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[filmscanners] Re: JPG sharpening [was: Color spaces for different purposes]



Ken writes:

> When I scan an image - into whatever file
> formet, I use TIFF out of Vuescan - and then
> open it in PS, I can immediately see some
> sharpness loss ...

As compared to what?

When I've compared scans to actual direct examination of negatives or slides
(Provia and Velvia) under a microscope, I often cannot see any clear
difference at all, at least at 4000 dpi.  When you look at a scan on the
screen, at full resolution, you are looking at the equivalent of a huge
enlargement; MF scans at 4000 dpi displayed on my screen (which is set to
1600x1200), for example, are the equivalent of an enlargement measuring 7.5
feet on a side.  Scans that large will not look sharp unless you used a good
lens, a sharp film (Provia, Velvia, Kodachrome, etc.), and a tripod.

> It's in the down-sized scan that I see the change
> in sharpening response.

The sharper the original transitions in an image, the greater the apparent
effect of an unsharp mask tends to be.

> ... why is the sharpening so much more effective
> on the smaller image?

There are more details in the smaller image for a given number of pixels,
and they are spaced more tightly.  The nature of sharpening is such that it
is much more obvious when an image already contains a lot of fine detail.

> And am I losing something I'm not yet aware of?

When you downsize, you lose a great deal of detail; which is why you cannot
upsize again and get an image identical to the original.

> 2 examples - feel free to criticize:

They look great, just right.  I don't see any artifacts.

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