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
- - 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.