Display Gamma
Display Gamma
- Subject: Display Gamma
- From: Steve Kale <email@hidden>
- Date: Sun, 14 Oct 2007 10:31:06 +0100
- Thread-topic: Display Gamma
Does anyone know how Gretag Macbeth¹s i1 Match software calculates the gamma
for a display? I understand there are numerous methodologies that can be
deployed depending on your theoretical preferences. For example, in a
recent discussion about the calculation of gamma for cinema display
calibration, a number of choices were discussed:
1) Display gamma
The gamma is compute in light to human eyes perception.
After approximation brightness (L) is expressed according to the signal (V)
using the equation:
L = V^gamma
2) Display Gamma with Black Compensation
In practice one can never achieve an absolute black and it is necessary to
take in account of the black you can really obtain.
This is usually done by computing Gamma after removing the "absolute" black
from every measure.
3) Camera Gamma (Standard Offset)
To have an accurate reproduction, some interpretations say that you must
apply a symmetrical treatment to the encoding one. The reference equation
being:
Y = ((V+offset)/(1+offset))^gamma
The "offset" is a parameter use at black encoding stage (and reproduction
using this method). It's value is 0.099 on all video standard. (0.055 in
sRGB)
4) Optimized (Regression)
This calculation method is based on the fact absolute black recorded by
camera is the absolute black projector can produce.
But offset in standard is roughly for 200:1 contrast ratio, a lot lower than
the current ratio a good display can achieve.
The optimized method tries to find the Offset AND Gamma parameters that best
match the measurements, black included.
I¹m intrigued as to how to relate the target gamma of my i1 Match profiled
computer display to my calibrated home theatre display.
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