Does it make a difference
Does it make a difference
- Subject: Does it make a difference
- From: "Mark Rice" <email@hidden>
- Date: Tue, 25 Oct 2005 22:50:16 -0400
Yes, it makes a big difference. Because gamma is a logarithmic?? (I am not
sure if it is logarithmic or some other function), a number of values tend
to bunch at the top or bottom of the scale. Since I referred to the LVT film
recorder, I will use transparencies as the medium for an example. With a
normal gamma function, and a 26 step gray scale that the LVT used for
calibration (this is burned in my head, as we had four LVT's and a Lightjet
that I calibrated 5 times per day!!) the darkest 5 steps of the gray scale
appeared as solid black, even though a densitometer could detect subtle
differences between them. Using the "equal brightness scale", or L*, the
step above solid black appeared to be visibly lighter than the blackest. The
3rd step appeared visibly lighter than that, and so on. At the lightest part
of the scale, the 25th step appeared visibly darker that the 26th step.
That is the point of using the L* scale - to imitate the gradation steps in
a real image, so that one can visibly detect what is happening.
Mark Rice
-----Original Message-----
From: Roger Breton [mailto:email@hidden]
Sent: Tuesday, October 25, 2005 7:51 PM
To: Mark Rice; ColorSync
Subject: Re: L* scale
> Gamma is a poor measure as it is skewed toward one end of the scale.
> L* is much more valuable for achieving a good look, but does not have
> a gamma equivalent.
>
> Mark Rice
Please excuse my ignorance, Mark, but does it really make a (perceptible)
difference? Whether the original RGB Luminance is converted to Y through a
power function as gamma (even if it does not perfectly fit the measured
data) or obtain through some *other* function? In the end, I think they all
come down to either XYZ or Lab, and then disseminated through the other
device profile. I guess I ought to revisit L* on my next re-calibration
outing.
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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| >Re: L* scale (From: Roger Breton <email@hidden>) |