[argyllcms] IRE

[Leonard Evens <len@xxxxxxxxxxxxxxxxxxxxx>]

Okay, some google searching revealed what IRE means.   I believe it goes
something like this.  If you normalize the voltage fed to the monitor as
a percentage of the range from the minimum (for pure black or blanking
the screen) to maximum needed to produce pure white (at the given
highest luminance that the monitor is set for), that percentage is
called the IRE level.  Then the relationship between the luminance of a
pixel on the screen and the IRE level needed to produce that luminance
is assume to be of the form.

Luminance = Maximum Luminance x (IRE level)^gamma

(Since IRE is a percentage, it should vary in the formula  from 0 to 1,
e.g., 30 percent means 0.3.)

Thus, if you measure the Luminance for different IRE levels, you can
calculate the exponent gamma.   Since the rule is only an approximation
and is not satisfied exactly,  you find you get different value of gamma
from different points on the graph.  The actual formula is

gamma = [log(Luminance) - log(Max)]/log(IRE)

If you use this formula in the chart at the link given previously
www.homecinemaengineering.com/pdfs/ISFExample1.PDF
you will find it gives the values of gamma in the bottom graph.

I don't know if this helps anyone else, but at least it cleared it up
for me.

-- 
Leonard Evens <len@xxxxxxxxxxxxxxxxxxxxx>
Mathematics Department, Northwestern University

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[argyllcms] IRE