • Marty
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    Re: Why so dark?

    Maybe a different MC Version? I had problems with MC6: http://community.avid.com/forums/t/114500.aspx

    Perian (Quicktime codec) can also make trouble if it's activated. 

    And you could edit the Source Settings of the AMA clip to "Expand video levels" or "Compress graphic levels".

    all different setups in various editing suites. my own: MC 2018.2, OSX 10.12.6, iMac (Retina 5K, 27-inch, 2017), 4,2 GHz Intel Core i7, 40GB RAM, Radeon... [view my complete system specs]

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  • Mon, Nov 12 2012 9:08 PM In reply to

    Re: Why so dark?

    Bloersch:

    Maybe a different MC Version? I had problems with MC6: http://community.avid.com/forums/t/114500.aspx

    I'll look that over, Marty, but I've been using the same version (5.5.3) the entire time.

    Bloersch:

    Perian (Quicktime codec) can also make trouble if it's activated. 

    Yeah, that occured to me so I mounted Perian earlier today and tried a transcode to see if the clip came out dark. It didn't. I can't swear Perian wasn't installed when I did the original transcodes, but it doesn't seem to be causing the problem.

    Bloersch:

    And you could edit the Source Settings of the AMA clip to "Expand video levels" or "Compress graphic levels".

    I'm sorry, I don't follow this at all (and can't find those phrases in the manual). Is this something new to 6?

    MC 2018.11.0, OS 10.13.6, Early 2009 Nehalem MacPro4,1, 2 X 2.6 GHz Quad-Core updated with Samsung 850 EVO 1 TB system drive, 32 GB RAM and ATI Radeon... [view my complete system specs]
  • Mon, Nov 12 2012 9:34 PM In reply to

    Re: Why so dark?

    With AMA linked clips you need to use the "set Source Setting" option to look at the historgram and see how the contrast range fits with the two 2hite marker lines (for 16-235) then decide if the levels need exapnding, contracting or as they are.

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  • Mon, Nov 12 2012 9:57 PM In reply to

    Re: Why so dark?

    Pat,

    I'm not remotely afraid to expose my ignorance, but I am always concerned about testing the patience of those who would help a stranger. Still, I'm just not getting it. I have now, for the first time, found "set Source Setting" in the RED section of the manual, but I'm not clear how this applies. I'm not cutting with the AMA clips; I transcoded them. The original clips look fine; the transcoded are off.

    Is the idea that I blow out the AMA clips so the trancoded ones look normal? That wouldn't work retroactively anyway, would it?

    MC 2018.11.0, OS 10.13.6, Early 2009 Nehalem MacPro4,1, 2 X 2.6 GHz Quad-Core updated with Samsung 850 EVO 1 TB system drive, 32 GB RAM and ATI Radeon... [view my complete system specs]
  • Mon, Nov 12 2012 10:03 PM In reply to

    Re: Why so dark?

    I can tell you from now fiddling with the "set Source Setting" window, that if I "expand video levels to graphic levels" on an AMA clip, it looks like what I'm getting post-transcode. Does that tell me anything?

    MC 2018.11.0, OS 10.13.6, Early 2009 Nehalem MacPro4,1, 2 X 2.6 GHz Quad-Core updated with Samsung 850 EVO 1 TB system drive, 32 GB RAM and ATI Radeon... [view my complete system specs]
  • Mon, Nov 12 2012 10:21 PM In reply to

    Re: Why so dark?

    It's very rare for me to have to work with content (in terms of final delivery) that isn't studio levels (ie black at 16 or above and white at 235 or lower)

    But I do get a lot of full swing level source files and they often go from 0-255 in terms of levels so they always look contrasty and "nice" when viewed but on my scopes show to be going sub black and super white.

    So just looking at the files isn't a valid measure I need to use the scopes (eitehr in MC via the CC tool or better still on external scopes)

    My final finished programme is then 16-235 levels and either laid to tape like that or exported like that. If I need to make a "vieweing file" then I'll expand those levels back out to 0-255

    So when I originally AMA link files (or import them) I have to check that I end up with the levels at 16-235. I care less that they look low contrast. That's how they have to look to be correct. It all comes right at the end.

    ACI Moderator. I'm not employed by Avid or work for them. I just do this in my spare time. Normally using the current Media Composer version on My... [view my complete system specs]

     

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    QC/QAR Training - Understanding Digital Media - Advanced Files * Compression - Avid Ingest - PSE fixing courses and more

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  • Mon, Nov 12 2012 10:38 PM In reply to

    Re: Why so dark?

    I tend to get wordy, Pat, and so I try to self edit. I have checked these clips against Avid's internal scopes and before transcoding, the levels range from 16-235. After trancode the range hits the bottom and top bars, meaning well beyond 16-235 on either end.

    MC 2018.11.0, OS 10.13.6, Early 2009 Nehalem MacPro4,1, 2 X 2.6 GHz Quad-Core updated with Samsung 850 EVO 1 TB system drive, 32 GB RAM and ATI Radeon... [view my complete system specs]
  • Wed, Nov 14 2012 5:19 PM In reply to

    Re: Why so dark?

