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Color Issue - White Matte Block Appears Gray on TV

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Antonis Andrea
Color Issue - White Matte Block Appears Gray on TV
on Jan 24, 2012 at 2:34:55 pm

I shoot with an infinite white background and in editing often block out lights, equipment and other gear in the periphery of the shot with matte white blocks color matched to the white screen in the shot.

It always appears seamless on preview and when exported and played on most screens. But occasionally these blocks will appear gray instead of white on tv screens.

What is happening and how do I avoid this?? It is a pain.


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Neil Patience
Re: Color Issue - White Matte Block Appears Gray on TV
on Jan 24, 2012 at 4:22:56 pm

My first thought is that are your whites set to peak white at 1V or are they over ?

My reason for asking is that if they are over although your patches appear to be invisible they are in fact at slightly lower level but disguised by everything being a bit over.

When played on a TV the TV is limiting the white by bringing the level down. As this is an overall gain reduction this in turn exposes your patches as slightly grey.

Where the levels are not so over no limiting happens and the patches blend in.

Anyway as I said just a thought.

best wishes
Neil
http://www.patience.tv


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Antonis Andrea
Re: Color Issue - White Matte Block Appears Gray on TV
on Jan 24, 2012 at 4:44:40 pm

Very helpful! Thank you. Yes, that would make sense. How do you limit the peak? I am, essentially, cranking up the whites on the video image (color corrector) until my background is to my liking and then making matte blocks and selecting the background as their color. Yes, the person in the video is often overexposed in post because of my need to crank so much up.

I know I should start with background that is brightly lit, avoiding much need to do that in post. But I do try to remove that yellow of the background by turning up the whites.

So, by doing that I'm maxing out the capabilities of what some screens can tolerate?

Could you advise a good process/workflow and how I would avoid the issue?

Thanks so much!
Tony


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Neil Patience
Re: Color Issue - White Matte Block Appears Gray on TV
on Jan 24, 2012 at 5:35:17 pm

From your description it certainly sounds like you are overdoing the whites especially since its making your subject overexposed.

I would suggest first you read up on using the video scopes as this will give you a much better understanding. I would suggest the waveform monitor and the parade are a good start. But essentially an understanding of the video waveform and its spec is going to help you loads.

Then have a read up on the 3 way Colour Corrector.

Those 2 things are the answer to all of your exposure/white balance issues.

However very basically:

Go to the tools menu and select video scope.

Use the waveform monitor to measure your image. You will clearly see white and black marked.

Use the 3 way colour corrector to make your whites peak white, and to get a balance between that and your subject.
Also use this to correct any white balance issues (your yellow cast) rather than just blowing it out to "fix it"

It may be that you need to go over to get an even white but dont just ramp it right up.
Then you can patch as before.
You can then use the broadcast legal filter to clip any peaks.
But again dont use it as a catch all take care to balance your whites as much as you can first.
This will ensure that everything is at peak white and no more.

You should then find that the limiting/clamping issues that you are seeing go away as everything should then be in spec.

best wishes
Neil
http://www.patience.tv


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Antonis Andrea
Re: Color Issue - White Matte Block Appears Gray on TV
on Jan 24, 2012 at 6:25:58 pm

Extremely helpful, thank you!


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Dave LaRonde
Re: Color Issue - White Matte Block Appears Gray on TV
on Jan 24, 2012 at 5:56:36 pm

[Antonis Andrea] "Could you advise a good process/workflow and how I would avoid the issue?"

Motion. You can match both the video and the background, mask the parts that need masking, feather the masks as necessary to make them seamless and render a completed quicktime movie of the shot in your editing codec.

Dave LaRonde
Sr. Promotion Producer
KCRG-TV (ABC) Cedar Rapids, IA


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Antonis Andrea
Re: Color Issue - White Matte Block Appears Gray on TV
on Jan 24, 2012 at 6:26:31 pm

Great advice. Thanks very much.


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