On 8/16/02 9:43 AM, "Preston Earle" <PEarle@triad.rr.com> wrote:
> As to the differences in ppi, dpi, spi, sspi, and other resolution
> issues, Dan Margulis has posted a chapter from his book "Professional
> Photoshop" at . I found
> it very informative.
Margulis makes a claim in this chapter that struck me as totally
counter-intuitive: sometimes a lower resolution scan will produce a better
looking output than one made at higher resolution.
The discussion of this issue starts in the last two paragraphs on page 278
of the above excerpt. An example is provided in Figure 14.9, which shows
two images of a horse standing on grass. The upper image was scanned at a
3x higher resolution, but the lower image looks sharper and clearer.
According to Margulis, the higher res scan produces an image with smoother
color variations, due to the statistical averaging in the downsampling
process. The lower res scan produces an image which more pixel-by-pixel
color variations, but this "noise" is seen as detail by our eyes.
But Margulis also notes that setting your scanner to use a lower resolution
may not provide any improvement. Some desktop scanners scan only at their
highest res setting, and then do downsampling in firmware or software. If
so, the damage is already done.
Very interesting. But I wonder if the loss of detail can be remedied by the
multistage sharpening/downsampling scheme that some people have been
advocating.
--
Julian Vrieslander <julianv@mindspring.com>
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