(thing) by SharQ Sun Nov 04 2001 at 7:29:42

Introduction

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)

Scanner interfaces

  • 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 time)
  • 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:

  1. Scanner head (ccd)
  2. Scanner internal processing
  3. Scanner interface (i.e one of the five from the list above)
  4. TWAIN driver
  5. 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:

  1. You put a film strip or slide (or APS) in the scanner and scanning process is started (either via hardware1 or software2)
  2. A lamp3 is used to illuminate the thing in the scanner
  3. The CCD array moves across the film4 to make a pass. (the film goes between the light and the CCD array)
  4. 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.
  5. The captured image is processed and sent to the computer using one of the mentioned interfaces

1) via hardware: By pressing a button on the scanner
2) via software: By pressing a button on-screen saying something like "scan"
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.

Multi-scanning

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.

Scanner resolution

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?

  1. 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.
  2. Special Features
    • 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.
  3. Resolution
    • Obviously, the more information the scanner can get out of a picture, the better.
  4. Bit depth
    • 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).

Enjoy!

-30-

I like it! 2 C!s