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Variable gain - variable noise

 
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Timo



Joined: 03 Feb 2006
Posts: 7
Location: Finland

PostPosted: Sun Feb 05, 2006 9:39 pm    Post subject: Variable gain - variable noise Reply with quote

Video cameras contain an automatic gain control. In low-light conditions the gain becomes very high, and the noise usually becomes visible. NV is capable of removing, or at least reducing the noise considerably. This is possible if the calibration is made using the same gain as the processed clip.

But how NV handles the case where the lightning conditions vary a lot during the video clip? Is the Noise level setting useful in Noise filter settings? I studied this by recording a video clip that started from my room's corner and ended to a clear blue sky seen through the window. I also made a single video frame that contained calibration targets recorded at variable lightning (=gain) conditions.

My goal here is to find settings for NV that:
    - leave the frames that are taken in good lightning (low gain) untouched
    - reduce considerable the noise in frames taken in low light (high gain)

First I built the Device noise profile using calibrations recorded inside, that is, when the noise is the highest. I applied the profile to a frame that contained items recorded with varying gain settings. Some parts of the frame contained more noise and some less noise. Next I studied how the Noise level setting works in practice. The text in the manual was not very promising since it said that low elements are filterd out and high elements are preserved. And the Noise level sets where the limit between low and high is. My tests prooved that the setting did exactly what the manual said. I could not find a setting where the low noise test target would be preserved and the high noise would be filterd out. I instead did find settings where the low noise is filterd out and the high noise is filtered only partly.

Next I left the Noise level settings in their default positions and processed my video clip. The result was satisfactory. Some details were lost in the low-gain part, and the noise in the high-gain part was reduced a lot, but is still a bit annoying.

The Noise level setting is probably useful in processing photographs where the noise levels are quite low. But the situation is quite different when we talk about videos taken with digicams and home camcorders. I wonder if the inverted Noise level setting could help in filtering home videos. That is, the noise below a certain level is preserved, and only the higher elements are reduced.
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Joran



Joined: 08 Jan 2006
Posts: 47
Location: Oslo, Norway

PostPosted: Thu Feb 09, 2006 2:02 am    Post subject: Reply with quote

Hello

I think your contribution is very interesting reading. Continue testing and please chare your experiences with us!

Best wishes,
Joran
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kbot



Joined: 15 May 2007
Posts: 1

PostPosted: Tue May 15, 2007 8:31 am    Post subject: Reply with quote

What could Neat Video team advise to process such variable-gain videos?
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NVTeam



Joined: 01 Sep 2005
Posts: 2237

PostPosted: Tue May 15, 2007 9:33 am    Post subject: Reply with quote

We recommend to use Adaptive Filtration option in the filter settings to automatically adjust filtration to the changing noise.

Vlad
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Neat Video team
noise reduction for video and photos
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