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Digi tape gamma shift

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Thomas Moriarty
Digi tape gamma shift
on Feb 13, 2012 at 3:23:43 am

Hey all,

Our current pipepline at the moment is:
1. to export master files to .mov format (rgb uncompressed 10 bit)
2. import into final cut (pro 7), then master to Digi tape from there.
We're using blackmagic uncompressed 10 bit to put to tape.

The problem is that whatever goes on the tape is washed out compared to the master file. There is a definite colour shift.

We did find a work around that works, which is to re-export the file from Nuke in uncompressed 10-bit with gamma 1.8 colourspace. The only problem is that this is time consuming.
I was wondering if anyone might have an idea as to what's causing the colour shift, and how we might be able to deal with it directly in Final Cut?


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Bret Williams
Re: Digi tape gamma shift
on Feb 13, 2012 at 4:17:32 am

Are you monitoring the tape differently than the output of the blackmagic? Could be a black level issue. If you're playing the digibeta out to a monitor via composite or svideo, it should be adding setup, which would look extremely washed out if you had the monitor setup for 0 black level.


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Michael Gissing
Re: Digi tape gamma shift
on Feb 13, 2012 at 4:41:03 am

I think the Blackmagic codecs are YUV not RGB. Perhaps you need to stay within the one codec. Can you load the Blackmagic codec on the source machine. Gamma of 1.8 is wrong so it sounds like a fix of mistake. Better to sort the mistake.

Ditto Brets comments about the setup for black levels and how are you monitoring everything?


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Thomas Moriarty
Re: Digi tape gamma shift
on Feb 13, 2012 at 5:11:00 am

The source files are being output from Flame in RGB uncompressed 10 bit. The test that we ran is as follows: First we put the footage to tape straight from flame. Then we put the same footage on the tape from FCP. This is where we saw the differences. Both were viewed on the same monitor.
I suspect that the colour change is coming from the conversion of the RGB master to YUV in final cut, and also the use of the blackmagic codec to put to tape.
On a side note, it's not often that I would have access to the Flame machine, hence why I need a Final cut pro workflow (for tape mastering).


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Michael Gissing
Re: Digi tape gamma shift
on Feb 13, 2012 at 6:07:36 am

AJA have a 10 bit RGB codec from memory. Perhaps Blackmagic also do. Blackmagic also has software to output a file directly so maybe you don't need FCP at all unless you are adding something to the Flame output.


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Jeremy Garchow
Re: Digi tape gamma shift
on Feb 13, 2012 at 6:22:53 am

If FCP is reading the file as RGB, you should be able to change the gamma in FCP.

Right click > Clip Properties > Format.

Look for the gamma field.

Can you change it? If so, FCP is reading the file as RGB.


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Jeremy Garchow
Re: Digi tape gamma shift
on Feb 13, 2012 at 4:55:18 pm

Sorry, I misspoke last night.

It's right click on clip > Item Properties > Format.

Then look for "gamma level".

If a clip is in the timeline and you change it in the browser, the clip will not update so you will need to change every instance in the timeline, or change it in the browser and reedit the clips back in to the timeline.

With a codec like 10b UC, it might not give you the options as FCP probably isn't expecting that codec to be RGB as the codec is probably YCbCr. The codec needs to be a true RGB codec (Animation is an example) for the gamma level to become selectable.

Jeremy


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