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Special treatment for dark regions?

 
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Esp



Joined: 14 Jun 2007
Posts: 5

PostPosted: Thu Jun 14, 2007 12:07 pm    Post subject: Special treatment for dark regions? Reply with quote

Question(s):

There exists a Shadow Smoother filter for VirtualDub. This reduces detail in shadows. Does (or could) NeatVideo include such a process? If not then should I apply the filter before or after NV?

At first I guess it should be applied "after" since it would presumably alter the noise profile (since in my case the only useful noise profiling areas in my frame are in shadows), but then again a cleaner shadow would presumably work better for temporal filtering. A dilemma!

Also are there any other recommended ways of reducing detail more strongly in dark areas than in lighter ones?

Background:

I focus on the problem of dark areas because certain key parts of my footage were shot (by a Sony Z1, subsequently deinterlaced) at extremely low light, which when brightened up (using HRDAGC filter in AviSynth) has resulted in some mostly-horizontal green streaks (like "tendrils of green mist...") slowly drifting across the dark areas. HDRAGC has a "shadows" flag, supposed to enhance shadows, but in my case it had no obvious effect (I guess those tendrils were too bright). This artefact is extremely hard to remove without at the same time geting the plastic/blurry side-effect on people's faces etc.

On the other hand "Shadows Smoother", towards its maximum settings, does at least make some visible degree of reduction in this effect in the dark areas, hence my original question.

I realise I am pushing the boundaries of possibility here, but is there anything that NeatVideo can do or could do (in a future version) about the Z1's "green mist" (assuming my scene doesn't contain real green mist)?

Many thanks,
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NVTeam



Joined: 01 Sep 2005
Posts: 2237

PostPosted: Thu Jun 14, 2007 12:37 pm    Post subject: Reply with quote

Regarding shadow filtration, I think you can do that using NV alone if you adjust the noise profile according to the Filtration of shadow areas idea described in the Neat Image webpage. The same trick can be used in NV to filter only shadows thus eliminating the need for a separate filter.

Regarding the "mostly-horizontal green streaks", if they look like lines rather than random noise then NV may consider them actual details. Of course if you include them in the profiling area then it is less likely to happen, but still it is possible, so I recommend to try building profile using an area with some of these streaks included.

Vlad
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noise reduction for video and photos
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