Is this right? If so, I have misunderstood the operation of ICE (which I
don't use, but I'm endlessly curious!)
I thought that ICE used infrared simply to image the dust and other
physical imperfections, and that the normal photographic image is
relatively transparent to IR. Then (I assumed) it lined up the defects
with those on the non-IR scan, and used some sort of 'intelligent
interpolation' to remove the defect. If that is how it is done, you would
expect some softening at the defect, but there need not be softening
elsewhere.
Perhaps I am misreading the explanation below, but it sounds like you're
saying the scanner uses the IR channel in a way that would cause either a
focus or registration problem. Surely when the scanner uses IR it *must*
either refocus or move a set distance to compensate for the different
focus (which should include the distance from the image plane to the dust
plane). So the final images it uses for the processing should all be in
focus, whether they were of the dust, or of the image..
Sorry if I'm missing something or if this has been covered in endless
detail previously!
Mark T.
At 08:14 PM 19/02/01 -0800, Arthur wrote:
..
>In spite of what our friend from the developers of ICE,
>their magic does soften the results, and this is with good reason. If
>you have even noticed, there is a little red line on most lens barrels,
>which is off center from the focus line. The reason for this line is to
>show the differences in focus point between visible white light and
>infra red, for people who are using infrared films. One makes the
>focusing using the white light image in the viewfinder, and then moves
>the lens barrel the amount of the offset this red line provides. The
>image now looks out of focus in the viewfinder, but is in focus for
>infrared, which has a different wavelength than white light.
>
>Actually, to go one step further, the focal point from red, green and
>blue light are all different. If you had a very precision, very narrow
>depth-of-field optics and you were to photograph an image through three
>different filters, (red, green and blue) you would find each focuses at
>a slightly different point. This might even explain why the three color
>separations made in CCD scanners are not always equally sharp.
>
>Since, as I understand it, d.ICE uses the infrared image as one
>component in the final image (even if it is subtractive in nature) the
>fact that it is likely out of focus probably causes a softening of the
>whole image, however slight. This is not to "slight" the genius behind
>the process, but unless there is some way to refocus the infrared
>channel, (which might cause other problems during the correction
>process, like make the edges of defects show up more than they wish) I
>would expect a certain amount of softening in the image when d.ICE was
>applied.
==========================================
Mark Thomas markthom@camtech.net.au
