Graphics Programs Reference
In-Depth Information
Working Spaces Up Close
Let's look at working spaces a bit more before we move on. The name
working space is a term invented by Adobe to describe a class of a color
spaces that are designated for editing our images. Photoshop uses the
term working space in many areas in the application such as in the color
preferences when configuring the color settings for RGB, CMYK, and
Grayscale documents. Although there are RGB, CMYK, and Grayscale
working spaces, the role of the RGB working space is the one that con-
fused many users and is a bit different from CMYK and Grayscale working
spaces. CMYK and Grayscale color spaces are intended primarily for
output (printing, perhaps viewing on screen). The RGB working spaces
provided by Photoshop are synthetic, mathematical constructions. In fact,
for a time, I used to call these RGB working spaces
Quasi-Device-
Independent
until my technical editor, a true color scientist, asked me to
refrain from the practice.
Color scientists can correctly argue that the RGB color model can't
behave as a device-independent color space even if you put the word
“quasi” in front of it. The idea is that although these RGB working spaces
by their very nature cannot be device-independent, these spaces are
not based on any individual RGB input or output device. Some of the
RGB working spaces (such as sRGB) are based on a standard descrip-
tion of a device such as an HDTV display using exacting specifications in
a specific environment. Therefore, even though some RGB working
spaces are supposed to be based on the behavior of a certain “average
real-world device,” the exacting mathematical constructs that describe
these color spaces are fixed, which is why RGB working spaces are
useful.
These synthetic RGB working spaces share one common and very
useful attribute. When red, green, and blue are all equal values, such as
R123/G123/B123, those numbers will always produce a neutral color!
This behavior is sometimes referred to as
well-behaved
. RGB color spaces
from input devices with identical values of RGB are not necessarily
neutral and it's very unlikely that a print/output RGB color space would
behave this way. A major advantage of having images in an RGB working
space is that we can work numerically for gray balancing. Setting any
pixels we wish to be neutral is as easy as using one of the Photoshop set
neutral eye-dropper tools to ensure that R, G, and B are identical values.
RGB working spaces are good archive spaces. That is, saving a document
in one of these RGB working spaces allows us to use ICC profiles to
convert these images to as many RGB, CMYK, and even Grayscale color
spaces as many times as we wish to output the document.
A user can open and edit a document in an RGB color space that isn't
based upon the behavior of a well-behaved RGB working space if they
so desire. I can open a document created from a scanner or digital camera
and edit that data. As long as there is an embedded profile associated with
