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 13:30:12 -0500
This reply is in two messages. This is #1 of 2.
There has been a fair amount of discussion on this thread. Some of it
related to the subject line, some regarding questions about if and how
PreCAL and OptiCAL interact with each other, product improvement suggestions
and other issues.
Really, most of these questions and items have been addressed in previous
replies by David Tobie and others. At the risk of beating a dead horse, in
this message I will answer the original questions and address some of the
ancillary items.
This thread has combined information on how to use the tools as they exist
today and how the tools can be improved so that they would be easier to use
in the future. It is well known that having PreCAL as a separate application
is not an ideal solution. Even PhotoCAL is more graceful in handling this
issue! However, this message will discuss how to best use the tools as they
currently exist while we await future improvements :-)
The Original Question
---------------------
>
Does anyone know if repetitive calibration with OptiCAL creates a
>
situation where the monitor can no longer be calibrated properly. If I
>
use PreCAL and then calibrate and profile with OptiCAL, it drives the
>
brightness and contrast up on my monitor controls. Each time I run
>
PreCAL and then OptiCAL, it forces the monitor's brightness and contrast
>
settings higher and higher. After a few months of calibrating with
>
OptiCAL, I can no longer calibrate my monitor to the correct white and
>
black luminance points.
>
To solve the problem, I think that I need to reset my video LUT to get
>
my machine back to a clean starting point. Anyone know how to do this
>
in Windows 2000?
There is no cumulative effect of calibration with PreCAL and OptiCAL. When
PreCAL is launched it removes any correction curve that may have been
previously downloaded to the LUT in the video card. It does this by
downloading a 'linear' or '1:1' LUT to the video card to place the monitor
into an un-calibrated state so that we are only measuring and adjusting the
monitor hardware itself without any software calibration being involved. The
LUT in the video card is cleared in this manner regardless of whether PreCAL
is launched directly or from OptiCAL. The setting of the 'calibration
enabled' checkbox in OptiCAL has no effect on this. PreCAL will ALWAYS
remove any existing calibration from the video card LUT.
The setting of the RGB Gain controls can affect the White Luminance level as
well as the Color Temperature. For example, you may set your RGB Gain
controls to 74, 61, 58 and get a color temperature of 6500K and a White
Luminance of 85 candelas. You could then change the RGB Gain controls to 64,
51, 48 and still have a Color Temperature of 6500K but a White Luminance of
only 70 candelas. You might then increase your Contrast control to adjust
the White Luminance back up to 85. This might also cause you to need to
adjust your Black Luminance using the Brightness control. Needless to say,
there is interaction between the monitor controls: Brightness, Contrast and
RGB Gain. You could run yourself in circles.
The recommended procedure is: set the Contrast control to Maximum and leave
it there, set the Brightness control to your normal operating level, then
adjust the RGB Gain controls so that you get the correct Color Temperature
AND White Luminance.
--
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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