Graphics Programs Reference
In-Depth Information
RGB (1998). This also illustrates how R0/G255/B0 alone can't tell us how
green this color is. There are hundreds if not thousands of different RGB
color spaces just as there are hundreds if not thousands of different
devices that create or reproduce RGB; same color model, different scale.
The same is true for many other color models such as CMYK, HSB,
Grayscale, and so on.
Device-Dependent Color Spaces
It is sometimes useful to think of color spaces based upon their origin. A
scanner or digital camera creates data in a color space specific to that
device. This is due to the fact that the actual filters used are different.
An Epson printer or a printing press each have a different color space
as well. This is due to the fact that the inks used to create the image
have different characteristics. All these color spaces are considered
device-dependent. The primaries in these color spaces are derived from
the colorants or filters of the device.
Other color spaces are synthetic or abstract and have no direct rela-
tionship to any specific device. The primaries of these color spaces were
chosen by their creators for other purposes. For example, there are color
spaces that were created for editing images. Within Photoshop these are
referred to as
working spaces
, a term created by Adobe.
The two most common color models we work with are RGB and
CMYK. Every capture device, be it a scanner or digital camera, produces
some unique flavor of RGB. Many printers accept RGB data for output
whereas others require CMYK data. Both RGB and CMYK are known as
device-dependent
color spaces. That means if we send the identical RGB
file, which are just numbers, to 10 different printers, we'll end up with
10 different color prints. The devices themselves all take the same
numbers and produce different colors, which is a significant problem.
Another way to look at this is that if we had 10 different printers and
wanted to produce identical colors on each, we would need 10 different
recipes (color spaces). As you can see, this makes life quite complicated.
Fortunately, color management allows us to create the correct color space
and values for each device.
The device-dependent nature of RGB and CMYK (as well as other
color models like Grayscale) is yet another reason why “working by the
numbers” can be so difficult. What is the correct RGB value to produce
a specific shade of red on an Epson 2200 running matte paper? What is
the correct RGB value to produce the same shade of red on a Fuji
Pictrography 4500 running gloss paper (if that's even possible)? There are
thousands upon thousands of RGB and CMYK color spaces, just as there
are thousands upon thousands of RGB input and output devices as well
as CMYK output devices. Each device produces and requires a different
and unique recipe of RGB, CMYK, or Grayscale. Keeping track of all these
color spaces and producing the right values of RGB or CMYK requires
Definition
Working space:
A color
space specifically
optimized for editing
images in a product like
Photoshop. Working space
like Adobe RGB 1998 and
so on are not based on
real-world devices but are
synthetic, mathematical
spaces that are ideal for
image editing. Working
spaces are discussed in
great detail in Chapter 2.
