spectro/dispcal
Summary
Given a calibration target [white point, maximum brightness, and
response curve ("gamma")], display a series of test patches on the
display, and using the colorimetric values read, create red, green and
blue lookup tables that make the display meet the desired target.
Usage
dispcal [-options] inoutfile
-v
Verbose mode
-d
Print debug diagnostics
-c comport Set COM port, 1..N
(default 1)
-a
Run instrument calibration
-i 92|SO Select
target
instrument (default DTP92)
92
=
DTP92, SO = Spectrolino
-q [lmhu] Quality
- Low, Medium (def), High, Ultra
-t temp
Set the target white point daylight color temperature in deg. K
-w x,y
Set the target white point as chromaticity coordinates
-b bright
Set the target brightness in cd/m^2
-g gamma Set the target
response curve gamma (Def. 2.2)
Use "-gl" for L*a*b* curve
Use "-gs" for sRGB curve
-V
Run verify pass on final curves
-n
[X11 only] Don't set override redirect on test window
inoutfile
Base name for input[.ti1]/output[.ti3] file.
Comments
This is the utility is used for calibrating a display, to reach
specified target behaviour.
The -v flag reports progress information, as
well as other statistics about the progress of calibration.
The -d flag causes serial communications
diagnostics to be printed to stdout. This can be useful in tracking
down why an instrument can't connect.
The instrument is assumed to communicate through a
serial
communication port, and the port can be selected with the -c
option,
if the instrument is not connected to the first port. If you invoke dispread so as to display the usage
information (i.e. "dispread -?" or "dispread --"), then the discovered
serial ports will be listed on Windows and Mac OSX systems.
By default dispcal expects to use an Xrite
DTP92
CRT instrument, but the GretagMacbeth Spectrolino can be selected by
using the
"SO" argument to the -i option, for use on either a CRT or LCD
type of display.
Quality - Low, Medium (def), High, Ultra. The -q flag determines how much time and
effort to go to in calibrating the display. The higher the quality, the
more test readings will be done, the more refinement passes will be
done, and the more detailed will be the calibration of the display.
Set the target white point, daylight color temperature in deg. Kelvin.
By default, the native white point of the display is used.
Typical
values might be 5000 for matching printed output, or 65000, which gives
a brighter, bluer look. The cooler white point may limit the maximum
brightness possible.
An alternative to specifying the white point in
degrees Kevin, is to specify it in chromaticity co-ordinates. This
allows the white point to be a color other than one on the blackbody
locus.
Set the target brightness of white in cd/m^2. If
this number cannot be reached, the brightest output possible is chosen.
Set the target response curve gamma. This is
normally an exponential curve (output = input ^gamma), and defaults to
2.2, a standard sort of value. Two alternatives to the power curve are
to use the sRGB curve response curve, which is an exponent curve with a
straight segment at the dark end (-gs),
or the L* curve, which is the response of the CIE L*a*b* perceptual
colorspace (-gl).
Run verify pass on the final curves. This
is an extra set of instrument readings, that are used to estimate how
well the device will match the targets with the computed calibration
curves.
The -a option
runs through the black and sensor
relative
calibration routines for the Xrite DTP92 instrument. If a Spectrolino
is being used, then a white calibration will always be performed before
the instrument can be placed on the display.
When running on a UNIX based system that used the X11
Windowing
System, dispread normally selects the override redirect so that
the
test window will appear above any other windows on the display. On some
systems
this can interfere with window manager operation, and the -n
option
turns this behaviour off.
The final parameter on the command line is the base
filename for the .ti1
input file, and the .ti3 output
file. dispread will add the .ti1 and .ti3 extensions
automatically.
If a large number of patches is being read, the screensaver or
powersaver on many
systems can interfere with the operation of dispread. It is therefore
advisable
in these cases to manually turn off the screensaver before commencing
the
measurements.
The calibration tables produced maintain the maximum level of precision
available on a system. If the system RAMDAC outputs are better than 8
bits per component, then the resulting curves can reflect this.
Note that currently there is no support for adjusting the display
controls (brightness, contrast, R, G & B channel controls etc.) and
providing feedback on how close the native response is to the targets.
Currently it is up to the user to adjust these controls using some
other feedback, before running dispcal.