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Noise artifacts on Alexa's Rec 709 footage


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#1 Demian Barba Toledo

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Posted 04 July 2013 - 10:43 AM

Hi,

 

We just shot a test with the Alexa plus. We shot Apple ProRes 444 on Rec 709. When we saw the test, we noticed that the image was noisy at 800 ISO, OK at 400 and good at 200. Needless to say 1600 ISO was incredibly noisy. Is that always the case or perhaps we has some sort of setting "ON" that created such noise?

 

 

Thanks in advance,

 

Demian Barba


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#2 David Mullen ASC

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Posted 04 July 2013 - 11:04 AM

When people say that they see noise, I have no idea what they are looking at... some people think that any noise at all is bad, that the only good image is noiseless.  Yes, there is some visible noise at 800 ISO on the Alexa and it is cleaner at 400 ISO, but whether the noise you see is normal or a mistake, I have no idea.  Also, what are you judging the image on?

 

Just in case, I'd shoot a test on a second Alexa and compare the two, and also shoot both Log-C and Rec.709 and compare the two, and check it on more than one type of monitor.  Some post houses use plasma monitors which will show the noise more clearly than an LCD or digital projector.  The black levels of the monitor will affect how well you see the noise.

 

I will say that it isn't unusual for commercials shooting in Rec.709 on the Alexa to stick to 400 ISO to get a clean image.

 

At 200 ISO, you run the risk of clippy highlights that make the image feel video-ish.


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#3 Demian Barba Toledo

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Posted 04 July 2013 - 11:31 AM

Thanks David. I know "noisy" is a subjective statement, I guess I was expecting a cleaner image from the Alexa at 800 ISO. I also have to admit it was shortsighted from my side not to do a comparative test between Log C and Rec 709. Tomorrow morning I will run the same test on the same camera, this time on Log C. Testing another camera might not be an option since our rental house has only one body. Today at the post house I brought up the possibility that the monitor was causing the noise, but the colorist rejected that idea. I will insist tomorrow on see the test on more than one monitor.

 

Thanks again,

 

Demian


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#4 David Mullen ASC

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Posted 04 July 2013 - 11:43 AM

I color-corrected "Smash" on a DLP cinema projector, but when I got back to L.A., I had to see it on a CRT and plasma monitor, and between the three, the plasma showed a lot more noise.


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