Learn About Calibration Curves - Canon VarioPrint MICR i Series Operation Manual

Learn about calibration curves

Learn about calibration curves
What are calibration curves
The media family calibration procedure creates per media print mode two sets of C, M, Y and K
calibration curves: one for the front side and one for the back side.
During the media family calibration the printer uses the patch measurements of the calibration
charts to compensate the differences between the printed color values to the expected color
values.
How calibration curves are calculated
The illustrations below explain how the calibration curves are calculated.
1. When you use an i1 spectrophotometer to
measure a test chart with magenta gradients
from 0% to 100% the measured Lab values will
compose a straight line from paper white (Lab
0,0,0) to the maximum Lab color value at
100%.
Lab value
(0,0,0)
3. When you perform a media family calibra-
tion, all measured values of the patches are
compared to expected values. For every patch
and the in-between tone values a correction
value is calculated. In this example, patch 1
represents the 0% tone value and patch 5 the
100% tone value.
(0,0,0)
542 Chapter 15 - References
0%
∆E
ICC
Measurements
1 2 3 4
2. A Lab value is not easy for color compari-
sons. It helps to use the (∆E) metric to express
a color value.
The difference between the Lab value of a col‐
or and the Lab value of paper white (0,0,0) de-
livers such a ∆E value. This value is called: Dis‐
tance To White (DTW).
The maximum color value (expressed in ∆E)
refers to the 100% tone value. This value is
called: Maximum Distance To White (Max
DTW).
100%
4. Per color channel a smooth calibration curve
is composed that represents the correction val-
ues. These calibration curves are used to
slightly adjust the ink amounts the output pro-
file had defined: C=> C', M =>M', Y => Y' and K
=> K'.
In this example, the calibration results in print-
ing less magenta ink in the light areas and
more magenta ink in the darker areas.
5 Patch
∆E
(0,0,0)
0%
M'
0%
0%
Max
100%
M'
VarioPrint i-series MICR