On 05 Apr 2001 11:01:44 EDT Richard Starr (Richard.Starr@valley.net)
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.
Usually called 'contouring' (like a map) or 'posterisation' (like a poster
printed without contones).
You will be able to chack whether it is the file, or a problem with the
display/graphics system, by viewing the histogram. Contouring shows up as
missing bit values, leaving the histogram looking like a mangy dog's comb.
What file type is this, and what processing has been done (and by what) en
route to the screen? And what scanner/software?
If at any stage the file has been manipulated as an 8 bit file,
posterisation is easily possible. This can include adjustments within the
scanner driver, at acquisition time - especially if the s/w performs
adjustments after reduction to 8 bits from the scanner's native bit depth.
The more severe the adjustments (eg gamma), the more likely this is to
occur.
Regards
Tony Sleep
- Online portfolio & exhibit; + film scanner
info & comparisons
