I'm looking to by a film scanner and I really want one that provides superb quality. I've been comparing a few different scanners off of this web site and I've noticed a visible difference in the quality of some of them. The Minolta Dimage Scan Dual that lists for $500 and has an "8 bit" depth. While viewing the sample image of the "Train" shot taken with this scanner, I found the image had edges that seemed a little jagged. Also there appeared to be a lot of "noise", especially in the dark part of the train.

However, when I looked at the same train picture that was taken with the Minolta Dimage Speed Scan that sells for $1299 with a "12" bit color depth, I didn't notice any jagged edges, and the noise was considerably less visible to me.

My question is, is the difference between the 8 bit color depth and the 12 bit color depth the main reason for these differences in picture quality? If they aren't, what is?

Thanks

Jim

-- Jim Shields (JimShields@Worldnet.att.net), February 17, 2000

Answers

The difference between 8 and 12 bit output is relatively significant. 8 bit analog to digital conversion means that for each channel in a color image (Red, Green or Blue), there are 256 gradations between black and white. 12 bit there are 4096 gradations, so the contrast between neighboring pixels is far less in 12 bit vs. 8 bit, so things like noise and the "jagged edge" appearance are enhanced in the 8 bit vs.the 12.

I own a Scan Speed, and it is a wonderful machine. I regular use it for web output as well as Luminage printing up to 16X20 with outstanding results.

-- Jason Kirk (jasonkirkphoto@hotmail.com), February 18, 2000.

The "jaggies" in the Scan Dual train pic aren't a function of bit-depth. It's more likely that they're due to an inferior interpolation algorithm, or a jerky, possibly faulty scanning mechanism. If you look closely at the full resolution scans of the girl's face, on Ed Hamrick's site, you'll see vertical striations on some of them. Could it be that some of these high-priced scanners ain't all they're cracked up to be? Draw your own conclusions. Bit-depth is important though. 10 bits doesn't give much leeway for slides with a wider than normal tonal range, or overcoming the mask on colour negatives. Personally, I wouldn't even consider a scanner with less than 12 bits per channel A/D, and preferably one with the ability to export all those bits to an image-editor.

-- Pete Andrews (p.l.andrews@bham.ac.uk), February 21, 2000.