Re: Gamma values on Windows XP
Re: Gamma values on Windows XP
- Subject: Re: Gamma values on Windows XP
- From: "Bruce J. Lindbloom" <email@hidden>
- Date: Wed, 12 Feb 2003 10:33:51 -0600
Chris Murphy wrote:
>
First and foremost, it's not going to make that big of a difference
>
because regardless of what gamma you calibrate your display to,
>
Photoshop will use display compensation to compensate for the actual
>
tone reproduction of your display.
(snip)
>
In theory, changing the display as little as is necessary to calibrate
>
it will provide a better performing display. Maybe if we had 10-bit
>
DACs in display cards this would be less of an issue, but I've seen
>
calibration induced posterization using gamma 1.8. Therefore, I just
>
don't take the chance, even if it were calculated at being a small risk.
I agree completely. From an archival or working space point of view, I
believe 2.2 is a very good choice, since it is better able to represent a
perceptual grayscale with minimum quantization (posterization). See
<
http://www.brucelindbloom.com/CompandCalcHelp.html#BestGammaForLab> for
details.
Furthermore, coercing your monitor's apparent gamma by loading a curve into
the VLUT reduces the number of unique levels driving the display (at least
until we have 10-bit DACs fed by VLUTs that convert 8-bit data into 10-bit
data as Chris pointed out). Reducing the number of unique levels increases
the possibility of visible quantization. So a curved VLUT gains nothing and
loses levels -- a pretty bad trade-off, IMO. I've always been an advocate of
loading your VLUT with a ramp (to keep the number of unique levels per
channel maximized at 256) and then relying on Photoshop to compensate for
differences between the working space and the monitor.
<SOAPBOX>
1) Capture scanner and digital camera data in high-bit, from profiled
devices.
2) Assign *and convert* captured data to the RGB working space for archiving
and editing. Use 8-bit or 16-bit working space depth according to your
comfort level. I think that 8-bit is sufficient for most situations,
provided the working space is intelligently chosen.
3) Use a working space whose gamma is 2.2 and whose size and shape are
adequate to contain the colors that are important to you (and your
customer). Use the smallest, tightest fitting working space that meets these
criteria.
4) Always load your VLUTs with ramps and keep them there.
5) Profile your monitor (while the VLUTs are already ramped and will remain
forever ramped) and let Photoshop color manage the display for you.
6) Down with 'vcgt'! <g> (Except when using it to force ramps into the
VLUTs.)
</SOAPBOX>
--
Bruce J. Lindbloom
email@hidden
http://www.brucelindbloom.com
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