Snap logic tells me that downsampling an image should not degrade that image in any way, but is that the real story? Get theoretical if necessary and help me put this to rest.
Dale:
Downsampling can be done in a number of ways, but all of them do degrade the image in some way, shape or fashion. Much of it simply has to do with the "rounding" that occurs when you take a larger number of values and take the average of them to determine the component value.
Think of a set of 9 pixels with the following values (1 to 9 to keep it simple)
5 4 5 4 1 5 4 4 6
If the image is downsampled sufficiently to require that the average value of the 9 pixels now be represented by 1, then I think it's safe to say that in this case it's not going to be 1 or 6, the highest or lowest value. On a grand scale this is going to have a smoothing effect on the whole image, and the result will be an image with "less variation" which I think could reasonably be construed as degradation.
This is why many photographers use a form of "stairstep" downsampling to "crisp" up an image before the averaging smooths out the variations. See http://ControlledVocabulary.com/imagedatabases/downsampling.html for my take on this procedure.
There are times where this smoothing may be desirable, but if the end result is printing via 4-color offset, smoothing typically yields mushy images, not sharp ones.
Hope that helps.
David
David Riecks (that's "i" before "e", but the "e" is silent) [EMAIL PROTECTED] http://www.riecks.com/ Midwest/Chicago ASMP * ph/fax 877-646-5375
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