Camera/Scanner Profile
Parameters Dialog Help Window
LProf is an open source application that creates
ICC profile
for cameras, scanners and monitors.
Resolution (CLUT points)
This set of radio buttons are used to select how
many
points will be included in the profiles Color Look Up Table
(CLUT). Select smaller values to make small but less accurate
profiles. Select larger values to create larger more accurate
profiles. This can also be used to make
Matrix/Shaper profiles by selecting the Matrix radio button.
Matrix/Shaper profiles will be the smallest of all profile
types.
Profile Verbosity
These radio button allow you to control how much
additional information is stored in the profile. Selecting
"Only
required tags" will store only information that is absolutely needed in
the profile. This makes for smaller profiles.
"Store
additional tags" stores additional information but does not store
measurement information. "Verbose, store anything" will
include
everything that can be included in the profile including measurement
information that is useful to the Profile
Checker and other software such as iccexamin.
Regression Parameters
This section now features
an automatic
smoothness feature. With "Auto optimize smoothness" selected
the
profile generation code will use Randomized General Cross Validation
(RGCV) to try different smoothing factors, and to determine (and
eventually use) the "best" one, with the lowest RGCV estimate.
Best in this case means the smoothness factor results in the
lowest delta E. This is
based on:
Wahba, G., Johnson, D. R., Gao, F. and Gong, J. "Adaptive
tuning of numerical weather prediction models: Part I: randomized GCV
and related methods in three and four dimensional data assimilation."
TR 920, April 1994.
A short version is located here:
Monthly Weather Review, 123 (1995), 3358-3369, under the
title "Adaptive
Tuning of Numerical Weather Prediction Models: Randomized GCV in
Three-and Four-Dimensional Data Assimilation."
Automatic smoothness optimization can be influenced by setting
different values in the spin box to the left of the Auto optimize
smoothness radio button. Setting positive values in the spin
box
will result in smoother CLUT curves than the automatically estimated
smoothness value and setting this to negative values will result in
CLUT curves that fit the data points more closely at the expense of
reduced CLUT curve smoothness. In most cases the default
value of
zero (0) should
yield optimal
results and is
a good starting
point. In some cases users have reported that the smoothness
factor that yields the lowest delta E does not give the best actual
results. Usually this shows up a color reversals in very dark
and/or highly saturated parts of images. This has been
specifically observed when profiling Nikon film scanners with very
highly saturated/dark greens. The solution is to increase
value
in the "Auto optimize smoothness" spin box or to set a "Manual
smoothness" value that is higher than the automatically selected value.
There are 13 smoothness factor values that can be selected by
either the "Auto optimize smoothness" feature or manually.
Users can also set the smoothing factor manually by selecting the
Manual smoothness radio button. This has the advantage of
running faster during profile creation but users will be on
their
own for selecting the best smoothness setting. Values between
-6
and 6 are valid with higher values resulting in increased smoothness.
Values near zero (0) are a good starting place.
White Point Handling
Starting with version 1.11.5 LProf now features a new set of
controls for setting the profiler white point handling. These
features are very powerful and should allow users to select the correct
white point handling for each device. The white point
location
can be set in six different ways using the radio buttons in the
"Location" button group. For most uses the "Dmin target
patch"
and "Adapt device white point" are the right choices. "Adapt
device white point" is how LProf has done this in the past.
On the right side of the Location button group are the RGB,
L*a*b* and XYZ buttons. Selecting these will allow you to
specify
a specific white point. The XYZ and L*a*b* buttons
will
allow you to specify the white point as an absolute value in either the
CIE-Lab or CIE-XYZ color spaces. The RGB setting will set the
white point to a user specified RGB color in the target image.
You can also use the "Pick from image" button to select an
area
in the target image that will be used for setting the white point. The
radio buttons in the "Luminance Scaling" button group are for setting
how the profile will handle RGB values in images that are higher than
the RGB values for the calculated white point.
Chromatic adaption &
viewing condition
This functionality has been completely revamped
with the
release of LProf version 1.11.5 and is now much more powerful.
It
is now possible to set both the "Assumed viewing conditions for the
captured medium" and the "Assumed PCS viewing
conditions".
The "Assumed
viewing conditions for the captured medium"
are the lighting that were in use at the time the profiling target was
captured. For most situations this should be set the the
default
value of "Original scene - Bright Outdoors". There are other
pre-defined setting that are based on published standards that can be
selected. In addition, users can set these to almost any
arbitrary set of values. Settings other than "Original
scene - Bright Outdoors" are in general very specialized and should
only be used by users who know specifically why they are making this
change.
In most cases the "Assumed
PCS viewing conditions" should be set to
"ISO-364 P2 ICC reference medium". Like "Assumed
viewing conditions for the captured medium" setting there are a number
of industry standard presets available and users can select almost any
set of arbitrary values. Settings
other than "ISO-364 P2 ICC reference
medium"
are in general very specialized and should only be used by users who
know specifically why they are making this change.
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1998-2007
LProf.
All Rights Reserved.