[argyllcms] Re: What does dispcal actually do?

  • From: Graeme Gill <graeme@xxxxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Thu, 29 Nov 2012 10:07:06 +1100

Richard Hughes wrote:
> Splitting up the screen "calibration" into two phases, calibration and
> characterisation is easy enough to explain. Characterisation can be
> explained as getting the accurate device response, but how do I
> explain calibration?

Hi Richard,
        no, I would say that Characterisation is measuring the device,
not setting a device response. I would call setting a device response
calibration. See <http://www.argyllcms.com/doc/calvschar.html>

> As far as I can understand it, dispcal does some kind of iterative
> algorithm to set the vcgt tables, with an optional target white point.

Yes. The white point can be chosen (which establishes the
end points of the RGB curves), and the iterative process
is to set curve shapes such that the R=G=B response has
consistent neutrality from white to black. (There can be a bend
near the black point though, to maximise contrast ratio).

> Could someone please explain in fairly technical language (assume the
> user knows about Lab and XYZ) what dispcal is actually doing?
> I've tried reading the source a bit for this but it's quite confusing.

Yes - it grew and grew, but I didn't feel like re factoring it into
several modules, which would be the correct course to reducing its

Do you need more detail than my above summary ?


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