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CS Gamma Measure in Extended zone (i.e. Between Legal and Peak)

 
Author ebr9999
ZRO
#1 | Posted: 2 Jul 2022 11:17 
I have been working on parametric EOTF as tool for compensating non linear response of my Oled display (see here if interested). For this reason I was interested to see the outcome of a 3DLUT generated after a parametric EOTF.
So I have generated and measured 2 3DLUTs based on a 33 points parametric gamma, generated after a Grey ramp large in extended range: the first one generating a pure 2.4 gamma (og=ig) and the second one targeting at point 24 and 32 a 2.2 gamma.

The 3DLUT generation is OK, (i.e increased L at those points) in , but what surprised me was the way EOTF is measured by CS in the area between legal and peak stimulus.
Looking at CS plotting (having as reference a 2.4 Rec709 EOTF), I see measurements above the reference EOTF, but EOTF gamma above 2.4

So, I have imported the two bcs' and computed gamma for both normalizing to legal level (and using the same formula also for levels above legal) and normalizing to peak level. You can see in the attached picture the relevant plotting on both measurements. What surprised me even more is that CS measures EOTF based on a Gamma formula with not normalized values. I cannot understand what kind of measurement it is, but obviously it is not a power gamma.

I understand the point, very correct, to measure EOTF on legal level, but above them I expect consistency, not a computation that has nothing to do with power gamma!

comparing.zip Attached file:
Excel and bcs

 
Gamma Plotting
Gamma Plotting

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 CS Gamma Measure in Extended zone (i.e. Between Legal and Peak)

 

 
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