Latest post Tue, Jul 13 2010 6:36 PM by editz. 13 replies.
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  • Mon, Apr 6 2009 10:54 PM

    • editz
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    HD to SD export causes black level shift?

    There are a ton of variables here, but I'll just lay them out and maybe somebody can make sense of it.

    Two rigs, one MCAHD 2.6.1 and the other MCSoft 2.7.2.  Both using Quicktime 7.6 (which I think might be a culprit).  Editing in HD, they export test clips.  First Avid exports DNxHD 1920x1080 and Meridien Compressed 720x486.  Second Avid exports Animation 1920x1080 and Meridien Compressed 720x486.  File Field Order is Even and they swear everything is set to 601.

    I import all clips to my 2.2.10 rig (which runs Quicktime 7.1) trying out all Aspect Ratio/Pixel Aspect options and all at 601 levels.  Black levels on all SD clips are elevated.  HD clips look good.

    The other oddity is that all clips from the first Avid have a fuzzy bottom edge and a sharp top on their "letterbox" and the exact opposite from the other one.

    For the heck of it, I exported a clip off my rig and it came back in with levels unchanged, so I'm fairly confident it's not something on my end.

    Due to space it would be preferable for these two rigs to output SD .mov files to send across a network (different cities) where I can import them and lay off to Digibeta.  I cannot figure out why the blacks are elevated when they attempt to downconvert.  Is this a known issue?  It smells like a 601/RGB mismatch someplace to me.

     

  • Mon, Apr 6 2009 11:01 PM In reply to

    • gumbaedit
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    Re: HD to SD export causes black level shift?

    We just had this problem on my show, but it's really not that big of a problem, or one at all depending on your workflow.  There are a couple of threads about it in the forum archives.  My main question is this, are you outputting thru mojo sdi to SD, and is your system capable of using the HD media?  If so, then I have a solution for you.

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  • Tue, Apr 7 2009 5:33 AM In reply to

    • luca.mg
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    Re: HD to SD export causes black level shift?

    Click HERE for a thread that may be interesting regarding QT export.

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    peace luca

  • Tue, Apr 7 2009 5:01 PM In reply to

    • editz
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    Re: HD to SD export causes black level shift?

    gumbaedit:
    are you outputting thru mojo sdi to SD, and is your system capable of using the HD media?  If so, then I have a solution for you.

    No, my rig has the Adrenaline DNA box and we're going out SDI to digibeta.  Strictly SD.

     

  • Tue, Apr 7 2009 5:10 PM In reply to

    • editz
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    Re: HD to SD export causes black level shift?

    luca.mg:

    Click HERE for a thread that may be interesting regarding QT export.

    I read that thread and I think it has more to do with exporting QTRef files and the Use Avid DV codec option.  We're outputting full QT files in Meridien Compressed 2:1 supposedly at 601 that are to be opened in another Avid in another city to be output to tape and then ingested into a spot server.  Can they export something native to the spot server?  No.

    They shoot XDCam in HD and edit HD natively, only exporting a SD .mov file at the end.  Not sure if they have Sorenson available to take native HD file and convert to SD.

     

     

  • Tue, Apr 7 2009 10:07 PM In reply to

    • lalittle
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    Re: HD to SD export causes black level shift?

    editz:

    It smells like a 601/RGB mismatch someplace to me.

    This would definitely be my first assumption at this point.  With some programs doing automatic 601 - RGB remapping, it can be difficult to track down where the problem is occurring.

    One thing I've done to troubleshoot this sort of thing is to re-import the movie back into avid (using the 601/709 setting which does not remap the luminance) and look at it in the Color Correction tool.  If the black level is at 32 instead of 16, this will pretty much confirm that an incorrect RGB to 601 remapping is indeed the culprit.

    Another test along the same lines would be to use a test image containing pure white and pure black in Avid and put this through your output chain.  When you import this back into Avid, you'll see elevated blacks AND reduced whites if this is an RGB to 601 remapping issue.  Note that if you use color bars, they may contain blacker-than-black levels (0 instead of 16), so don't let this confuse your conclusions.

    I can't say whether or not QT 7.6 vs 7.5.5 is the issue, but my first guess would be that the problem lies somewhere else.  In my experience since Xpress DV 2 days, QT issues don't manifest in this way.  I'm not saying that this is definitely not the issue -- I'm just saying that my money is on something else.

