P3D Re: Scanned image from Stereo World (Test results)

[Lee Moore <moore@xxxxxxxxxxxxx>]

I measured the halftones in the last Stereo World.  The magazine
uses a 45 degree screen that runs about 165-170 lines/inch.  The
duotone on the cover has a black seperation at 45 degrees and
a orange seperation at 15 degrees.

If we invert the rule-of-thumb that one should scan a continuous
tone image at twice the screen frequency that used in printing,
then we should scan the images in Stereo World at 330 to 340 
spots/inch to retain all the information.

I have worked on various document scanning projects and the
hard question that must be understood in advance is:
    What is the user going to with the data?
Obvious there is a cost to scanning at a high resolution
than necessary.  The danger of scanning at a lower resolution
is scarificed quality for some applications.  In most cases,
the labor of actually doing the scanning dictates that you
only want to do it once.  Thus it is wise to scan at the
highest resolution that is practical and down sample later
if you don't need the information for some purpose (like
web display).

There are also issues with representing gray levels.  On my
Sun monitor, the sample scan didn't have good detail
in the shadow regions.  We should try to preserve the tonal
range from the scans.  Some scanning software returns images
with implied gamma correction for some monitors. 


--
Lee Moore  /   Xerox Digital Imaging Technology Center
 Webster, NY  USA   43.219601 N, 77.419401 W


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