In some situation there is no access to a displays VideoLUT
hardware, and this hardware is what is usually used to implement
display calibration. This could be because the display is being
accessed via a web server, or because the driver or windowing
system doesn't support VideoLUT access.
There are two basic options in this situation:
1) Don't attempt to calibrate, just profile the display.
2) Calibrate, but incorporate the calibration in some other
way in the workflow.
The first case requires nothing special - just skip calibration (see the previous section Profiling in several steps: Creating display test values).
In the second case, there are three choices:
2a) Use dispcal to create a calibration and a quick profile
that incorporates the calibration into the profile.
2b) Use dispcal to create the calibration, then dispread and
colprof to create a profile, and then incorporate the calibration
into the profile using applycal.
2c) Use dispcal to create the calibration, then dispread and
colprof to create a profile, and then apply the calibration after
the profile in a cctiff workflow.
The first case requires nothing special, use dispcal in a normal
fashioned with the -o
option to generate a quick profile.The profile created will not contain a 'vcgt'
tag, but instead will have the calibration curves incorporated
into the profile itself. If calibration parameters are chosen that
change the displays white point or brightness, then this will
result in a slightly unusual profile that has a white point that
does not correspond with device R=G=B=1.0. Some systems may not
cope properly with this type of profile, and a general shift in
white point through such a profile can create an odd looking
display if it is applied to images but not to other elements on
the display say as GUI decoration elements or other application
windows.
In the second case, the calibration file created using dispcal
should be provided to dispread using the -K flag:
dispread -v -K TargetA.cal DisplayA
Create the profile as
usual using colprof. but note that colprof will ignore the
calibration, and that no 'vcgt' tag will be added to the profile.
You can then use applycal to combine
the calibration into the profile. Note that the resulting profile
will be slightly unusual, since the profile is not made completely
consistent with the effects of the calibration, and the device
R=G=B=1.0 probably not longer corresponds with the PCS white or
the white point.