[argyllcms] Re: Dispcal, esp. gamma, advice?
- From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 11 Jun 2008 20:09:14 -0700
On 2008 Jun 11, at 7:19 PM, Graeme Gill wrote:
Ben Goren wrote:
So, first -- I now have a SoLux task lamp with a ``5000 K'' bulb
that actually measures to 4700 K (but only when I remove the
diffuser...that reduces it to 4200 K).
They are rated as being 4700K. Apparently if you increase the voltage
you can get 5000K, but the lamp life will be noticeably reduced
(the lifetime is roughly proportional to the inverse 12th power of
the voltage, so the effect can be dramatic).
The lamp ships with a 4700K bulb, but I ordered it with a 5000K spare,
which spotread says is 4700K. The ``4700K'' bulb itself is a few
hundred K less....
When I get a chance, I'll play around with over-driving it, but I
think what I've got is ``good enough'' for now.
Now, I'm wondering: just what parameters, exactly, should I use
with dispcal, and why?
See <http://www.argyllcms.com/doc8/monitorcontrols.html>.
Ah -- thanks!
And does it even make any difference with a color-aware
application like Photoshop? Would that mean I should target the
native gamma to avoid loss of resolution?
No. Yes. The gamma basically affects only two things:
Non-color managed applications.
How well controlled the display is, which affects how
well the display profile can work.
That's what I suspected; I'm glad to have it confirmed.
I've seen lots of opinions and recommendations everywhere, all
over the map. ``1.8 for print; no, 1.8 is outdated -- use 2.2;
etc.'' I'd appreciate some help getting un-confused....
If you're going to be using a color managed application, choose
something
similar to the native display gamma. You can tell this is close by
checking
that there is no dramatic shift in mid tone contrast when switching
between
un-calibrated and calibrated. Typically most displays are setup to
emulate
a traditional CRT, which has a native gamma of about 2.4. By
encoding images
with a gamma of 2.2, a dim viewing environment contrast enhancement is
achieved when such images appear on a display with a gamma of 2.4.
On this iMac, dispcal -R reports:
Uncalibrated response:
Black level = 0.50 cd/m^2
White level = 328.48 cd/m^2
Aprox. gamma = 2.14
Contrast ratio = 661:1
White chromaticity coordinates 0.3210, 0.3325
White Correlated Color Temperature = 6054K, DE to locus = 1.4
White Correlated Daylight Temperature = 6056K, DE to locus = 3.5
White Visual Color Temperature = 6013K, DE to locus = 1.4
White Visual Daylight Temperature = 6164K, DE to locus = 3.3
(Curious how much that's changed from here: //www.freelists.org/archives/argyllcms/09-2007/msg00093.html
)
I'll use 4700K for color matching; native white point for general
work; and native brightness (I can move the SoLux to match) and a
gamma of 2.14 for both. Sound rational?
Cheers,
b&
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