    Martin in Chicago:

    A while ago I linked to a lot of AMA files and transcoded them to DNxHD 115. I believe the footage was captured on a Canon 5D and a 7D. Today, I looked at them and decided they looked crushed in the blacks and blown out in the whites. I went back to the original H.264 files and they look fine. So I transcoded one original clip again, compared it and this time it looks fine.

    What could I have done to create this inconsistancy; I definitely don't want to make this mistake again. Both transcodes were done in the same project with, I bleieve, the same settings. 

    The problem is Quicktime. It wants to make everything display nicely on your computer screen. But it plays havoc with Avid because Avid does not set the black and white points to conform to computer graphics (0-255), but rather to conform to 709 specs (16-235). The advantage is headroom for blacker than black and whiter than white. But Quicktime likes to play in RGB because that is what your computer displays. It is entirely possible for one day to have exactly the problem you describe and then another day it all looks OK. 

    Since somone mentioned Perian, I just did a little test. I looked at some 5D footage AMA linked without Perian and it was fine with the source settings untouched. I transcoded it so I could see if there would be any change with what I tried next. I then quite MC and installed Perian. Launch MC and looked at the same AMA clip - blacks were crushed. Changing source settings to remap RGB black and white points to 709 brought it into range, but it was still dark. With neither setting did it match the transcoded (with correct levels) clip that was created with Perian uninstalled. The blacks required a small curve to make them closer to normal. I then quit MC, uninstalled Perian and everything was normal again. Perian installs a system preference where you can easily install and uninstall with a mouse click and not reboot. 

    Perian's purpose is to be able to play any video on your computer by installing lots of codecs for quicktime to choose from. THAT is a problem. When I was working at CBC last year, I wondered why they limit the number of codecs on their Avid systems. Now I know. 

    I suspect there is other codec software that might mess wth Avid as well. The only way to be sure is to have a reference clip that you can examine before and after installation of other codecs. 

    I hope this helps. 

    Dennis

     

  • Wed, Nov 14 2012 8:18 PM In reply to

    Re: Why so dark?

    Well, that sort of helps, Dennis. And it was absolutely informative. But here's what still not resolved for me. My AMA linked files look just fine and always have. If (and I know this is not a terribly precise test) I open an original file in QT and float it over the same clip AMA-linked in the Composer window I can see no difference. It's in the transcoding that my stuff is turning dark. And then only some of the time. It sounds to me like you're saying the issue would occur at AMA linking and not at transcoding.

    I cannot say with absolute certainty that when I did the transcoding originally I had Perian uninstalled (I regularly take advantage of Perian's easy install/uninstall in System preferences, which means I sometimes forget to check it). But I did, yesterday or the day before, attempt to transcode both with it installed and with it uninstalled and in both cases the transcodes looked like the original files.

    And, if it's helpful, I can tell you Avid identifies the original AMA-linked file as having a color space of YCbCr 601 and the transcoded ones, both the dark one and the normal one of YCbCr 709,

    OK, so full disclosure time. (I left this part out of my original entry because it wasn't relevant to my most immediate questions, e.g. why did this happen and how do I keep from doing it in the future.) I hadn't simply linked and transcoded. For 308 clips, I'd linked, transcoded, synced two two-channel audio recorders to each clip, renamed clips, multiclipped A camera with B camera for about a third of the shoot, did some organizing, lined them all into a script and finally started editing (OK, I also didn't include this because I was a little embarassed by how late in the game I was double checking this issue).

    I intended on treating these clips as the masters and never reverting back to the originals or re-transcoding to a higher resoluttion. I've never had to attempt a link to original or reimport of a sequence with multiclipping so I'm concerned that all that work was for naught.

    But now I'm just cluttering the conversation.

    MC 2018.11.0, OS 10.13.6, Early 2009 Nehalem MacPro4,1, 2 X 2.6 GHz Quad-Core updated with Samsung 850 EVO 1 TB system drive, 32 GB RAM and ATI Radeon... [view my complete system specs]
  • Tue, Nov 27 2012 2:35 AM In reply to

    Re: Why so dark?

    Alright, not to belabor the point —and maybe I should make this a new thread, but I have no idea how to get back to the original image quality on this sequence. To refresh, I realized only after a substantial amount of work, that my transcoded clips were substantially more pushed to both the whites and blacks than the original AMA clips. I have since tried to again transcode some of the same clips and they come out fine: just like the originals.

    But I just now tried to decompose and reimport a portion of my sequence to to see if I could get it to match in exposure the originals. Oddly —and I tried this twice— I'm getting clips less crushed, but still not the same as the original. I'm still cutting, but eventually I'm going to need to color correct and I'd like to do it from a sequence that has the original image quality. How do I do this?

    Here are frame grabs comparing (in order from best to worst) the original H.264 file, today's decompose, the initial transcode and then their respective waveforms.

    Any help would, as always, be greatly appreciated.

    MC 2018.11.0, OS 10.13.6, Early 2009 Nehalem MacPro4,1, 2 X 2.6 GHz Quad-Core updated with Samsung 850 EVO 1 TB system drive, 32 GB RAM and ATI Radeon... [view my complete system specs]
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