Noise removal questions

[jammer_jammer]

<p>I have scanned about 2 thousand Kodachromes with the Nikon V ED. Unfortunately I found out that Kodachromes are not the easiest slides to scan, particularly if they are underexposed. Of course, back in the day when I was using Kodachrome, I would very frequently underexpose on purpose for color saturation. So, I ended up needing to crank up the exposure during the scanning process. All that to say that I have a whole crap load of scans with unexceptable amounts of noise/grain or whatever it may be.<br>

I've never experiemented with noise removal and plan on trying out the demo of Noise Ninja very soon. I do very little printing so I'm asking these questions to those of you that have a whole lot of experience in that area.<br>

1. At what percent magnification should I look at the image in Photoshop while making my noise removal decisions?<br>

2. Is it OK to go ahead with noise removal on all of the full size TIF files or should I only do noise removal on files AFTER they have been resized for output?<br>

3. I've read that a good bit of noise that one may see on the screen does not really show in print and therefore you don't need to remove quite as much noise as you would think. Do you find this to be true?<br>

4. I don't really care about slight noise and I bet that the majority of regular folks don't even notice it so I'm thinking that I would like to remove noise selectively only where it is very obvious and try to leave details alone if possible. Is this cool or would it be real obvious in print where the part that has noise removal with look very obviously different than the part that doesn't?<br>

Thanks to anyone who has a lot of experience in noise removal and printing who helps me with these questions.</p>

[sattler123]

<p>I use NoiseNinja. The issue with under exposed slides is very dificult and there is only so much NoiseNinja will be able to do. There is always a balance between removing noise and softening the image. The easiest slides to scan are those that are slightly over-exposed (by 1/3 stop or so).<br>

Anyway - when you use NoiseNinja, it will switch to a 100% crop of your picture automatially and you will be able to see the effect immediately. NN has tons of controls and it takes some time to figure them all out - just use the auto settings in the beginning to get a feel for NN.<br>

You should apply NN before you size any of your picutres - in fact NN recommends that Noise removal should be one of the first steps after importing your picture.<br>

Yes, noise on screen is more visible than in prints - it very much depends how big you print of course. BTW when you down size a scanned file much of the noise will actually disappear.<br>

Good luck with your project - let us know how you made out.</p>

[robert lee]

<blockquote>

<p>I've never experiemented with noise removal and plan on trying out the demo of Noise Ninja very soon.</p>

</blockquote>

<p>I use Neat Image and find it a better implemented noise removal package. Trials are free. Just download it.</p>

<p>Actually, enable multi-scanning before you use any noise removal program at all. This provides a cleaner source image at the start. Each scan doubling is equivalent to gaining one extra tonality bit (or think of it as having a less and less noisy scanner CCD imager.)</p>

<blockquote>

<p>1. At what percent magnification should I look at the image in Photoshop while making my noise removal decisions?<br /> 2. Is it OK to go ahead with noise removal on all of the full size TIF files or should I only do noise removal on files AFTER they have been resized for output?</p>

</blockquote>

<p>This really has to do with the intended output size. The noise components of an image tend also to be at the highest spatial frequencies. Noise removal is really just judiciously done low pass (and band pass) filtering. This is why when printing to modest dimensions, say 4x6 output even from the noisiest 4000dpi Nikon scan will essentially show no noise. The down sampling for print is effectively a global low pass.</p>

<p>Having said this, apply the noise filtering at the very front - to the 16bit 4000dpi TIFF from the scanner. This gives the highest quality file for large prints (which will only output even better looking prints at smaller enlargements.)</p>

<p>By the way, use a frequency domain sharpener like Focus Magic after the noise has been knocked down with Neat Image. With the bulk of the noise already removed, only the image components are emphasized and sharpened.</p>

<p>The resulting file is the digital negative on which to start further digital darkroom work.</p>

<blockquote>

<p><br /> 3. I've read that a good bit of noise that one may see on the screen does not really show in print and therefore you don't need to remove quite as much noise as you would think. Do you find this to be true?</p>

</blockquote>

<p>Depends on the format size, the print size and the film. Even at 8x10, noise from 135 format 160ISO portrait film is aparent on the print when compared to a noise reduced image side by side.</p>

<p> </p>

[jammer_jammer]

<p>Thanks Robert.</p>

[don_e]

<p>Is it color noise in the shadows due to the underexposure? When I have it in a scan I find that Lightroom's chroma noise filter set between '10-30' removes it -- but I am not scanning Kodachrome. If it works for your scans, you could sync the noise filter to all 2 thousand and be done with it while you have a snack.</p>

<p> </p>

[jammer_jammer]

<p>Thanks Don. I don't have LR but I could experiment with some other chroma filters.</p>