Talk:Relative luminance

message: Ok I think it really makes more sense to talk about *relative* luminance.  Color science both uses the concept of relative luminance (especially in the XYZ color space) and sometimes uses the concept of absolute luminance (at least I think so).  The concept of absolute luminance would come up in things like the transition between mesopic and scotopic and photopic vision.  
I don't know, the current page is a mess and makes little sense.
Suggested text:
Relative luminance follows the photometric definition of luminance, but with the values normalized to 1 or 100 with respect to a reference white.  Like the photometric definition, it is related to the luminous flux density in a particular direction, weighted by the luminosity function (Y) of the CIE Standard Observer.  The use of relative values is useful in systems where absolute reproduction is impractical.  For example, in prepress for print media, the absolute luminance of light reflecting off the print depends on the illumination and therefore absolute reproduction cannot be assured.
*plus add explanation of how we tend to see things in ratios, and not absolute values.  Possibly add disambiguation information from luma (video), plus formulas to calculate luminance for sRGB color space.  Add links to things like Lab color space.
Glennchan 05:12, 22 November 2006 (UTC)
replies: text: Glenn, it's a good thing you're up on this stuff.  I checked some books, and I'd say you're right that the "Y" that I was calling luminance is more often called relative luminance.  So that would be a good name for the article.  I'd be careful getting into not-so-accurate things like characterization of psychophysics via Fechner's law ("we tend to see things in ratios"); there's no need to introduce that here, or if you do then you have to talk about how it breaks down, and how Stevens's power law is a better description and is used to motivate L* etc.  I'll be away for a few days, so have at it.  Oh, and relative luminance values are often normalized from 0 to 1, as opposed to 100. Dicklyon 06:24, 22 November 2006 (UTC)
replies: text: I don't read that many color science books so I don't know if the term relative luminance is used more than luminance.  Although luminance would, more often than not, refer to relative luminance rather than the photometric or video signal uses of the word luminance.  I don't know how to rename articles, so I'll be lazy and leave that to someone else.  ;)  I'm not very familiar with Fechner's or Steven's power law; what I was getting at is that our vision is more ?interested? about relative values than absolute values.  Not talking about Fechner's or Steven's power law.Glennchan 06:00, 24 November 2006 (UTC)
replies: text: You can use the "move" button to rename a page; it's easy, and makes the old name a redirect.  You can consult lots of books at http://books.google.com.  And if you're not familiar with Fechner's law and how it breaks down, stay away from that perception topic, and it's very easy to say things that are not right. Dicklyon 20:02, 26 November 2006 (UTC)
replies: text: Ok, done.  In regards to normalizing to 100, this is done in Adobe Photoshop and what is cited in Poynton's glossary for his book.  I don't know what the practice is in the color science world, whether they use 100 or frown upon it.  In a practical sense, it doesn't really matter too much since the number you normalize luminance to is kind of arbitrary.Glennchan 22:13, 29 November 2006 (UTC)
thread_title:  Rename page and change scope to relative luminance? 

message: Regarding the reference of "RGB primaries" --> "display primaries" --> "primary chromaticities" 
Primary chromaticities is a better phrase to use since it describes a concept more exactly.  RGB primaries is sort of an ambiguous phrase, since primaries imply the primary colors red, green, and blue.  Granted, the word primaries alone may suffice.  
Some people who use the phrase "primary chromaticities" would be  and Poynton's textbook.  Glennchan 04:00, 2 December 2006 (UTC)
replies: text: Yes, that's what I usually call them, too.  It might be more clear to be more explicit and call them the red, green, and blue primary chromaticities.  Up to you. Dicklyon 04:12, 2 December 2006 (UTC)
thread_title:  Semantics - my bad