Graphics Programs Reference
In-Depth Information
sions was all based upon a user's display system with no regard to the
final printing or output process. In the case of RGB images, the numbers
in the document simply were sent directly to the display for preview
purposes. As mentioned in Chapter 1, RGB as well as CMYK and
Grayscale documents are numbers, which alone don't fully describe how
the color should correctly appear. Sending the numbers directly to the
display didn't take this into account.
Prior to version 5.0, Photoshop had no idea what the numbers in our
documents really meant and had only a vague idea of the true condition
of our displays, even in the best-case scenario. An example was the han-
dling of a CMYK document. As previously mentioned in the last chapter,
CMYK is a highly device-dependent print/output color space. A CMYK
document by its very nature has been optimized for a specific CMYK
printer. To view a CMYK document in Adobe Photoshop 4.0 or earlier,
we needed to inform Photoshop, via its color preferences, the exact con-
dition of that CMYK. This was done via the
Separation Set-Up
and
Printing Inks Set-Up
preferences along with what was known as the
monitor preferences
file. This monitor preferences file was supposed to be
a description of the condition of our display, a concept somewhat similar
to today's use of ICC display profiles. Few users managed to produce an
accurate monitor preference file since hardware calibration in those days
was quite rare and rather expensive. Nonetheless, when configured prop-
erly, Photoshop could produce an on-the-fly CMYK-to-RGB conversion
for our display using this monitor preference.
Our monitors can display only RGB data, not CMYK data. Therefore,
some CMYK-to-RGB conversion has to be conducted for on-screen pre-
views. This fact is true today; however, the description of both the CMYK
data and the RGB behavior of the display are described using ICC device
profiles. A major limitation of Photoshop prior to version 5.0 was that if
a CMYK document being viewed differed in its color space described by
the user's CMYK preferences, the document would not preview properly.
There was a mismatch between the CMYK document and the actual
CMYK preference. Photoshop had no idea what the meaning of the
CMYK numbers were and made a guess based upon the current color
settings. This behavior isn't that different with current versions of Pho-
toshop; it still needs to know what the numbers in our documents are
supposed to represent using embedded ICC profiles.
Photoshop 4.0 and earlier assumed that every CMYK document
opened on a user's machine matched the CMYK preferences on that copy
of Photoshop. Worse, there was no way to inform the application
whether or not the CMYK document being opened was that specific
flavor of CMYK. No information was provided about how these docu-
ments were originally converted from RGB to CMYK. The same prob-
lems came when dealing with RGB and Grayscale files. It was common
for users moving documents from machine to machine to notice that the
color of their documents looked different on each monitor. The numbers
in those documents certainly didn't change by virtue of being loaded onto
