[argyllcms] Re: Display measuring at maximum brightness beneficial?
- From: edmund ronald <edmundronald@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 22 Jun 2011 13:57:20 +0200
http://photofeedback.blogspot.com/2011/05/calibrating-macbook-pro-display.html
On Wed, Jun 22, 2011 at 1:46 PM, Nikolay Pokhilchenko <nikolay_po@xxxxxxx>wrote:
> 22.06.2011, 14:50 от Juergen Lilien wrote:
>
> Many instruments especially spectrometers seem to have accuracy problems
> when measuring at low light levels. Couldn't it be beneficial, if we
> would first measure a display at its maximum brightness setting,
> subsequently set the brightness to the desired level, remeasure at least
> the new white point spectrum (I suppose the white point of the backlight
> unit will change when dimmed) and then try to compensate/recalculate the
> first measured data based on the new WP/brightness?
>
>
> I think it's a good idea, nor dumb.
> If one have spectrum data, he can just multiply this data by spectrum
> difference between white points, calculated after brightness changing. But
> in case of spectrum distribution change, this methode will work only for
> profiling, not for calibration.
>
>
> Could this strategy be beneficial at least for measuring the very low
> gray/brightness levels?
>
> I suppose it could.
>
> Graeme, it's a good idea. We can implement the modes of calibration and
> display reading at high brightness.
> I propose the next workflow which can be implemented in dispcal and
> dispread:
>
> 1. Calibrating desired white point and desired brightness.
> 2. Measuring and save desired white point spectrum.
> 3. Changing the hardware brightness of the display baclit to maximum. There
> is the check "Is the sensor of instrument saturated"? needed. If saturated,
> then operator should decrease brightness.
> 4. Measuring and save high brightness spectrum.
> 5. Calculating spectral "brightness correction coefficient" by devision the
> low brightness spectrum by high brightnes spectrums previously saved.
> 6. Doing the calibration or measurements with applying (multiplying by)
> the correction coefficient.
>
> That way the program can predict the spectrum of patch on screen at desired
> brightness, while the measurements have done at maximum brightness. I
> suppose this way can increase the tolerance of measurements and resulting
> calibration and profile.
> One reason for error I can see, is the display matrix transparency drift
> with temperature. At higher brightness the temperature of matrix will be
> higher. And if there is matrix temperature drift of color, there may be an
> error. But this error may be less than instrument error at low brightness.
>
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