Graphics Programs Reference
In-Depth Information
different. This may produce an issue some users would want to avoid.
We will look at choosing and using a CMM in more detail and inside of
Photoshop in Chapter 2.
Assigning/Embedding
ICC profiles can be assigned to individual images and saved within those
images. This is sometimes known as
embedding
(or
tagging
) an ICC profile.
Assigning is a term used in Adobe applications to describe the tagging or
embedding of an ICC profile to an image. When saved, this embedded
profile is saved within the actual image data. This allows any ICC-aware
application to correctly reproduce the color in the file. Embedding a
profile does not alter the image data in the file. A file that has no embed-
ded profile is often referred to as
untagged
, or as my colleague Bruce Fraser
likes to call them, “mystery meat,” because the numbers have no colori-
metric meaning.
An analogy I like to use for untagged is as follows. I hand a photog-
rapher a box in which a single sheet of exposed 4 ¥ 5 film (with no iden-
tifying notches) resides. My objective is to have the lab properly process
this one sheet of film. The lab is at a tremendous disadvantage since they
have no idea what kind of film it is, whether it is positive or negative,
what ISO the film is, or how it was exposed. The likelihood the lab will
correctly process the film is infinitesimal. Now all I do is whip out a pen
and write on the box “Fuji Velvia, ASA 100, push
1
/
3
of a stop.” I have,
in essence, “embedded” a profile. At this point, the lab knows that film
is a transparency that needs E6 processing at plus
1
/
3
of a stop. The label
I made with the pen (the embedded profile) didn't alter the contents of
the box or the film one bit! Nevertheless, it did provide the necessary
information to extract the proper color. This is analogous to how embed-
ded profiles give meaning to the image data within a file. Although the
embedded ICC profile increases the file size, it doesn't alter the numbers
of the file at all. As we will see when dealing with Photoshop and other
ICC aware applications, files that have no embedded profile are quite dif-
ficult to deal with.
Anatomy of an ICC Profile
Many chapters could be written about the viscera of an ICC profile; I'll
try to distill the details. It is useful to know a little about how ICC
profiles differ.
There are several kinds of ICC profiles. We can say there are classes
of profiles such as
input profiles
, which are used for describing how an
input device, like a scanner or digital camera, sees color.
Display profiles
describe how a display reproduces color, and
output profiles
describe how
printers and other output devices render color. Some of these profiles are
more complex internally than others. Some profiles operate in only one
