Gitchigumi Loc: Wake Forest, NC

(Sorry, the title got messed up) This relates to digital scanners... Service vendors offer 3,000 to 5,000 dpi resolution when scanning slides or negatives. And, yet, there are flat bed scanners that claim 9600 dpi. So, how can dedicated slide scanning equipment not offer as high a resolution? Or, are not all dpi claims reporting "apples to apples"?

lamiaceae Loc: San Luis Obispo County, CA

You'll get likely a ton of replies. Some actually will know what they are talking about. Right off, digital resolution is in ppi, optical resolution (lenses) is in (lines per inch) lpi, and printing & scanning resolution is in (dots of ink per inch) dpi. Printer and scanner manufacturers often mix or interchange terms either confusingly or incorrectly. They are not equivalent.

It is kind of like converting Kilocalories to Watts, they are similar but one is Heat Energy and the other is Work. The numbers are not the same.

You probably do not really want super high scanning rates. As you scan at rates higher than 300 or 450 the files get huge (larger than your camera's RAW files), and the scanning times can approach 30 minutes! Imagine scanning 100 Negatives! The super high resolution is probably OK for one or two special images.

Before I had a scanner I would (copy) photograph negatives and slides with a digital camera. In fact I still do that for 4x5" and larger films as my scanner and most do not do over 6x9cm film strips.

Someone on the UHH with more patients than I will give you enough info to make your head spin. We actually have a member or two that are in the Printing business.

Gitchigumi Loc: Wake Forest, NC

Thanks for your insight, lamiaceae. And, as I read more about slide scanning, I see where the providers say that going higher than, say, 6000 dpi actually introduces noise. And, that degrades the IQ. So, that seems to be the limiting factor: precision, but not enough to lose quality.

CPR Loc: Nature Coast of Florida

The density of the scanned image breaks down to the number of bits of information per inch of image. Scanner (and printer) references are usually dpi (dots per inch) since they are dealing with physical paper. Each dot is represented by at least a byte of data, so if you scan at 300dpi and you scan 4 inches you get 1200 bytes across then if you scan 300 lines horizontally you get 300 X 1200 or 360,000 bytes of data for a 4" X 1" strip. You can reduce that data storage if you save the file in a format like jpg that compacts the data. The more dpi the more detail captured.
I restored a 1 1/2 inch square 75 year old picture and went to 2400 dpi and it took a looooooong time but I had the detail needed to end up with a decent 3"X5" print. An 11" X 17" framed print was fine at 300dpi.
The key being what you start with and what you want to end up with.

Gitchigumi Loc: Wake Forest, NC

The service provider I am looking at has the Nikon Super CoolScan 9000, which can scan slides at 4000 dpi "True Optical Resolution" in about 40 seconds. Production scanning would require such speed. Time is money! In answer to my own question, though... it seems that dpi = dpi. There are various reasons for utilizing different levels of precision, however. The basic unit of measure, dpi, isn't different from one usage to another. That is the bottomline.

SalvageDiver Loc: Huntington Beach CA

Hi Gitchigumi,

As one who had scanned many negatives and slides, I ultimately had to resolve this very question. The responses you received are spot on. Pixel resolution and optical resolution are very different, just as in cameras. For example, if you had a 50mp camera will a poor lens or poor focusing system, you'll get a large but blurry file. Here is a very good site that explains the differences and provide test results on a variety of flatbed and film scanners, including the LS9000.

http://www.filmscanner.info/en/NikonSuperCoolscan9000ED.html

Mike

Gitchigumi Loc: Wake Forest, NC

Thanks for that! At present, I am leaning toward a service-provider for this work. And, they use the Nikon 9000 scanner. Now, the task is to sort all the slides and negatives and see how many I want to get done.

SalvageDiver Loc: Huntington Beach CA

good luck, that's always the most difficult part

Gitchigumi Loc: Wake Forest, NC

Thanks!

Architect1776 Loc: In my mind

Epson V750 is 6400x9600 DPI.
But there are limits as to what can be scanned at that setting.