[argyllcms] Re: Display measuring at maximum brightness beneficial?
- From: edmund ronald <edmundronald@xxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 22 Jun 2011 14:19:27 +0200
I think white LED backlight displays are basically switched -on/off- with
the duty cycle determining the brightness.
Has anyone looked at spectral drift here? There may be thermal effects
involved.
On Wed, Jun 22, 2011 at 2:11 PM, Nikolay Pokhilchenko <nikolay_po@xxxxxxx>wrote:
> 22.06.2011, 15:57 Edmund Ronald wrote:
>
>
> http://photofeedback.blogspot.com/2011/05/calibrating-macbook-pro-display.html
>
>
> Yes. But Juergen Lilienthere have proposed the spectrum correction for
> this case. The spectrum correction of white points may be useful, because
> the spectrum of light sources can changing significantly with brightness
> changing. For example, while dimming the CCFL.
> Please, excuse me for my English.
>
>
> On Wed, Jun 22, 2011 at 1:46 PM, Nikolay Pokhilchenko
> <nikolay_po@xxxxxxx<http://sentmsg?compose&To=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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