[argyllcms] Re: What does dispcal actually do?
- From: Ben Goren <ben@xxxxxxxxxxxxxxxx>
- To: argyllcms@xxxxxxxxxxxxx
- Date: Wed, 28 Nov 2012 12:30:22 -0700
On 2012-11-28, at 12:13 PM, Nikolay Pokhilchenko wrote:
> There is two aims of calibration: correct brigtness response and neutrality
> along the neutral scale R=G=B.
Another way to put it is that, before calibration, RGB values simply equate to
whatever voltage responses the hardware happens to have. After calibration (by
whatever means -- vgct matrices or voltage knobs or whatever), a gray ramp
displayed on the monitor will be a neutral gray with the chosen chromaticity
and gamma. Single-channel ramps will have a comparable luminance (but,
obviously, not chroma) response.
Profiling provides a mechanism whereby known absolute colors (commonly
expressed in Lab or XYZ space) can be translated to corresponding RGB values
for that display using that calibration. The profile associated with an image
(sRGB, Adobe RGB, etc.) maps the RGB values in the image to an absolute color
space, so the combination of the two profiles provides a way for absolute
colors to be recorded and displayed.
As with anything analog, the physical response of the display drifts over time.
To compensate for this, a new calibration can be created with the same
parameters as before, after which the original profile generated earlier will
again properly characterize the display's behavior. Sometimes the drifting is
enough that calibration improves the response but it's still not a good enough
fit to the original response; at that point, a fresh profile needs to be
created as well.
Cheers,
b&
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