Re: Repetitive Calibration with Optical
Re: Repetitive Calibration with Optical
- Subject: Re: Repetitive Calibration with Optical
- From: Dana Gregory <email@hidden>
- Date: Wed, 22 Jan 2003 13:30:13 -0500
This reply is in two messages. This is #2 of 2.
Further Questions
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>
1. I always start PreCAL as an independent application. I have never
>
opened PreCAL under OptiCAL. It this a mistake? How can this make a
>
difference?
As mentioned above, it does not matter if PreCAL is launched directly, as an
independent application, or launched from OptiCAL. It does not make any
difference in how PreCAL functions. Additionally, the setting of the
'calibration enabled' checkbox in OptiCAL has NO effect on PreCAL.
>
2. What is the consensus on the "calibration enabled" check box in
>
OptiCAL? To leave it checked or not checked before hitting the
>
"Calibrate" button?
It does not matter whether the 'calibration enabled' checkbox is marked or
not when performing a calibration. OptiCAL will first remove any existing
calibration from the video card LUT so that it can measure the un-calibrated
state of the monitor. After OptiCAL calculates the calibration and downloads
the correction curve to the video card LUT it will then mark the
'calibration enabled' checkbox regardless of its condition prior to running
the calibration process.
>
3. How do I reset the LUT in Windows? It was suggested to uncheck the
>
"calibration enabled" check box in OptiCAL. To test OptiCAL, I need a
>
way to do this outside of OptiCAL.
When the 'calibration enabled' checkbox is unmarked in OptiCAL a 'linear' or
'1:1' LUT is downloaded to the LUT on the video card. OptiCAL uses a
standard Windows system call to download the LUT. If OptiCAL is unable to
correctly reset the LUT then it is unlikely that any other application could
either. You can check out PowerStrip at <
http://www.entechtaiwan.com> which
is a utility that can set the video card LUT among other things.
>
4. C. David Tobie brought up a very interesting issued regarding the
>
whitepoint setting in OptiCAL. I have been setting the whitepoint to
>
D65 in PreCAL and D65 in OptiCAL. Is this double defining the
>
whitepoint?
No, this is not about 'double-defining' the Whitepoint. This is about PreCAL
knowing nothing about the settings in OptiCAL. You want to calibrate your
monitor to D65. You have to tell both PreCAL and OptiCAL. So you launch
PreCAL, tell it you want to calibrate to D65 and then proceed to adjust the
RGB Gain controls of the un-calibrated monitor so that when you are done the
un-calibrated monitor has a Color Temperature of D65! You've actually
calibrated the Color Temperature in the hardware itself.
If you then tell OptiCAL to also calibrate to D65 OptiCAL will calculate the
difference between the D65 Target Color Temperature you have requested and
what it measures the un-calibrated monitor to currently be. Of course the
monitor is already D65 because you just calibrated it in PreCAL. So OptiCAL
will calculate that no Color Temperature correction is needed in the LUT.
You can tell OptiCAL to not even bother to think about adjusting the Color
Temperature by setting 'Native' as the Target Whitepoint because you know
that the Native Whitepoint of the monitor is already D65.
>
5. Standard or Precision mode, which one?
The difference between Standard and Precision has to do with setting the
Black and White Luminance values of the monitor and nothing else. If you are
using PreCAL then you have already set your White Luminance using the RGB
Gain controls so the only difference is how you set the Black Luminance in
OptiCAL. In Standard mode you set the Black Luminance by observing a visual
target while you adjust the Brightness control. In Precision mode you set
the Black Luminance by observing a numeric value that is measured using the
colorimeter and adjusting the Brightness control until that measured value
matches your Black Luminance target value.
There is no one answer to this question. Some like the visual target and
some like the numbers.
Even if you are going to use Precision mode you have to decide what Black
and White Luminance target values you want to use and running a Standard
calibration is the way to find out. So at least your first calibration is
going to be in Standard mode.
If you then want to use Precision mode, create a Target File by selecting
"Save Target As" from the File menu, include Luminance values in the target
file when prompted. This will include the Black and White Luminance values
that were measured after you set your Brightness and Contrast controls in
Standard Mode. Then use that Target File when you calibrate in Precision
mode so you will have the right Target Luminance values for your monitor.
The 'default' values (e.g. 0.30/80.0) are just defaults, not Golden Values
that hold for every monitor.
The main reason for Precision mode is if you are calibrating multiple
monitors that will be viewed side-by-side. In such a situation it is
necessary to closely match the Black and White Luminance values of all the
monitors.
--
Dana Gregory 609 895-7454
ColorVision Inc. Engineering Director
5 Princess Road email@hidden
Lawrenceville, NJ 08648
http://www.colorvision.com
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