Re: laptop calibartion
Re: laptop calibartion
- Subject: Re: laptop calibartion
- From: Roger Breton <email@hidden>
- Date: Tue, 29 Apr 2008 21:50:45 -0400
Hi David,
About that tip, I'm not 100% clear on it.
He writes:
> Run the calibration once normally, adjusting the screen's backlight control
> (the Brightness slider in the Displays system preference) to reach the desired
> white luminance (120cd/m2 in our case).
>
> Then, record the position of the Brightness slider. About the easiest way to
> do that is to take a screenshot. Command-Shift-3 will grab a picture of the
> entire screen, while the more-useful Command-Shift-4 will enable you to select
> what you want captured.
So, first step it to adjust Brightness to a 'desired' level, like 120cdm/2.
Record the position of the Brightness setting, then, somehow (screen grab,
whathever).
> Move the Brightness slider all the way to the right to full brightness, then
> run the calibration from start to finish with the same parameters (ie 6000K,
> 2.2 and 120cd/m2), but this time skip the step where you adjust the backlight.
> In other words, run the entire calibration with screen brightness at maximum.
So, using max Brightness, let the software tune the LUT in the video card to
a gamma of 2.2 and desired luminance. Presumably, the application will
reduce each max RGB channels to bring the calibrated luminance down, to 120
cd/m2.
> Once you've completed the calibration and saved a profile to your system, set
> the Brightness slider in Displays back to the position you noted in step 2.
In other words, here, cheat the calibration.
> Keep the screenshot, since you may accidentally (or intentionally) adjust the
> screen brightness later, then need to set it back to the optimum position.
Scaling the brightness this way, after the fact, actually "eliminated the
main gripes with both the second-generation 15-inch and 17-inch MacBook
Pros", the author writes.
Well, in general, altering the Brightness of the backlit this way will
directly impact Y, the Luminance, but, in principle, in an "ideal world",
that should not affect or have minimal impact on x and y, the
chromaticities.
I recently did this something similar for a client, after having calibrated
someone's LCD screen, who didn't really have a huge need for color accuracy
after all. All the persone was concerned with was the fact that I had
lowered the luminance down. So, I reasoned, in this case, I saved myself the
trouble of re-calibrating ; all I did was to raise luminance a few
candeleas, enough to please the person as, in principle, that wouldn't
affect the chromaticities too much (it did, but that's beside the point).
But in the case of the older MacBook Pros cited above, the cheat described
is akin to stretching the LUT onto a wider Luminance range, all of a sudden.
I fail to see how that solves the color quirks described by the author.
Maybe I should re-read the article better...
Roger Breton
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