[Radiance-general] RGB to Radiance definition

[Germán Molina Larrain]

Thanks very much, Greg! I will have that in mind... I guess the "rendering"
issue may be misleading when sharing the models. It is OK for now, I guess.

And, Yes! That is an awesome presentation! Really really cool tips, facts
and images.

Best,



2016-06-24 20:32 GMT-03:00 Greg Ward <gregoryjward at gmail.com>:

> By the way, I love your presentation, Mark.  Would it be OK to link it to
> radiance-online.org (rather than having it buried in an obscure mailing
> list thread)?
>
> -Greg
>
> > From: Mark Stock <mstock at umich.edu>
> > Date: June 23, 2016 9:35:47 AM PDT
> >
> > The slides referenced in that thread have moved (apologies!) to here:
> > http://markjstock.org/doc/gsd_talk_11_notes.pdf
> >
> > The particular slide with my very unscientific RGB-to-reflectance
> > conversion contains:
> >
> > Start with an RGB color from whatever color picker you use
> > (249, 214, 172)
> > Normalize 0..255 to 0..0.9
> > (0.88, 0.76, 0.61)
> > Square it (to move medium gray of 0.5 closer to grey card grey of 0.18)
> > (0.77, 0.57, 0.37)
> >
> > I hope this helps.
> >
> > Mark
> >
> > On 6/23/16,  <> wrote:
> >> Hello Germán,
> >>
> >> Have a look at Mark Stocks comment on converting RGB values
> >>
> http://www.radiance-online.org/pipermail/radiance-general/2011-April/007743.html
> >>
> >> Regards
> >>
> >> Terrance
> >>
> >> On 23/06/2016 4:00 am, Germán Molina Larrain wrote:
> >>> Dear All,
> >>>
> >>> I am trying to integrate easier ways of defining materials in
> >>> Groundhog, for which I have the following doubt. How can I define a
> >>> Radiance material (i.e. plastic, metal, glass, etc.) from an RGB
> >>> combination and the global Reflectance (transmittance)? The purpose of
> >>> this is to enable "eyedropping" a color, and assigning a reflectance
> >>> or transmittance to it.
> >>>
> >>> What I initially did was to find the combination of RGB reflectances
> >>> that satisfied the rho = R*0.265 + 0.67*G + 0.065*B while maintaining
> >>> the original proportions of RGB. However, since the RGB color that
> >>> comes from the eyedropper has Black/White components (which intend to
> >>> emulate shadows and different light exposures), my procedure often
> >>> ends up returning an R, G or B channel that is greater than 1.
> >>>
> >>> I guess my question is: Is there any way of reconstructing the R, G
> >>> and B reflectances (or transmittances or whatever) from an RGB pixel?
> >>> Maybe playing with HSL space or something?
> >>>
> >>> Best,
> >>>
> >>> Germán
> >>>
> >>>
> >>
> >>
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> >>
> >
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