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Excessive grain under low light


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#1 J Costantini

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Posted 02 June 2005 - 07:21 AM

Hi.
I have a dvx100 which has been used moderately for 2 years now. It has about 300 hours of use, including capturing sessions.

on my last experiences I have noticed excessive grain (or video noise) when I shoot under low light conditions or even when I have a well lit frame but a small part of it is in the dark it shows a lot of grain there.

I normally shoot at the maximum aperture.

Do you think it may be the age or is it a normal characteristic? I can't really remember if it used to be that grainy before... i don't think so. It doesnt matter if i'm using the 24P mode or not.
Have you experienced excessive grain with this camera ? have any idea of what could it be?
Please post.

Thanks
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#2 Nate Downes

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Posted 02 June 2005 - 10:46 AM

That's normal for any video camera, even the high-end HD cams. It's cuased by a lack of information hitting the sensor, you see the electrical noise in the system.
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#3 David Mullen ASC

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Posted 02 June 2005 - 11:20 AM

Is your gain set manually to "0" or is it on auto-gain?

If so, the problem could just be that the gamma setting you are using is designed to create a lower-contrast image in the shadows. There's no free lunch here; often gammas that give the video signal a flatter "film look" also add noise. Crushing the blacks a little -- maybe adding a little more fill to compensate -- will help hide noise better.
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#4 J Costantini

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Posted 02 June 2005 - 08:28 PM

Is your gain set manually to "0" or is it on auto-gain?

If so, the problem could just be that the gamma setting you are using is designed to create a lower-contrast image in the shadows.  There's no free lunch here; often gammas that give the video signal a flatter "film look" also add noise.  Crushing the blacks a little -- maybe adding a little more fill to compensate -- will help hide noise better.

<{POST_SNAPBACK}>



Thanks
It's just that it seems to be impossible to have both GOOD CONTRAST and LITTLE GRAIN on the same video image... no matter the camera you're using... the F900s, VARICAMs and VIPERs must get closer... i dont know
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#5 David Mullen ASC

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Posted 02 June 2005 - 11:11 PM

Thanks
It's just that it seems to be impossible to have both GOOD CONTRAST and LITTLE GRAIN on the same video image... no matter the camera you're using... the F900s, VARICAMs and VIPERs must get closer... i dont know

<{POST_SNAPBACK}>


Depends on how you define "good contrast" -- if by good, you mean low, then most ways of lowering contrast in video can bring up the noise level.

On the other hand, low contrast images in film tend to bring out the grain level, so it's not like film is immune from the problem either.

In both cases, either using more contrast in the lighting or using a slow-speed stock (or shooting at minus-gain in video) will help reduce visible grain / noise.

Yes, HD tends to have less visible noise than SD, but if you project it on a 75' wide theatrical screen, the noise can become visible again.
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#6 J Costantini

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Posted 02 June 2005 - 11:32 PM

Depends on how you define "good contrast" -- if by good, you mean low, then most ways of lowering contrast in video can bring up the noise level.

On the other hand, low contrast images in film tend to bring out the grain level, so it's not like film is immune from the problem either.

In both cases, either using more contrast in the lighting or using a slow-speed stock (or shooting at minus-gain in video) will help reduce visible grain / noise.

Yes, HD tends to have less visible noise than SD, but if you project it on a 75' wide theatrical screen, the noise can become visible again.

<{POST_SNAPBACK}>


For good contrast I meant "high contrast". It is hard for me to obtain very constrasty images using video, specially DV, because if I leave parts of the frame unlit or underexposed it will show grain, which sometimes is not wanted. Is that a fact for all of us or my camera may be bad or not properly set?

Edited by nillo, 02 June 2005 - 11:36 PM.

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#7 David Mullen ASC

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Posted 02 June 2005 - 11:41 PM

For good contrast I meant "high contrast". It is hard for me to obtain very constrasty images using video, specially DV, because if I leave parts of the frame unlit or underexposed it will show grain, which sometimes is not wanted. Is that a fact for all of us or my camera may be bad or not properly set?

<{POST_SNAPBACK}>


At 0 db, you shouldn't get noise in high-contrast images unless your camera is set-up incorrectly, or it is screwed up, or has bad menu set-ups, or is slipping into automatic gain boosting.

Basically it sounds like your Master Black video level is not low enough and/or you possibly have some sort of Black Gamma or Stretch engaged to lower contrast in the shadows, or you have the gain on auto so when you hit wide-open on the iris, the gain is kicking in to compensate.

I mean, if you set the gain to 0db and put the lens cap on, does the all-black frame look noisy?

What Gamma setting are you using? Cine, Low, High, or Normal? Since Cine-Gamma has a rather flat but straight response to light but a lifted bottom end, you are supposed to underexpose overall a little... but to reduce noise, you'd really have to compensate by lowering the Master Black video level. If you want more contrast, try switching to another Gamma setting like Normal or High.
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#8 Brian Wells

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Posted 05 June 2005 - 11:30 AM

I think crushed blacks on DV tend to pick up compression and blocky pixels on occasion.. maybe that's viewed as "grain" in some contexts. In Final Cut Pro, I have a "Black Restore" filter which helps reduce the visual effect of noise/grain in the blacks.

However, I feel that more likely what you're seeing is the by-default low contrast look the DVX has out of the box, which can be adjusted for a higher contrast look using the "Master Pedestal"

I like this visual explanation of "Master Pedestal" provided by Jarred Land, specifically for the DVX.
http://www.dvxuser.com/articles/MP/


Hope this helps,

Brian
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