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Re: filmscanners: ColorSteps?
Richard Starr wrote:
> I don't know if color steps is the right term but it seems to be a display
> problem. In several high resolution scans, I've seen some odd areas of color
> that should be continuous appear to step from one tone to another as though
> displayed in 256 colors or fewer. One was a reflective surface with some
> specualr highlighs (a polished truck fender) and another was may daughter's
> softly lit cheek. It's a high res 24 bit Photoshop display on the Mac, on a
> Sony Trinitron monitor. I was thinking there was somthing odd about my
> scanner, but the colors are smooth and continuous in the Epson print.
> One example is from an Ektachrome slide, the other from a high speed negative
> film. I thought of the grain aliasing discussed on the list, but I'm not sure
> what it looks like. It appears in all zoom settings of the display, so
> with scan lines wouldn't explain it.
> In the display it almost looks like the kind of color reversal you can get
> you bend a curve too far. It don't show in the print though... weird.
> Any ideas?
This type of posterization can be caused by a number of things like
display card problems (often drivers) by a monitor with non-linear color
steps, (sometimes adjustable in firmware, depending upon the monitor).
Sometimes, I have actually seen this on film (most often Kodachrome) on
highlighted areas. The Epson may be "fixing" this problem with some of
its driver software, also.
Try rescanning at a slightly more carefully corrected white point, you
may be running against the wall of the scanners accuracy at the very top
of its range. If the scanner is outputting only 8 bits, this could
easily be errors in bit accuracy, in which case the best thing might be
to scan slightly darker and then adjust a bit in Photoshop (a compromise).