Noisy Blue Channel

[JR Monteiro]

I just did a green screen shoot and noticed some blotchy noise in the picture in the skin tones and even in the background. I thought it might be my monitor but when I brought it back to the office and looked at a few frame grabs in Photoshop here is what I saw. Is this normal or do I have a problem with my camera? I was shooting with tungsten light as opposed to daylight balanced bulbs but would it make that much of a difference? The stills are marked as to what ISO and exposure settings I was using. The most prominent noise was seen on the woman shot at 640ISO and underexposed by one stop which would stand to reason if it were low light noise. But the noise indicator bar on my Red LCD monitor was clean. There are two frame grabs for each shot an RGB and a Blue Channel only. The Red and Green channels were clean. I remember seeing this on my old Red One prior to the MX chip. Is this the best I can expect from my new Epic under these lighting conditions or should I be contacting the service department?


http://www.redsolutions.tv/Red/1a.jpg
http://www.redsolutions.tv/Red/1b.jpg
http://www.redsolutions.tv/Red/2a.jpg
http://www.redsolutions.tv/Red/2b.jpg
http://www.redsolutions.tv/Red/3a.jpg
http://www.redsolutions.tv/Red/3b.jpg

[Gunleik Groven]

Hard to tell much from this post...

Links are still bad...

What would be of more practical help, would be a single r3d snapshot from each exposure...

[Gunleik Groven]

Well, this is about as I would expect it with the meta whiteballancing.

Is it causing you problems?

In that case, I'd maybe have tried to set the WB not lower than 4400 kelvin, and do the rest in a grading app.

But it's hard to really say anything meaningfull about this without having some r3d's to look into...

[Brook Willard]

JR,

Please post an R3D still file so that we can see the "original negative".

[JR Monteiro]

I repaired the links and they seem to work now. These are R3D Snapshots converted to jpegs

[Gunleik Groven]

We need the R3d snapshots to say anything meaningfull about this. Jpg's aren't much for analysis...

[JR Monteiro]

Thanks for your help here are the original R3D files I could only get two links to work

George


http://www.redsolutions.tv/Red/A002_...1.0000312F.R3D
http://www.redsolutions.tv/Red/A002_...1.0000034F.R3D

[Gunleik Groven]

'couple of issues here.

3k, means less scaling of the noise. Strange choice for a keying shot.

Attached is a screendump of the waveform/histogram of the shot of the woman at 3g3/RC3/320/5000 which is closer to sensor native.

As you can see, there is very little exposure in the blue channel, and thus it has to be gained, and that generates noise.

Not really a noisy channel issue as much a noisy exposure issue...

[Thomas Koch]

Looking at the R3d, when you reset everything to default, it looks good, except the white balance. I typically rate the camera at ISO 320 when shooting Tungsten, so going even more yellow with the lights i'd rate it lower to reduce noise. Otherwise, use daylight balanced light at ISO800. That all produces good noise levels. What's happening here, is that you are not providing the sensor with enough blue light.

That's just my opinion. I'm sure others will have more definite answers.

[JR Monteiro]

That is what I was thinking because the footage rated at lower ISO looked cleaner. I just wasn't sure about the exposure limits of the Epic. I won't make that mistake again. Thanks.