Re: filmscanners: ColorSteps?

[Arthur Entlich <artistic@ampsc.com>]

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 
>antique
> 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 
>aliasing
> with scan lines wouldn't explain it.
> 
> In the display it almost looks like the kind of color reversal you can get 
>when
> you bend a curve too far.  It don't show in the print though... weird.
> 
> Any ideas?
> 
> Rich

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).


Art
Art