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Re: "native" gamma (was: fundamental question - monitor profile as working RGB?)
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Re: "native" gamma (was: fundamental question - monitor profile as working RGB?)


  • Subject: Re: "native" gamma (was: fundamental question - monitor profile as working RGB?)
  • From: bruce fraser <email@hidden>
  • Date: Wed, 10 Dec 2003 08:19:54 -0800

At 8:22 AM -0600 12/10/03, email@hidden wrote:

The thread of this topic has lead me to another question...related to the
Barco Calibrator monitors. Is "Uncorrected Gamma" the same as native?
There are two choices in the Barco utility..."uncorrected" and "linear". I
am assuming (perhaps erroneously) that a linear gamma would be a gamma of
1.0 and that "native" and "uncorrected" are the same thing.

Can't help on that one-it's been a long time since I used a Barco-but it would seem reasonable to believe that "uncorrected" meant just that.

I'd like to hear more about why a native gamma would be theoretically
"better" then a gamma of 2.2 (or whatever your preference is). As a
devil's advocate kind of question, why not use the native whitepoint as
well?

Tweaking the gamma is always done in the video card's LUT, and since video card vendors generally care more about how many shaded polygons they can draw per nanosecond than they do about good color, those LUTs are 8 bit. So tweaking the gamma is exactly like drawing an 8-bit gradient in Photoshop, then editing it with Levels. You may start with 256 shades, but you'll end up with less. The bigger the adjustment (i.e., the further you go from the monitor's native behavior), the fewer levels you wind up with, and the more likely you'll encounter visible posterization in gradients.

On a CRT you can adjust the white point by making analog adjustments to the RGB gains, so there's no loss in digital counts, though you'll lose luminance at lower color temperatures. On LCDs, I (and many other) advocate using the native white point as well as the native gamma. (Basically all there is to adjust on most current LCDs is the strength of the backlight, though there are exceptions.)

Bruce
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