Drum vs Flat-bed scanners
Drum vs Flat-bed scanners
- Subject: Drum vs Flat-bed scanners
- From: Don Hutcheson <email@hidden>
- Date: Sat, 01 Sep 2001 11:27:21 -0400
Watching Randy and Andrew's exchange spurs me to clarify the real difference
between drum and flat-bed scanners, and to suggest a third category for the
Flex-Tight.
A true drum scanner can also be called a 'flying-spot' scanner, whereas flat
bed scanners - and the FlexTight - are really 'line-at-a-time' scanners.
True 'drum' scanners illuminate the original with a tiny spot of light,
which effectively flys across the original (even though we know the original
is really moving.) Flat bed scanners - and the FlexTight - illuminate the
original with a whole line of light at a time that lights up a long thin
strip of the original. And for the record, hand-held digital cameras and
camcorders are 'field' scanners because they scan a whole 2-dimensional
field at once.
In this context the FlexTight is much more akin to a flat bed scanner than a
true drum scanner. The 'drum' claim is just marketing. If you must
categorize it by the shape of the original, I would call the FlexTight a
'bent-bed' scanner, but it is still a 'line-at-a-time', not a 'flying-spot'
scanner.
The disadvantage of line-at-a-time illumination (or field-at-a-time
illumination, for that matter) is that light from a bright area of the
original can be scattered by impurities or dust in the optical components -
or air itself - into darker areas of the image. A true drum scanner
completely eliminates this type of large-scale optical flare, producing a
'cleaner' sampling of extremely dark image detail.
Where this optical flare really shows up is in under-exposed originals where
a lot of lightening must be applied to the scan. With normal originals the
flare is usually too small to matter, unless the optics are very dirty. But
when opening up really dark originals you see a ghosting around bright areas
that seems to extend in one direction but not the other. This is the mark of
line-scan flare. People Magazine discovered this dramatically a couple of
years back when trying to save a very under-exposed chrome of Ivana Trump.
Scanned on a Scitex EverSmart it was ok, but shadow areas looked uneven and
smokey. Re-scanned on a Hell 3900 it opened up perfectly with smooth and
neutral shadows.
Don't confuse this with shadow sensitivity. Most good flat bed scanners
today are actually BETTER than most drum scanners at digging out shadow
detail, at least on a gray scale, but that detail is usually unstable and
hard to profile due to the unpredictable effects of image-dependent flare.
And don't just assume that any drum scanner has acceptable shadow
sensitivity. Test it before you buy by scanning a long-range neutral density
transparent gray scale. (See 'Scanning Guide 2000' at
www.hutchcolor.com/CMS_notes.html). The best I've seen is the ICG 360i, but
ONLY with the very latest software improvement. If you have an ICG ask about
getting the upgrade. Beats anything I've seen on any Hell (Heidelberg) or
Crosfield (Fuji) drum scanner.
Although flat bed scanning technology has improved amazingly over the last
twenty years, when it comes to opening up really dark originals I'd still
choose a good drum scanner any day over the best flat bed - including the
FlexTight.
Don
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Don Hutcheson
Hutcheson Consulting
(Color Management Solutions)
Phone: (908) 689 7403
Mobile: (908) 500 0341
email@hidden
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