Talk:White point

message: :Re Merge - yes, good idea PAR 14:36, 9 December 2005 (UTC)
thread_title: Merging with Standard Illuminants

message: A white point and a standard illuminant are two completely different things and should not be confused!
A white point is exactly that: a point.  It is a set of (usually three) "tristimulus coordinates" (eg: CIE XYZ).  
If the tristimulus coordinates are normalised (ie Y=100 in the CIE system) then the point can be expressed in one less "chromacity coordinates". (eg (x,y), (a*,b*) ).
But a white point is still just that, a single point expressing very little information.  As well as that it means nothing outside its coordinate system (eg CIE 1931).
It is possible to alter the white point of a colour by performing a colour correction transform, but this is only a very rough estimate of how an object of that colour might appear under a different illuminant.  Multispectral imaging is required to reasonably estimate the appearance of an object under a differernt illuminant.
So leave it alone.  Certainly these articles need to be explained better, but I haven't got time to do it now.  If anyone wants to do it well, I suggest they have a read of:
"Billmeyer and Saltzman's Principles of Color Tecnology" by Roy S. Berns
TomViza 16:18, 17 March 2006 (UTC)
thread_title: No!

message: I don't support such a merge. These are two distinct but related topics, and are different enough to each merit their own articles. Color Balancing, once the white point is known, is not a fait acompli, and it has been demonstrated that color balancing may be more effective using a separate characterization for each taking/viewing illuminant pair. (See, e.g., "A Comparison of Different White Balancing Algorithms as Quantified by their Color Constancy," Proceedings of the SPIE, volume 5301, 2004.) Lovibond 02:20, 12 May 2007 (UTC)
replies: text: Well, first, you should leave the conversation at the talk:color balance page.  But my reasoning isn't really that the concepts are identical, but that they are so closely related that most of the article content would be mostly repeated, and it therefore is more useful to readers to have one article which discusses both, instead of having separate articles.  --jacobolus (t) 05:43, 12 May 2007 (UTC)
replies: text:  I'm not participating in any discussion on talk:color balance, so I can't exit that discussion. Fact is, the two topics are quite different. For example, white point plays a key role in the computation of color coordinates, such as L*, a*, and b*, which have little to do with color balance. Color balance can be performed without knowledge of the white point. I believe that merging the two articles would marginalize at least one of the concepts and foster confusion of the two ideas. Merging the two might have a small advantage to people (i.e., those performing gray balancing of digital color imagery) who have a fairly narrow view of the these two topics, but retaining cross-referenced articles would, IMO, enable a much broader view with minimal fuss. Isn't a broader view better for this forum? Lovibond 15:45, 14 May 2007 (UTC)
replies: text:  Er… "leave" as in "put", not as in "exit" --jacobolus (t) 21:56, 14 May 2007 (UTC)

text:  Lovibond, do you mind taking a crack at a better explanation for color balance then?  I don't think I properly understand the term as you're discussing it here.  --jacobolus (t) 23:40, 14 May 2007 (UTC)
thread_title: Proposed merge with Color Balance

message: This comment explains the edit I made to the section "White points and illuminants".
For general illuminants, there is no one-to-one correspondence between illuminants and white points. The correspondence is many-to-one.
The CIE D-series standard illuminants are an exception. For illuminants in the series, the chromaticity coordinates of the white points of these are calculated from the correlated color temperature using a formula. The spectral power distribution of the illuminant is in turn computed from its chromaticity coordinates. See  for the formulas. (In the reference, S_0(\lambda), S_1(\lambda), and S_2(\lambda) are pre-defined spectral power distribution functions.) 
The chain of derivation goes like this:
:correlated color temperature 
::→ white point chromaticity coordinates 
:::→ coefficients for combining S_0(\lambda), S_1(\lambda), and S_2(\lambda) 
::::→ the resulting spectral power distribution.
--71.185.180.254 (talk) 03:31, 13 January 2008 (UTC)
replies: text: Thanks. Sorry I was too quick on the revert trigger.  I should read the whole sentence, huh? Dicklyon (talk) 03:38, 13 January 2008 (UTC)
thread_title:  CIE D-series standard illuminants