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Cleaning s2 is videoclips

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Joined: 03 Feb 2006
Posts: 7
Location: Finland

PostPosted: Fri Feb 03, 2006 11:01 am    Post subject: Cleaning s2 is videoclips Reply with quote

I'll share my experiences on cleaning up low light video clips taken with Powershot s2 IS. The noise in the clips is normally tolerable, but in low light the gain gets very high and so does the noise.

Earlier I have tried to clean my video clips with AviSynth -tools, but failed. The problem is the low frequency noise. Its easy to filter out the high frequency noise, but it does not help, since the low frequency noise alone is more annoying than the original unfiltered noise: it looks like you got some extra movement is the clip jumping randomly around.

A few days ago I made tests with NV and the results were ... promising. The reason for this is the noise in the blue channel. When I separated the RGB-channels, I noticed a big difference in the blue channel noise. While red and green channel noise looks like ... uh ... noise, the blue channel looks like it was made of dust particles. And the particles are quite large, that is, we have got very low frequency noise here.

I have ended up to the following settings in NV:
    - I'm using RGB color space to be able to emphasize the filtering of the blue channel
    - Noise reduction amounts: low freq 100%, other < 50%
    - Noise reduction amounts: blue 100%, other < 50%
    - Very low frequencies on, other options off
    - No sharpening

Still problems to be solved:
    - Frame to frame jumping, but not very annoying. Temporal filtering (4 frames), helps a bit but the rendering speed will be 0.3 fps or less.
    - Slight bluish haze resulting from heavy smoothing of the blue channel
    - Calibration is problematic, NI target squares are too small. In 640x480 clip good calibration (with very low frequencies) requires almost a quarter of the whole frame. Calibration must be made using several frames ...
    - General problem, variable gain in video clips. The noise level can vary a lot during a single clip as the level of light changes.
    - Since the frequency components of the noise at different channels vary a lot, it would be nice to be able to set different spectrums to different color components. Currently the spectrum setting is common to all of them.
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Joined: 01 Sep 2005
Posts: 2237

PostPosted: Fri Feb 03, 2006 12:37 pm    Post subject: Reply with quote

Dear Timo,

Thank you very much for sharing your experience with Neat Video. You seem to understand the tool very well and your comments are very much appreciated.

Regarding the filtration settings used for that type of video clips, you may want to use the default YCrCb working color space instead of RGB. Usually using YCrCb enables more accurate noise reduction. In YCrCb, you would have to intensively filter the Cb channel to reduce those blue low-frequency elements. Very low freq filter should help too, you are right about enable it.

Thank you for summarizing the issues, we will certainly try to find solutions to these issues as we continue developing Neat Video. There may be certain compromises (e.g., analysis area size vs number of frequency components accurately measured and, therefore, number of components accurately filtered) yet we will try to find a way to minimize the drawbacks involved. Indeed, variable gain may require additional adjustments on the part of the filter, we will look into this as well.

Once again, thank you very much!

Kind regards,
Neat Video team
noise reduction for video and photos
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Joined: 15 Feb 2006
Posts: 11
Location: NY

PostPosted: Thu Feb 23, 2006 4:45 am    Post subject: Hi Timo Reply with quote

I too am trying to get rid of low light video noise, and I have
known for some time that its mostly in the blue channel.

I have had some incredible results so far, but either Premiere Pro 1.51
or my matrox RT.X100 card is upset by this filter. FREEZES.

Canopus Procoder 2.0 which usually can handle any transcoding
job in the world cant render a 70 min timeline in 30 hours (normal is Cool
if there is a lot of neat noise reduction.

I am hoping they make it deal with interlaced video since thats what I
shoot and cant change my settings for progressive frames no matter what I do.

Any Ideas.

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Joined: 15 Feb 2006
Posts: 11
Location: NY

PostPosted: Thu Feb 23, 2006 4:47 am    Post subject: normally its 8 hours see above Reply with quote

refers to above
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