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Greetings!
Much of what we do in many areas of forensics is by
nature a destructive process. This means that the
process of collecting or analyzing evidence will
often change something about that evidence that
cannot be recovered. An example of this is
processing a sheet of paper with ninhydrin for
fingerprints. This process can cause inks to fade or
run, and will cause purple stains to appear as the
ninhydrin reacts with amino acids of the latent print.
Working with digital images can be a nondestructive
process. We can make exact digital copies
of our original files and maintain these as archival
images that will never be changed. We can also make
many adjustments to our
working copy that will not change the pixel values
of our base image layer. Both of these aspects
represent a nondestructive workflow for digital images.
In this issue of the Resolution Video Newsletter, we
feature an article written by George Reis of
Imaging
Forensics on working nondestructively in Adobe
Photoshop.
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| Nondestructive Processes in Adobe Photoshop |
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Adjustment layers are key in working
non-destructively with digital images. These layers
do not change the base pixel values, they can be
applied globally or locally, they are re-editable,
and they can be applied to multiple images.
To apply an adjustment layer in Adobe Photoshop CS2,
simply choose Layer > New Adjustment Layer, and then
choose the type of adjustment layer you want to
apply. You can also access this from the New
Adjustment Layer icon at the bottom of the Layers
Palette. When you apply the adjustment, the image
takes on the appropriate appearance, but a new layer
is also created. If you uncheck the visibility icon
for this layer, the original pixel values are
displayed; check it, and the adjustment shows.
Double click on the Adjustment Layer and you can
verify your settings or re-edit them. The attached
mask allows one to make the changes on a local part
of the image in a repeatable and verifiable way.
Multiple adjustment layers can be applied to the
image, and their order can be changed as appropriate.
Filters can also be applied without changing the
base pixels values but with fewer capabilities. This
is done by applying the filter to a new layer. If
your image only has a single layer, this is done by
selecting it, then choosing Layer > Duplicate Layer,
or pressing Cntrl-J on your keyboard. If there are
adjustment layers, be sure the visibility is on for
all layers, select the top layer in the group, and
press Cntrl-Alt-Shift-E (pre-CS2, use
Cntrl-Alt-Shift-N-E). This creates a new layer and
stamps the visible layers into that new layer. Now
apply the filter, and the original pixel values are
still intact on the base layer.
As a final step, rename the layers with the name of
the tool and the settings applied. The final image
will have multiple layers - the base layer has the
original pixels, each layer above represents an
adjustment or filter, and good naming conventions
that show at a glance exactly what was applied.
During Resolution Video's
class, Basic Forensic Digital Imaging, a
variety of nondestructive processes are
demonstrated and practiced. For more information on
this class,
including a class syllabus and location information,
click
here.
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| Scientific and Technical Imaging Association (STIA) |
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The Scientific and Technical Imaging Association
(STIA) is a new organization for imaging
professionals working in the technical and
scientific fields of imaging. These fields include
academics, aerospace, archaeology, astronomy,
engineering, forensics, machine vision, medicine,
photogrammetry, research, and related technical and
scientific disciplines. And, the work includes
photography, image processing and analysis, and
related areas.
The goal of this organization is to share
information and create training opportunities
through cross disciplines that share a scientific or
technical commonality in their work. It is not the
goal of this organization to replace any existing
association, but rather to provide an additional
resource to complement existing professional imaging
organizations.
STIA will provide a newsletter, training, a web
forum and other resources to its members with state
of the art information on imaging issues related to
our fields. STIA is an umbrella organization
building cohesiveness among several imaging
disciplines with a commonality in science or technology.
For more information, general inquiries, or to take
an on-line survey to shape the organization, please
check out their website at www.scitechimaging.org
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