Digital BW, The Print

Colin & Linda McKie writes:

> Anthony's statement (1) might be true in some fantasy land with
> scanners which can resolve twice the maximum possible detail/grain
> frequency, but in the real world some careful capture sharpening can
> compensate for the inevitable shortcomings of the scanning process.

No, it cannot.  No digital manipulation can increase the amount of
information in an image--whatever the scanner produces is all you will
ever get.  Furthermore, all sharpening algorithms produce image
degradation. Essentially, you trade real image information for an
illusion of sharpness: small details are actually destroyed in order to
emphasize larger details, which gives a visual impression of greater
sharpness even though the image is softened in reality.

Additionally, since sharpening must always be done with respect to the
type of output desired (photo printing, ink-jet, offset press, display,
etc.), no sharpening will serve for all purposes equally.

These two facts explain why sharpening must always be the _last_ step
before output of an image, and they also explain why images should not
be sharpened before being archived. Unsharpened scans might look soft to
you, but they contain more information and fewer artifacts than a
sharpened scan.

> Practical technology is so far from the theoretical ideal that
> achieving the right 'look' may be better than slavish adherence to the
> theory.

No, "practical technology" cannot violate the rules of information
theory. There is no sharpening method that does not degrade image
quality. This reality is one of the fundamental things that every
photographer must fully understand in order to get the best out of a
digital workflow.