Quato iColor Display 3.7 User Manual page 10

8bit signal after 16bit correction (left) versus the 8bit signal
after corrections in 8bit (right).
D65
Tolerances for the whitepoint for paper type 1. The majority of
the probes is within the range of 5.600 to 6.000 K.
Without chromatic adaption, the display would render colors
much too cold (right). With adaption, the appearance (left)
looks like the original (top).
Comparison (from top to bottom) between L* , Gamma 2.2,
Gamma 1.8 and the TVI from ISOcoatedv2 shows that L* and
Gamma 1.8 match Offset printing quite well.
10
D50
losses in comparison to make all adjustments in an
8bit image and having a lot of losses later.
Calibration Basics
Apart from the calibration technology, the calibration
setup is also quite important. The right values for
Luminance, Gamma (or Gradation or Tonal response)
and Whitepoint are not always easy to find.
Whitepoint
Of course, according to ISO 3664 and others, D50
is the right whitepoint. But this does not match for
screens. A display, calibrated to D50, will always
looks to warm compared to a D50 viewing booth.
Research has found that for paper type 1 (gloss or
matte coated offset), a whitepoint between 5.600 K
to 6.000 K should be used to simulate the D50 ap-
pearance on a screen. Other paper types may need
different whitepoints - pretty much depending on the
paper color.
As the display no longer uses D50, we have to apply
a chromatic adaption to comply to the ICC-standard
of D50.In fact, iColor Display automatically uses a
chromatic adaption if a whitepoint other than D50
is used for the calibration. The default adaption is
„Bradford" as most image editing software makes
use of this adaption, too.
iColor Display offers some more adaptions like
vonKries, XYZ-scaling or Cat02/LMS. These adaption
should only be used if you need to comply to special
environments.
Gradation
The gradation or tonal response curce (TRC) is ano-
ther important part that needs to be adjusted cor-
rectly. Sometimes, one can find statements like „PC
uses Gamma 2.2 and Mac uses Gamma 1.8, and the-
refore the display has to calibrated to these values".
This is wrong because the gradation (gamma is one
possible gradation) is not defined by the computer
platform but by the working space that is used in
Photoshop and Co. Only if you do basic colorma-
nagement task on operating system level, the stan-
dard gradation of the operating system counts. Here,
Windows XP/Vista/7 and Mac OS X 10.6 make use of
Gamma 2.2 while Mac OS X 10.5 or older use 1.8.