A Film scanner is a scanner that scans photographic film, i.e negatives,
positives (slides), in some format or another (i.e APS,
135, 110, 220 etc) for use on the computer.
Film scanners are pretty much for photographers - a decent film scanner costs
the same as a decent camera... But hey - that doesn't stop me from doing a writeup
on them, right?
Film scanners are usually made by manufacturers of camera equipment, instead
of manufacturers of computer equipment. This is an important difference, and
pretty much explains the difference in price (and, obviously, target market)
- Parallel - For film scanners, I can only think of one that uses
it. And trust me, you don't want it.
- USB - With a few of the simpler, budget model film scanners, you
get USB (Universal Serial Bus) connectivity.. However, you usually
have to go for...
- SCSI (Small Computer System Interface)- This is the main interface
for film scanners. For PC users, this often means installing an extra card,
but don't let that scare you - although SCSI can be an evil bitch to install,
it is fast, which is a good thing with the file sizes you will be operating
with. (USB 2.0 or Firewire will probably take over with
- Firewire (or IEEE 1394) - Firewire is basically a very
fast USB, and is therefore used in a few film scanners.
The information between a computer and a scanner goes something like this:
- Scanner head (ccd)
- Scanner internal processing
- Scanner interface (i.e one of the five from the list above)
- TWAIN driver
- Program (i.e MS Word, Photoshop or whatever)
The TWAIN step above is important, because this is what enables the computer
to communicate with a scanner. In general, TWAIN helps scanner vendors to write
device drivers for their products.
How a scanner works
The most important part of the scanner is the CCD unit. (for an absolutely
fabulous description about how CCD's work, have a peek at my writeup on
the subject. Even though that was written for digital cameras, the same applies
for scanners. Just substitute "digital camera" with "scanner",
and ignore all occurences of "megapixel"). The CCD, in short, is
the "eye" of the scanner.
What happens when the scanner scans:
- You put a film strip or slide (or APS) in the scanner and scanning process
is started (either via hardware1 or software2)
- A lamp3 is used to illuminate the thing in the scanner
- The CCD array moves across the film4 to make a pass. (the film
goes between the light and the CCD array)
- The light from the lamp goes through the film. It then goes via a set of
mirrors (usually 2-3 mirrors) to the CCD array.
- The captured image is processed and sent to the computer using one of the
1) via hardware: By pressing a button on the scanner
2) via software: By pressing a button on-screen saying something
3) The lamps used in film scanners are usually Xenon lamps, of
extremely high quality
4) Some scanners don't have a moving array. Instead, the CCD is fixed,
and a mirror moves to reflect the information into the CCD array.
Some scanners (usually high-end models) use a Multi-scan feature to can scan
one frame multiple times (typically 4 or 16 times scanned in one slow pass).
Those images are combined into one image, to average out the random scanner
noise in the image data. It is an important noise reduction technique to produce
clean dark tones from slides Multi-Scan is not such an advantage for negatives,
because negative dark tones are inverted to the highlights where the noise
is harder to see.
Film scanners are of much higher resolution than flatbed scanners
- usually somewhere between 2400 dpi and 4800 dpi. Because film scanners
are aimed at professional users, they are hardly ever marketed with their interpolated
resolution - if you find one that does, you're probably better
off avoiding it
Bit Depth / Colour depth
This is a number referring to how many colours a scanner can reproduce. In
the table below, you see a few of the normal color resolutions for film scanners.
BPC | BD | COLORS
10 | 30 | 1,073,741,824
11 | 33 | 8,589,934,592
12 | 36 | 68,719,476,736
13 | 39 | 549,755,813,888
14 | 42 | 4,398,046,511,104
15 | 45 | 35,184,372,088,832
16 | 48 | 281,474,976,710,656
BPC= BITS PER CHANNEL
BD = BIT DEPTH
as you can see, the bit depths increase with increments of three (because an
increase of one bit per channel of each of the RGB color amounts to a three
bit color depth increase), and the number of colours increases exponentially.
Adobe Photoshop can't handle more than 48 bits, so chances that we'll see
images with higher bit rates than this are small. On the other hand - the human
eye is a forgiving tool - and will never need that many colours anyway.
What determines what is a "good" scanner?
- Scanner software
- Believe it or not, but scanner software and firmware are the most
important factors in scanner quality, and for film scanners, that is even
more so. In fact, the differences are so big, that there is big business
in making better scanner drivers than the manufacturers make themselves.
Most prominent in this is Silverfast, which is a program that is said
to improve the quality of the scans drastically.
- Some scanners do multi-pass scanning.. If you scan lots of slides (as
opposed to negatives), this is probably a good idea
- Digital ICE (Digital Image Correction and Enhancement) is a feature that
comes with Nikon film scanners that removes scratches and dust from negatives.
- Obviously, the more information the scanner can get out of a picture,
- The more colours, the more you have to work with. (you'll never be able
to put all those colours to use anyway :)
How to choose a scanner?
Find out what you need. If you are going to use the scanner to scan holiday
snaps and send it off to friends via the internet or put them on your web page,
don't bother getting a film scanner. Get a flatbed scanner with a dias
option, and scan your negatives like that. Or even better: Scan the paper copies.
For more serious work ((photo editing, archieving images digitally etc),
first sit down, and realize you are about to spend some serious money. Then,
consider one of the medium-range models from Nikon, Minolta or Polaroid
(or basically any other brand that makes your wallet hurt).