Graphics Programs Reference
In-Depth Information
a different system, and yet the results were that the images previewed
differently on each system.
One solution was to calibrate the monitors on each system to a known
standard. Although this solved a significant problem, namely documents
looking different on each display, those calibrated displays still were
dealing with device-dependent color. Think of it this way: in order to get
two displays to match we may need to alter one display more than the
other. Therefore, the difference is inherently a condition of one of the
two devices. The actual preferences that described this display is now used
to produce RGB to CMYK conversions. All color space conversions
regardless of whether or not they use ICC profiles need two descriptors:
source and destination. In Photoshop 4.0 and earlier, the descriptor for
RGB was this monitor preference document, which likely did not accu-
rately describe the display system. Even if this document did accurately
describe the display, no two users would have identical monitor prefer-
ence files. If two users had the identical RGB document with identical
RGB numbers, the resulting color space conversions would not be iden-
tical. The source in both cases (Monitor RGB) was different so the desti-
nation values (CMYK) would be different. This was quite chaotic!
Photoshop's ICC Color Architecture
When time came to update Photoshop to version 5.0, Adobe made the
decision to revamp the applications color architecture to utilize ICC color
management. The issues surrounding the display and its role in pre-
viewing files was still a problem to be dealt with. The old monitor pref-
erence architecture was eliminated and replaced by an ICC profile that
described each user's individual display condition. However, the severe
limitations of using that descriptor for conversions had to be abandoned
for good reason: conversions had to be based upon something other than
the device-dependent nature of a unique display.
Adobe came up with a clever way in which to allow us to calibrate
our displays, yet still work with documents that were independent of our
individual displays. The specific condition of our displays would
not
be
used as an environment to edit our documents. Instead, Adobe would
provide some synthetic RGB color spaces into which we could convert
our documents for editing. These synthetic spaces are not based on any
real-world, physical device. Like LAB, these RGB working spaces are the-
oretical color spaces. Some spaces, like sRGB, are based on “average real-
world devices” (in this example a display derived from the HDTV
standard). Though the specifications of such a space are well defined, the
actual device behaviors of displays in reality are all over the map; we can't
assure that any two devices are even close to being identical. The problem
with devices, as we've discussed, is that each device is so unique. A display
system has specific idiosyncrasies as well as gamut limitations that can
cause problems when used to define a document's color for editing. Adobe
wanted to move away from editing files based upon the unique proper-
