[filmscanners] Re: Correct/best methods of scanning

["Tony Terlecki" <ajt@mrps.demon.co.uk>]

On Mon, Dec 09, 2002 at 01:32:53PM +0100, Roger Eritja wrote:
>
> >The question is: Is a better image produced from one method than the other?
> >Is it wrong to have a large file then scale down? Or is the image slightly
> >sharper, better resolved (or whatever the correct terminology may be...),
> >any thoughts? Ideas? Anyone produced any tests?
>
> This a very interesting issue and I was just thinking about raising it to
> the list, as we are having an enriching discussion between photographers
> here. Some friends say that scanning must be done to the exact final size,
> because every resampling is destructive. As an example, one of them called
> for scanning a pure black, thick line drawn on a pure white background, and
> then resample/downsize via bicubic or whatever: the borders turn grey,
> which is a color not present in the original image. He concluded that
> downsizing blends colours and creates artifacts (but, since he's operating
> an Imacon Flextight maybe he doesn't really need to increase detail).
>
> Other colleagues are scanning at maximum resolution -to capture all the
> detail the scanner can resolve- and downsizing later. Here, the point is to
> apply some techniques recently discussed on the list via wise sharpening
> filters between resizings.
>
> I have carried out several simple on-screen tests with my LS4000 and
> couldn't really tell a difference, but again this might be tested on large
> printed copies. Any thoughts from the real experts here?
>

As usual there are many factors involved and you will find that many answers
are very scanner/software specific. Everyone should really do their own tests
to determine what works for them for any particular type of image.

Some scanners will scan at full optical resolution regardless of the
resolution you ask for and then downsize in software. With this method you
are at the mercy of the software's downsizing algorithms. They may be good
but you also may be better served by resampling using your preferred software.

Other scanners may scan at lower resolutions by scanning every second or
third line (or whatever is nearest and just above the requested resolution)
and then downsize from there. Again this might not be optimal since some
detail in the scanning lines that was missed may be significant.

If I were to play it safe I would always scan at full optical resolution and
then play around with different resampling algorithms to see which one gave
me the desired result. Although Photoshop uses bi-cubic interpolation as
default there are many other algorithms which don't cause unpleasant
blending at sharply defined edges. Nearest-neighbor is one from PS that springs 
to
mind. Each algorithm will have its own strengths and weaknesses.

--
Tony Terlecki
ajt@mrps.demon.co.uk

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