So What Are the Sources of Variability?
First, in order to use color management we need to
characterize the proofing device. This involves printing
a reference target, measuring the color printed for
each patch, and then creating a color profile using this
data. The first two sources of variability are:
1. Uncertainty in the colorimetric measurement of
the printed reference target used to characterize
the proofer.
2. The modeling errors in the proofer profile
building process.
Now we are ready to make our proof. The proofer
profile we made is used in combination with the profile
that characterizes the reference printing condition
(which is based on the TR 001 reference data)
to modify the image content data so it will provide
the proper input to the proofer. We have added three
new sources of variability.
3. The modeling errors in the TR 001 profile
building process (we assume that the TR 001 data
have no variability).
4. The computational errors in the color management
system when it applies the profiles to
the data.
5. The variability of the proofer (changes in proofing
system performance between the time the characterization
data was printed and the proof is made).
Now that we have our proof, how close does the
target we printed along with the image data match
our reference data? To know that, we must measure
the target printed with the image data, which adds
another source of variability.
6. Uncertainty in the colorimetric measurement of
the target printed on the proofing device along with
the image data.
Do We Have to Account for Other Variability?
Part of the answer depends on whether we are comparing
the proof to the reference data or to a press
sheet that has been printed using a press that
matches the aim printing conditions (unrealistic, but
a simplification for this discussion).
If we are going to evaluate the match to a press
sheet, we account for the variability in the measurement
of the press sheet.
The Printed Sheet
The printing process itself has variability; and from a
systems point of view, we should assign a tolerance
to the variability of printing. For now, let’s leave that
out of the equation and assume that all we want to
do is see how well a particular printed sheet matches
the proof. Even in that scenario we need to add
another source of variability.