Negative
Scanning Instructions
Dale
Callaham
Central Microscopy Facility
University of Massachusetts, Amherst, MA 01003
Negative
Scanning Notes.
1)
For good quality and consistently exposed negatives it maybe possible
to skip
the preview and exposure adjustment steps, but with only an 8-bit data
output
range it can be difficult to get optimum exposure for all negatives
without
these steps.
2)
The user should experiment with resolution settings and saved-file type
in
order to be sure that the digitized output will suit the need. When
scanning as
described above, the output might be (typ.) 4464x4032 pixels and 1.5Mb
(as
jpeg) for a 4" x 3.75" EM negative.
The files are large, even as JPGs, but this is necessary to
capture all
the details of an EM negative. If your purpose only requires a
resolution such
as you might see on the computer screen (of a whole negative), then a
much
lower resolution will suffice, and will yield a much smaller file:
remember
that the file size increases by the square of the linear resolution.
But
remember, the lower resolution image for web or PowerPoint presentations
can always be generated from the
higher resolution image, but not the other way around. With the low
cost of
CD-R it makes sense to capture at full resolution, then put the
negative away
for safe keeping.
3) Saving
as
a JPG file compresses about 8-16x and
ordinarily results in an image that is nearly indistinguishable from a
tif
image. Remember JPEG compression is "lossy", and does not purport to
be able to perfectly restore the values or each pixel. Saving as a
compressed
TIFF image is another option. "jpeg-tiff" will essentially be a JPEG
compression inside a TIFF image format. The usual "compressed-tiff"
uses the LWZ compression engine and will faithfully reproduce the
values of
each pixel, but the output files are not as small as JPEGs and not as
generally supported by imaging applications. Both
compressed
TIFF formats are supported by Photoshop, Corel, and some other high-end
imaging
programs, but not all image display utilities know how to read them.
4)
The convention in the BCRC is to place your images in the
"Users_temp" folder on the "Local Disk". Create a
subdirectory named to a recognizable version of your user_name so that
it can
be known whose files these are.
5) Use
Fetch or other file transfer program (find it in the "Recent
Applications") to move the images off
to a server. You can leave your image on the machine, but don't expect
them to
stay there for long!