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Gamma-corrected to IRE

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Chris Clementson
Gamma-corrected to IRE
on May 14, 2018 at 12:47:07 am

I have the following code for gamma correcting a reflectance value. For example, if the reflectance is 18% (0.18) and the gamma is 0.45, this gives me a value of 40.9. The 40.9 value agrees with everything I've read.

=(1.099*0.18^0.45-0.099)*100

The question is, what is the math to convert this to IRE units? I am expecting to see a value of 43.4 according to everything I've read.

If I change the reflectance to 90% as found on a typical test chart:

=(1.099*0.9^0.45-0.099)*100

I get a value of 94.9. I believe this is correct. After conversion to IRE units it should be 100.

What is the correct way to convert these gamma-corrected numbers based on reflectance to IRE units?

Thank you.


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