How to deal with Scanner Shadow Noise

[david_williams11]

Hello,

 

I have a Nikon Coolscan V and I am wondering how to deal with shadow

noise caused by the scanner CCD. To me, it seems this noise is at

its worst when I scan an image at the full 4000 dpi resolution.

This noise doesn't show up as noise when I make a print, however it

does have the effect of increasing the contrast between dark shadow

area and a light area. Sometimes, this makes the transistion from

dark to light look unnatural and clipped. I'm not exactly sure how

to deal with this. Noise Ninja demo seems to remove this CCD noise

at the expense of sharpness but it does smooth out the

transistions. Scannning at a lower resolution helps but I don't

always want to do that. Are there any other scanner parameters I

should change or anything else I should do? I'm just using Nikon

Scan right now.

 

I've attached a section of an image to illustrate the noise. The

image has been lightened dramatically to show how the noise only

appears in darker areas.

 

Thanks<div></div>

[awindsor]

Is this a negative or positive scan ? I have had success blending two distinct scans. Using CanoScan FS4000 and VueScan I have found that the autoexposure is uses short exposure time to minimize purple bloom and highlight clipping. Tripling exposure time results in blown out highlights but more shadow detail. VueScan has an automatic long exposure pass option which can help with shadow detail.

[Ed_Ingold]

Your example does not look like detector noise. It does look like a combination of other effects. I believe this sample to be from a transparency, though you do not say.

 

Look at the histogram in Photoshop (or NikonScan preview). It looks like the dark range is being clipped. If so, adjust the exposure. If necessary, adjust the curves to prevent clipping on the high side as a result. In chromes, the scanner Dmax may be exceeded. If so, adjusting the "analog gain," which actually lengthens the exposure time, may help.

 

Secondly, Digital ICE and GEM sometimes create patterns of this sort in high-resolution scans. It is visible in areas with little contrast, generally like blue sky.

 

Finally, look at the original image under 25x magnification or so. The original is probably a transparency, which sometimes show grain artifacts in shadow areas. The Nikon, at 4000 ppi, cannot truely resolve grain in chromes, but enough at high resolution to form alias patterns, which resemble your example. With negatives, you see this effect in highlights, which is much more troublesome.

[Ed_Ingold]

You may also try using multiple scans, if your scanner allows. This will smooth out semi-random patterns in dark areas, at the expense of sharpness elsewhere and greatly increased scan times. 4x is a good place to start. This won't help the blocky transition between light and shadow, which is caused by other problems.

 

From a philosophical point of view, you should take a step back and decide if this is a killer issue - is it really visible in prints. Sometimes we keep looking until we find a problem, then fret needlessly. If you actually have a 25x loupe (I do), I extend my sympathy.

[david_williams11]

The scan comes from a Velvia slide