RE: Color By Frequency

[Macy]

GREAT SYNOPSIS!

Where in the 'color' chart does the folowing phenomenon fall? Paint a wheel 
half black and half white. As the wheel spins faster and faster, the eye 
perceives the wheel to be colored.

Is there any insight into better understanding of color perception with the 
'wheel experiment' in mind?

Or, does this observation just fall under the, "Oh, that's interesting," 
heading?


--- address@hidden wrote:

From: mmesser314 <address@hidden>
To: address@hidden
Subject: RE: Color By Frequency
Date: Thu, 12 Jan 2012 13:31:53 -0800 (PST)


Jordi Gutiérrez Hermoso wrote
> 
> I'm not a lawyer, but I'm pretty sure that algorithms don't have
> owners (i.e. copyright). An expression of it (i.e. code for a specific
> language) does. If you wrote the algorithm based on other code, your
> version of it could be considered derivative work and fall under the
> copyright of the original code. But if this is not the case, you
> saying that you learned the algorithm somehow and telling us your
> rendition of the algorithm is GPLv3, that's good enough for us.
> 
> It would be nice to tell Dan Bruton that we're using his algorithm
> in Octave, but it doesn't seem to me strictly necessary to get this
> into Octave.
> 


William Krekeler wrote
> 
> I'm not a lawyer either, I'd just rather 'play nice '. If the algorithm
> was the normal read a paper, then download the requisite 30 background and
> cross-referenced papers to understand what was read before you can
> implement the suggested solution, I would agree completely with you.
> However, Dan published some code (I think Fortran) which I converted to
> Octave/Matlab and wrote a few test cases to confirm that it worked. A
> lawyer is likely going to argue that the Octave code is a derivative work
> and the source should be given the opportunity to weigh in. I chose to
> contact him to give him that opportunity.
> 
> William Krekeler
> 

The conversion from wavelength to RGB is not a mathematical alogrithm that
can be derived from a set of universal axioms. The output is an
approximation of the response of a human eye to a given input. It is based
on measurements of eye responses. Any particular approximation is based on a
particular definition of R, G, B, white (or illumination), and non-linear
corrections (or gamma).

The  http://www.cie.co.at/ CIE  standards body has published eye responses
of a standard observer, defined various ways of converting a given reponse
to values representing a color, and published the color numbers for
monochromatic light at all visible wavelengths. No license is needed to use
this information. 

Wading through this information, choosing R, G, B, illumination, and gamma,
and deriving the math of converting wavelength to RGB is not trivial.
Apparently Dan Bruton has done it. At least, he has published 
http://www.physics.sfasu.edu/astro/color/spectra.html code  that does some
sort of conversion. If William Krekeler has adapted this code, his work is
clearly derivative. Because of this, I expect he would need permision to
publish it. If he had done the work himself, I expect he would not need
permission, regardless of how closely his work parallels other work. But I
am not a lawyer either.

It seems very likely that Dan Bruton does not mind if people use his code.
He apparently published it so people would use it. He put his name in the
code, but no copyright notice. His  http://www.physics.sfasu.edu/astro/
website  contains a link to an article favoring freedom of speech over
copyright enforcement. Still, asking permission and acknowledging
contributions are entirely appropriate. 

Note that his code does not mention his choice of R, G, B, illumination, or
gamma. As long as William is talking to him, it might be good to ask him
what these are and add a comment describing them to the code. 

William might also note the limitations of this conversion. RGB is good at
describing the colors that can be produced by a monitor. The human eye is
sensitive to more colors than this. We can see colors that cannot be
described by positive RGB numbers. As it happens, none of the pure spectral
colors can be represented given the usual parameter choices. For more
information, see this 
http://stackoverflow.com/questions/1472514/convert-light-frequency-to-rgb
stackoverflow article  or this 
http://en.wikipedia.org/wiki/CIE_1931_color_space Wikipedia article . 



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