Goleta DeskTop Publishing User Group
Meeting Information

August 2 -- Choosing a Scanner

OK, so it's time to get a scanner but the question is which one? The ads are full of information like "1200 x 2400ppi" and "32 bit color", but not at all full of the answer to the question "What do I need, and what will be the best for my purpose?"

I'll bring several scanners to demonstrate what some of those numbers mean, and it's not always bigger is better. For instance, a scanner that has 1200ppi resolution (yes, we'll define what that means at the meeting) gives you a much sharper image than one that has 600ppi, but it also is much slower. If you are scanning a manual that is going to be OCRed into editable text, the 600ppi will be a better choice.

But what if you have scads of 35mm slides that you inherited? How about the Epson 1640 Photo, with the 5" transparency head and costs only $350? ("Only" is relative -- $350 is cheap compared to a real film scanner.) Well, marketing being what it is, this scanner may give you 1600ppi of data, but not of information. What Epson did is use two 800ppi sensors and staggered them by a half pixel. The result is that the effective resolution of the scanner is much less than the 1600ppi that everyone expects from the model number or from the size of the data file.

Marketing also comes into play with the other numbers: some scanners have "32-bit internal color" or some such phraseology, but what they mean is that they don't hand all those bits to your picture editing program (PhotoShop, Paint Shop Pro, or whatever), but instead cram the data into 24 bits. There are some other scanners that actually *do* hand all the data to you, which gives you much more flexibility in dealing with over- or under-exposed images. Of course they usually cost more.

Then there're claims of "DMax" or "Dynamic Range" as if these are equivalent (which they aren't) and as if the numbers quoted are meaningful (which is rarely true). Many manufacturers look at how many bits they handle and claim they are all usable. But noise in the system often obscures the darkest parts of the scan rendering those last several bits useless. This is especially true in the blue channel.

More marketing: I have a scanner that claims the scan speed is 14.4 milliseconds per line, so at 1200ppi I would calculate that it would take 17.3 seconds per inch, or about 70 seconds to scan a 4" high image (like a 4" x 6" print). Of course the real scan time is more like 2.5 minutes. No, the difference is not due to the amount of time it takes the scan head to return to the starting position.

Come to the meeting and see a comparison of several flatbed and 35mm film scanners, and learn what the tradeoffs are. Then you will know what questions to ask the salespeople and will be able to make a more informed choice about which scanner(s) to buy.

Please send email to gdtpug@troutcom.com with suggestions for topics you are interested in seeing covered. Or even better, volunteer to give a presentation!

The Goleta DeskTop Publishing Users Group is a SIG (Special Interest Group) of the Santa Barbara PC Users Group. We are not platform specific: some members have PCs, some have Macs, some have both. Linux and other systems are sprinkled in as well for good measure. We focus on the issues of publishing in all forms, be it on paper, web, CD-ROM, or some other medium.