Integrity of Scientific Imagery:
Photoshop v.4 versus v.5

Michael Shaffer, University of Oregon

Having installed Photoshop 5 after using version 4 for
some time, I think that all scientists who believe that the integ-
rity of their imagery is important, understand what Photoshop 5
brings with it: the issue of "color space" or color profiles".
Whereas users could rely on the integrity of their image being
retained with Photoshop 4, this changes with version 5, and in
some cases rather severely. For example, a image bitmap
which might represent elemental spatial distribution data
should be considered to have a gamma of unity. Photoshop 4
would represent this data for editing via the display monitor's
gamma compensation only. That is, the integrity of the pixel
values would remain and visual compensation happens be-
tween data and display. Photoshop 5, on the other hand, will
modify pixel values in accordance with either a desired
"working" color space or an anticipated "target" color space.

A good example of this would be if version 4 is used to
create a linear gradient of grays. Examining the histogram
shows a fiat distribution of pixel values, 0 to 255. Now, if the
gradient is saved and loaded into version 5's default working
space {caveats below) and the histogram is examined, a very
different set of pixel values is found. If this file is now saved,
the original data is lost The degree of change is for the most
part moving from "simple data" (gamma=1) to a color space
gamma (gamma could be anything). The changes also reflect
color gamuts associated with either the display or the target,
but what is most noticeable is a compensation for gamma, for

which the default is 2.2.
Adobe has addressed this problem in the sense that the ear-

liest distributions of version 5 installed "color profiling" behind
your back without asking you to understand it. An available patch
(version 5.02) and current distributions now provide warnings,
and choices for defining the desired default color space or turning
it "off. Still, there are many virtues of color space if it is under-
stood. My message here shouldn't be considered as a suggestion
that every scientist should avoid Photoshop 5, just be aware of
this issue.

My suggestions would be to:
(1) Always keep the original image files intact.
(2) Keep the installation of Photoshop version 4,
(3) If version 4 isn't available, install only the latest distribution of
version 5.02, or install the patch (5 to 5.02) as soon as possible.
(4) Turn off "color space" conversion when opening files, and
use "profiling" only when a particular target color gamut and
gamma is desired.
(5) Do not rely on the manual for an understanding of color
space and profiles. Adobe provides much more information at
their web site:
http://www.adobe.com/supportservice/custsupport/TECHGUIDE/
PSHOP/main.html.

Also, investigate with the aid of 3rd party texts, such as Real
World Photoshop 5 (Addison-Wesley, 1999) by Bruce Fraser and
David Biatner, and Essentials of Digital Photography by Akira Ka-
sal, Russell Sparkman, and Elizabeth Hurley (New Riders Pub-
lishing, 1997). •

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