How to convert slides of herbarium specimens into good quality web site images?

Peter Rauch peterr at SOCRATES.BERKELEY.EDU
Fri Dec 15 11:27:40 CST 2000


On Fri, 15 Dec 2000, Diana Horton wrote:
> ... We tried
> scanning the slides using a Polaroid Sprint Scan (for
> slides), and the results were disappointing - the images
> were very fuzzy when blown up.  That presumably reflected
> the fact that they were scanned at 500 dpi;

Yes. That would not begin to capture the content of the film. To
get more close to the content of the film, you'd have to scan at
no less than 2000dpi, preferably more. And, you'd have to scan
at a color depth of 30bits or more, and your scanner should have
the ability to range over the black to white without losing the
details in one end or the other of the various densities.

Then, once you have captured the information from the photo
slide, you can play one of two (or both) games: compress the
scanned image, using either lossy or lossless compression
methods depending on just how much information you are willing
to tolerate and how small you wish to make the resulting
compressed file; crop the original high resolution scan into
several smaller hi-res images, compress lossless each of those
and post the lot to the web. This latter method will get you the
detail and quick download times, but of course, not the
full-sized image. ("Gee, I'd like to see those anthers in more
sharp detail", or "I'd like to see the flower on that bush more
closely" are good uses of the cropping technique.)

Some film scanners do the compression (lossless or lossy) on the
fly and deliver you an already-compressed file. If lossy, you
may lose detail that you'd prefer to have retained.

In summary, ...

> Can anyone tell me how to go from a slide image to a web
> image of comparable quality (i.e., sharp and clear,

Do high resolution scanning

> even if
> the viewer increases the magnification

Compress the images, preferably lossless to reduce download
time.

> ) that can be
> downloaded in a reasonable time frame?!

Crop those special ones that have particularly interesting
detail so as to retain the full scanned detail while
significantly decreasing download times.

Use a hand lens or dissecting microscope to examine the original
photos, to determine what portions of the image have detail
worth attempting to preserve by use of the above techniques.

Peter




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