[argyllcms] Re: Contrast vs Brightness on my LCD monitor and related questions

  • From: "Hal V. Engel" <hvengel@xxxxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx
  • Date: Sat, 6 Dec 2008 15:46:19 -0800

On Saturday 06 December 2008 14:55:20 Graeme Gill wrote:
> Peter Karp wrote:
> > Are you aware of programs which measure gamma different then as
> > simplified gamma function? I think that none of the usual solutions to
> > calibrate a monitor will use a GOG or further model.
> As I understand it, there is certainly software out there that
> will do various least squares fits to get a gamma number
> (Gernot Hoffmann for one, if my memory is correct).

LCMS has a  function that will give an estimated gamma from a set of values in 
a gamma table.  I have not tried this but from a series of measurements it 
should be possible to put the scaled L* values of those measurements into a 
gamma table and use the cmsEstimateGammaEx() function to get a good estimate 
of the actual gamma of a device.  This might not give better results for 
devices that are well behaved (like most CRTs) but might do better for devices 
that are not as well behaved (like some LCDs).  I have not looked at the code 
in this function to see what algorithm it uses.

> The gamma measure used in the Argyll utilities is a simple
> 50% measure ("what pure gamma/exponent value will give the same response
> relative to white at 50% input, as the actual response curve").
> This measure is fast to measure, simple to compute, independent of
> the black point treatment and exact curve shape, and corresponds well
> to the overall look of the response curve.
> Graeme Gill.

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