Re: Luminance nomenclature, STILL wanting to see constant L*
Re: Luminance nomenclature, STILL wanting to see constant L*
- Subject: Re: Luminance nomenclature, STILL wanting to see constant L*
- From: John <email@hidden>
- Date: Sun, 5 Nov 2006 10:34:49 -0800
Unfortunately, Ken took that quote out of context. In the original
post, I quoted Maureen Stone (Field Guide to Digital Color), saying:
"In many graphics texts and tutorials, an equation derived from the
NTSC definition of luma (the Y of IYQ), is routinely recommended to
compute luminance for any arbitrary RGB triples. This is wrong. Not
only is this based on an obsolete set of phosphors, it confuses the
non-linear luma with luminance. (See chapter 6)."
Roger gives the correct integrated definition of Luminance. The CIE
gives the functional/working definition of Luminance with the
Luminosity Function. The CIE defined the Luminosity Function in order
to relate perceived brightness to radiated energy. They defined the
tristimulus value Y (of XYZ) to match the Luminosity Function. The
"L*" of CIELAB is another representation of Luminance, and is the one
probably most relevant to this list.
Hope that clears things up. See you at the Color Imaging Conference!
John
On Nov 4, 2006, at 2:18 AM, Roger Breton wrote:
"Luminance" apparently means different things in different contexts.
Just because people use the term incorrectly in different contexts
does not
make those uses correct. (Dare I mention the term "metamerism"?)
Luminance
has a specific meaning whether or not people understand it and
apply it
correctly.
Ken Fleisher
Luminance is defined by the CIE. So it can only mean one and only
one thing
to everybody. I believe it is the integration of the area under the
curve
for the visibility function, V-lambda. It is reported in candelas per
squatre meter.
Roger Breton | Laval, Canada | email@hidden
http://pages.infinit.net/graxx
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