digital images

Timothy Rowe rowe at MAIL.UTEXAS.EDU
Tue Aug 22 12:52:30 CDT 1995

The major quality difference that I have encountered between video and film
is depth of field.  With film, one can shoot focused images of objects that
have great depth, by closing down the camera aperture and increase the
exposure time. That is, film offers the capacity to vary the depth of field
in focus when making a photo.  Video has nothing comparable to this - there
is only a shallow, invariable depth of field.  If you are imaging a deep
object, like the occlusal surface of a mammalian tooth crown, only part of
the crown will be in focus in a video image.  Even using high-resolution
frame grabbers (video _per se_ is limited to about 500 lines of resolution,
whereas high-resolution grabbers can exceed 2000 lines for any given image
field) there is no way that I have encountered to gain depth of field.
Moreover, with the higher resolution frame grabbers, as in higher
microscopal magnifications, the small depth of the field provided by the
instrument decreases compared to the depth of (low-resolution) video
imagery.  Digital processing of a blurred image is a labor-intensive and
ultimately a poor substitute for the depth of field offered by film.

Having a functional video imaging system, I take take a lot more video
images than photographs.  Video is never quite as good as film, but because
it offers "instant gratification" and an acceptable image at low cost, I
have migrated to this technique. The quality of the lens on the video camera
is of paramount importance -- a low resolution 1-chip CCD video camera
(i.e., a cheap camera) mounted on a fine zoom microscope will produce superb
imagery.  However, if I need a fine, focused image of an object that has
depth, I have found no alternative to first photographing the object and
then scanning the film.

Other issues to consider in choosing between video and film involve the
costs of video/computer/storage equipment vs. costs of film/processing.

If your goal is to widely distribute the imagery, then the images will have
to wind up in digital form in the end.  In my opinion, the ideal system for
imaging museum specimens will include a conventional cameral and lighting
system, and a CCD video camera (along with a computer), and a variety of
lenses (conventional lenses and microscopes).  You'll also need a pathway to
digitize the film thatyou do shoot. I prefer a 35mm digital slide scanner
(now under $2000) over Kodak's commercial scanning service (Kodak will scan
film and dump it to CD-ROM at low cost), because the commercial services
make a lot of errors in image orientation, cropping, contrast, and color
palette.  You'll also need a big hard drive and a second backup device.
Lastly, you'll need some means to distribut the imagery, such as a CD-ROM
writer or an Internet server.

Timothy Rowe
Department of Geological Sciences and
Vertebrate Paleontology and Radiocarbon Laboratory
The University of Texas at Austin
Austin, Texas 78712

phone: 512-471-1725
fax: 512-471-9425

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