[argyllcms] IRE measurements

  • From: Niccolò Belli <darkbasic4@xxxxxxxxx>
  • To: argyllcms@xxxxxxxxxxxxx, janos666@xxxxxxxxxx
  • Date: Tue, 02 Nov 2010 16:03:57 +0100

Il 13/09/2010 01:14, János, Tóth F. ha scritto:
> yCMS uses the primary and white color coordinates for gamut conversion and
> IRE luminance values for gamma correction. But it also take care about the
> white balance. You can input three dimensional data for the IREs.
> It has some limits but you can work with 256 IREs.

From the yCMS Manual:

   Grayscale_Measurements format
   ire[1] measurement[1]
   ire[2] measurement[2]
   ire[n] measurement[n]

     "format"     = 0 -> CIE Y (all channels equal)
                    1 -> CIE Yxy
                    2 -> CIE XYZ
     "n"           = number of measurements   = [5..256]
     "ire"         = measurement at which IRE = [0..100]
     "measurement" = measurement value(s)     >= 0.0

     Be careful when using any measurements below 30 IRE.
     Some meters have lower accuracy at those levels, which might
     not give good results. If it happens, simply do not specify them,
     and yCMS will then assume that the display measures "correctly"
     below the lowest listed IRE.

Unfortunately HCFR does not support my spectrophotometer (Eye-One
Colormunki Photo) so I will have to use Argyll to do the measurements.

The -g parameter sets the number of patches in a set of combined
(nominally gray) wedges. This will typically be equal RGB or CMY values,
and by default will be equally spaced steps in device space.

If I understood correctly black equals to 0 IRE and white to 100 IRE
(but from wikipedia white seems to be 140 IRE). So I can use targen with
the -g parameter set to x while x is:

x - (x/100)*30 = 256 ==> x = 366

This gives me 256 useable measurements: 366 minus the measurements below
30 IRE [(366/100)*30=110]

Then I can find the corresponding IRE with:
IRE = measurement_number/3,66

Am I right? Is this what I need?


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