    Larry

  • Tue, Apr 7 2009 10:44 PM In reply to

    • editz
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    Re: HD to SD export causes black level shift?

    lalittle:
    One thing I've done to troubleshoot this sort of thing is to re-import the movie back into avid (using the 601/709 setting which does not remap the luminance) and look at it in the Color Correction tool.  If the black level is at 32 instead of 16, this will pretty much confirm that an incorrect RGB to 601 remapping is indeed the culprit.

    This is probably the last test to try out.  They've even sent screen caps of all their import/export settings and they look fine both to me and somebody else I've consulted.

    [

     

  • Tue, Apr 14 2009 10:15 AM In reply to

    • lalittle
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    Re: HD to SD export causes black level shift?

    editz,

    Did you ever get this figured out?

    Thanks,

    Larry

  • Tue, Apr 14 2009 1:04 PM In reply to

    • cuervo
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    Re: HD to SD export causes black level shift?

    I hate to tell u this, but, screen caps is the worst possible way to try to diagnose the problem. Screen display is affected by viedeo overlay or video card adjustment and is NEVER a reliable way to guage luma or chroma levels.

    SYS1:ASUS Z97, Haswell 4.0GHz CPU, 32GB RAM, Quadro 4200 + GTX1070, Thunderbolt II -DNxIO-FSI CM171 ///SYS2:ASUS Maximus Extreme V, Sandy Bridge 3.1GHz... [view my complete system specs]

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  • Tue, Apr 14 2009 4:11 PM In reply to

    • editz
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    Re: HD to SD export causes black level shift?

    cuervo:

    Screen display is affected by viedeo overlay or video card adjustment and is NEVER a reliable way to guage luma or chroma levels.

    Are you saying that Avid's own waveform and vectorscope displays are affected by the video card and overlay settings?  When I say "screen cap" that's what I was sending - the scope displays and not the spot itself.

  • Tue, Apr 14 2009 4:13 PM In reply to

    • editz
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    Re: HD to SD export causes black level shift?

    lalittle:

    editz,

    Did you ever get this figured out?

    Thanks,

    Larry

    Nope.  I have yet another FCP user sending stuff they swear is 601 but only imports properly when done as RGB.  I give up.  This market's too small for anyone to truly care about what gets to air anyway.  The stuff I could show you...

  • Tue, Apr 14 2009 4:30 PM In reply to

    • cuervo
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    Re: HD to SD export causes black level shift?

    editz:

    cuervo:

    Screen display is affected by viedeo overlay or video card adjustment and is NEVER a reliable way to guage luma or chroma levels.

    Are you saying that Avid's own waveform and vectorscope displays are affected by the video card and overlay settings?  When I say "screen cap" that's what I was sending - the scope displays and not the spot itself.

    Absolutely NOT! Sorry for the confusion. "Screen cap" means, to me, screen capture. I assumed you meant a screen capture of the image.

    SYS1:ASUS Z97, Haswell 4.0GHz CPU, 32GB RAM, Quadro 4200 + GTX1070, Thunderbolt II -DNxIO-FSI CM171 ///SYS2:ASUS Maximus Extreme V, Sandy Bridge 3.1GHz... [view my complete system specs]

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  • Tue, Jul 13 2010 6:14 PM In reply to

    • editz
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    Re: HD to SD export causes black level shift?

    Here we are, over a year later and we've yet to figure this out. 

    All I can add is that I had the original HD file sent to me in Meridien Compressed, lower field with everything supposedly set to 601.  When I import into a SD project as Resize and 601, the resulting clip is total digital noise/garbage.  When I import it as RGB, the blacks are at 0 and whites at about 90.

    When they do the SD convert on their end, the .mov file imported here at 601 produces blacks at about 7.5 and whites at 100.  Importing as RGB, blacks are about 12 and whites about 90.

    They swear up and down that their scopes show levels at 0 and 100 for both HD and SD versions, so I have no clue what's going on.  I do have effect aperture set at DV25 and NTSC has setup turn on.

     

     

  • Tue, Jul 13 2010 6:36 PM In reply to

    • editz
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    Re: HD to SD export causes black level shift?

    I'm going to attach two images.  "SD" is their coverted file when I import at 601.  "HD" is when I resize the original HD file at RGB.  Remember, when I do it at 601 I get nothing but noise.  No idea what's causing that.

    http://www.ephotobay.com/image/calendar-hd.png

    http://www.ephotobay.com/image/calendar-sd.png

     

     

     

     

     

     

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