Hi Tom, On Wed, 01 Jan 2003 09:56:09 -0500, Tom Reese wrote:
> Anyway, could you elaborate on your comment about scanning > artifacts? What are they? How do you deal with them? First off, there's the unavoidable softening of the scanned image compared to the original piece of film. Secondly, there's the "speckles" and "fringes". They generally get called grain aliasing (GA). GA is caused by the way that scanned pixels line up with the color-producing grains (or dye clouds) in the film. A scanned pixel could "see" the edge of one or more grains, producing some intermediate color that can be different from the one your visual system would produce for that spot on the film. It can also happen that adjacent scanned pixels "see" two different grains of different colors. Each could produce a nearly pure rendition of the color of that grain, even though it was only one component of the color at that spot on the film. The scanned pixel just didn't "see" the other grains in the other color layers that made up the color at that spot on the film because they weren't lined up vertically. GA can appear in any part of the scanned image. There's also scanner system noise. This has causes ranging from dust in the scanner's optical path to the signal-to-noise ratio of the optical sensor in the scanner. It typically appears as speckles in the parts of the scan that are very dense on film. So, dark areas on slides and light areas on negatives. There are probably other causes I'm ignoring, too. Basically, most scanned film images seem to want at least a little shot of sharpening. To combat the speckles, you can drop to 2000 dpi. This changes the relationship of the size of the film grains (dye clouds) and the size of the scanned pixels and eliminates almost all of the speckles, though fringing can still occur. Searching Google for grain aliasing and/or Nyquist should bring up some gory details, if you want to go that far. If you really need 4000 dpi for the size of print you want to make, then look into the software at http://www.neatimage.com/. If an image has a large enough featureless rectangular area, you can use their software to "subtract" the average noise, smoothing the image. You can also use your photo editing software (Photoshop, etc.) to add a little Gaussian blur to the image. That will knock the "edge" off the speckles and fringes, so sharpening won't make them stand out in the final image. TTYL, DougF KG4LMZ
