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[filmscanners] Re: Channel alignment test for B&W scanned as RGB

Are you sure this isn't a result of the different focal points of
different colors?

You've probably noted that infrared, for instance, has a fairly large
difference in focal point than the visible spectrum (the offset is
indicated on most lenses as a red line or dot).  This holds true for the
visible spectrum as well, but it is not usually that noticeable until
you  look pretty closely.

However, it is true that the film could shift, wobble or change
dimensionally enough that the difference at scanning times/location
could show up as well, since the tri-line sensor is actually recording a
different part of the film for each color at any one point in time.

 >>>=================================>>>> film
            \|/    \|/    \|/
              CCD    SENSOR


Simon Lamb wrote:

> There is a debate on-going on the Imacon users list regarding channel
> misalignment when scanning black and white stock as RGB.  If anyone has the
> time to undertake a smal test could you do the following:
> 1. Scan a black and white negative as Positive and save at max resolution as
> 16-bit RGB.
> 2.  Open the file in Photoshop and view at 100%.  Using the channels
> palette, skip between the R, G & B channels (Control 1, 2 & 3) and look to
> see if the image moves (sometimes by between 2 and 4 pixels) between each
> channel.
> 3.  If it moves then it shows other scanners have the same problem aligning
> channels when scanning monochrome stock using RGB sensors, which in some
> cases causes the image to show stretching across the grain.
> Useful scanners to try this on would be those competing in the Imacon Photo
> arena (Nikon 8000, Sprintscan 120, Multi Pro etc.).
> Thanks to anyone who can do this test and post their findings.
> Simon

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