[SATLUG] OT - photo scanning services

Brad Knowles brad at shub-internet.org
Fri May 30 14:51:44 CDT 2008


Mark McCoy wrote:

> Also, these are standard 4x6 prints taken over the last 20 years, what would
> be a good resolution to scan them as?  I have seen several services online
> offering 300, 400, and even 600 dpi (for increasing costs), but I wonder
> which would be the best resolution.

I was going to give you an answer based on my experience of what the devices 
are capable of, but then I did a bit more research and found the answer is 
actually a lot simpler -- if you're scanning from color or B&W prints, in 
most cases you're not going to see any more detail if you scan them at more 
than 300 dpi.  You can probably scan them at 200 dpi and lose little or nothing.

If you can get the original negatives, those can be usefully scanned all the 
way down to 3000-4000 dpi, but not the prints.  The problem is that the 
paper just loses way too much of the picture information that is recorded in 
the negative.  There's just no sense in scanning color or B&W prints at much 
above 300 dpi.

See <http://www.scantips.com/basics08.html> for more info on scanning 
prints.  See <http://www.scantips.com/basics12.html> and 
<http://www.scantips.com/basics13.html> for more info on scanning film and 
negatives.

In fact, the whole scantips.com page has got lots of useful info.


Color depth and dynamic range are also important.  A $50 cheapie scanner 
might technically be able to do 600 dpi, but will probably have really 
crappy dynamic range, which would make the resulting scans look horrible.  A 
good quality scanner will get you a Drange of 2.5-3.0 or better, depending 
on whether you're scanning color or B&W photos.

Also, don't be fooled by a high Dmax number, if the Dmin number is also high 
-- in those cases, you'd get great shadow detail but all your highlights 
would be blown out.  You want a good Drange (Dmax minus Dmin), but ideally 
you want a Dmin as close to 0.0 as you can get (so it doesn't blow out any 
highlights).




It's also useful to have a scanner with an A/D converter that has more than 
just 8 bits.  Your eye won't be able to perceive the additional bits of 
data, but what this will do for you is make the higher eight bits of the 
data much cleaner, and the fact that the lower bits are noisy is not a 
problem -- especially if you're going to be doing any manipulation in 
Photoshop in a mode that allows more than eight bits per color.

See <http://www.scantips.com/basics14.html>.

I found some other good pages at 
<http://www.kenrockwell.com/tech/scantek.htm>, 
<http://elbereth.obspm.fr/~kervella/Scanners/dmax.htm>, 
<http://photo.net/learn/drange/>, 
<http://www.auspiciousdragon.net/photowords/?p=1063> that discuss issues 
regarding dynamic range, Dmax/Dmin, etc....


Then there's the issue of color calibration.  It doesn't do any good to scan 
the pictures at the proper resolution if everyone looks like a Green Orion 
Slave, or a Red Denebian Slime Devil because the color calibration is way off.

Some of the issues are discussed at <http://www.scantips.com/basics15.html>, 
but see also 
<http://desktoppub.about.com/cs/colorcalibration/a/cal_scanner.htm> and 
<http://www.normankoren.com/makingfineprints1A.html>.

Keep in mind that you need to calibrate the scanner, your monitor, and your 
printer, and you need to periodically go back and re-calibrate them to make 
sure that any color shifts over time are detected and compensated for.  And 
you'll need to have good color management system software on your computer 
to handle all the calibrated profiles that you've got and properly apply them.

>                                      I do intend to have some of these
> reprinted eventually (a physical photo album is still nice to have), and I
> want to ensure that they will still look nice after reprinting.  My scanner
> is OK, but I don't want to sit for a week scanning pictures unless I have
> to  :) , only to find out that I didn't scan them at a high enough
> resolution.

Get them scanned at 300 dpi on a good quality scanner that has a good Drange 
and a Dmin as close to 0.0 as you can get, and fully color calibrated, and 
that will be about the best you can reasonably expect to get.

-- 
Brad Knowles <brad at shub-internet.org>
LinkedIn Profile: <http://tinyurl.com/y8kpxu>


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