Defeating The Dreaded Fixed Noise Pattern

While that's a good-looking shot at 800 ISO, and I agree that the key to avoiding the fixed-pattern noise is lighting, it is not always so simple.
Here's a problem I encountered on my short film shot on the GH1. What happens if your shot is SUPPOSED to look a bit underexposed? For instance, what if your actor's face is not the brightest part of the frame? Even if you are using good lighting and the shot is well-exposed, the actor's skin in this shot is prone to fixed-pattern noise because the luminance value of the skin falls on a range the GH1 doesn't reproduce well.
So you have to resort to some tricks to solve this problem. My solution is to overexpose by 1/3 to 2/3 of a stop, or add a bit more fill light than you otherwise would on the face. Then you have to bring it back down in post to the level you want. That seems to eradicate the fixed-pattern noise, as well as crushing regular noise into the blacks, too.
 
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Man, you know what? I've been looking at some of my recent posts, and realize that they can come off confrontational and/or patronizing. I REALLY need to concentrate on how I phrase things, as that is not my intention. So anyway, the above post was not meant to diminish your thread. I only wanted to add additional info that I had encountered a scenario that needed a little more thought and TLC with the GH1's exposure. Have a good day! :-)
 
October Black said:
I was at iso 800 in that shot.
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?. I don't get it. are you saying it's fine to shoot @800iso as long as you light properly and you'll avoid fix pattern noise?
you can have fpn in broad daylight if you have a slow lens and high iso.
to me there was very little solution there other than to drive traffic to your website. but i'm not opposing that, just that
stating lighting is going to get rid of fpn doesn't add up.
 
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dvbrother said:
Here's a problem I encountered on my short film shot on the GH1. What happens if your shot is SUPPOSED to look a bit underexposed?
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My approach has always been to light the talent. If I need to bring the level down, I'll do it in post. The trick is making sure your contrast ratios are right during the shoot.
 
Car3o said:
?. I don't get it. are you saying it's fine to shoot @800iso as long as you light properly and you'll avoid fix pattern noise?
you can have fpn in broad daylight if you have a slow lens and high iso.
to me there was very little solution there other than to drive traffic to your website. but i'm not opposing that, just that
stating lighting is going to get rid of fpn doesn't add up.
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Its dark right now, so I can't comment on stopping the lens down outside during the day. But, I just did a test using ISO800 at F22 with a bare 60w light bulb, no FPN.

Tomorrow I'm going to test outside and see what happens.
 
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October Black said:
My approach has always been to light the talent. If I need to bring the level down, I'll do it in post. The trick is making sure your contrast ratios are right during the shoot.
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That's exactly the point I was making...not very well I guess. But the thing that makes it tricky is this: what's traditionally considered good lighting for film, and even other video cameras doesn't always apply to the GH1 because there's a luminance range where FPN shows up. So you have to have a LOWER contrast ratio than you might think. That means adding more fill light to shadow areas, then darkening them in post. It has nothing really to do with "lighting the talent" since the shots I'm talking about that exhibited FPN were well-lit by normal standards. But the FPN showed up at 320 ISO. If I had exposed 1 stop hotter, then brought it down in post, it would have been fine. Or brightened the fill light a bit and added contrast later. That's what I meant in my previous post.
 
If I light the actors FPN is no longer an issue...period.

I have two GH1s and both work this way. Look at this screen grab. It's pretty clean and it has a high contrast ratio.

1264569696.jpg
 
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because you exposed for the actor, why would you have fpn? fpn only shows up if you expose for darker areas and push it higher than it's capable. say you tried to expose for that cabinet in the back without pushing any light on it. fpn would be all over the place.
 
This is good to know. You should do some tests at 1600 iso. I've shot stuff at 1600 iso and I like the look. Not FPN, but a certain different grittyness.
 
October Black said:
I think you misunderstood what I was trying to say regarding contrast ratio.
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No, I didn't misunderstand. I think we're answering the same question from two differing approaches. I wish I had a frame grab from my film to show, but I don't. I lit two actresses with contrast ratios that were appropriate and looked good. It was lighting that would have looked good had I shot film or on say an HVX200. But I learned the hard way that you have to treat the GH1 differently in lighting like this. Because the skin tones of both actresses both had FPN. I learned that I should have exposed 2/3 to 1 stop hotter, then brought things down in post for a proper look.

The image you posted above is contrasty and takes place at night but your actress's skin is still above the threshold where FPN manifests (and rightfully so...you did a fine job of lighting.) But imagine an "X-Files"-ish scene where you barely want the actor's face to be visible. A scene where the face is not the brightest element of the scene...just a little light in their eyes. It's not just a matter of contrast ratio. I know I'm beating a dead horse here, but I'm saying you must expose a scene like that much hotter than you think, then bring it down in post. And what I mean by a LOWER contrast ratio in that situation is this: since my hypothetical scene has a brighter element (say a light source like a lamp) in it, if you expose hotter, you risk overexposing the lamp. So you have to add fill light or in some way decrease your contrast ratio to avoid clipping. Again my whole point is you need to be more cognizant of things like this with the GH1 as opposed to say an HVX200.
 
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Here's a trailer for the film I'm talking about. The shots I'm referring to are the early shots of the girl with dark hair and, later, the 2-shot of the girls sitting at a table with the candle between them. You can't see the FPN because it's been downrezzed for Vimeo. I can't get the video to embed on this page so you'll have to follow the link

http://www.vimeo.com/7449911
 
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I've found that both After Effects 'Remove Grain' plug-in and Neat Video deal quite well with reducing the FPN, especially when the take has camera movement.
 
October Black said:
Tomorrow I'm going to test outside and see what happens.
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Yesterday I went outside to try and push the GH1 to it's limits at ISO 800.

No FPN until I hit f22 with the shutter speed set to 640. At this point the histogram was underexposed, so FPN wasn't a surprise.

I think the biggest factor when dealing with FPN is keeping your histogram full .

It works for me.
 
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