[Radiance-general] pcomb to clip specific colors

[Thomas Bleicher]

Chris

Not directly responding to your question but here is an alternative
approche:

Instead of assigning different reflective colors to the facades you are
interested in you could just separate each facade direction into a
dedicated octree and run a simulation with white light. Renderings should
be fast if you restrict yourself to a single mirror reflection and no
ambient contribution.

You can then add up all the images for a single time step to get the
combined direct reflection. If you want to highlight a particular part you
can add/mix the individual pictures with a color in the post-process.

Regards,
Thomas


On Wed, Jan 16, 2013 at 2:44 PM, Humann Chris <chris at coolshadow.com> wrote:

> Thanks for the quick response Greg!
>
> I'm using a specific, specular reflective color on each facade orientation
> of a building to better understand which curtain wall orientation is
> contributing to direct solar reflections on the street level. I'm trying to
> parse from each image in an annual, time lapse series the resultant
> patterns of reflection on the street separately for each orientation /
> color.
>
> Running the script you sent I'm getting the following error:
> is_yellow: undefined function
>
> Thanks again,
> Chris
>
> Christian Humann ~ Associate
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>
>
> On Jan 16, 2013, at 11:08 AM, Greg Ward wrote:
>
> Hi Chris,
>
> I'm not sure I understand what  you're after, exactly.  The following will
> turn all pixels black except those with a nearly-zero blue channel and
> non-zero red and green channels:
>
> pcomb -e 'and(a,b):if(a,b,a)' -e
> 'ypix=and(.01*ri(1)-bi(1),.01*gi(1)-bi(1))' -e
> 'ypix=is_yellow(ri(1),gi(1),bi(1))' \
> -e 'ro=if(ypix,1,0);go=if(ypix,1,0);bo=0' input.hdr > output.hdr
>
> The and() expression returns positive if both red and green channels are
> more than 100 times the blue channel.  We can't compare blue to zero due to
> limitations in the accuracy of RGBE pixel values.
>
> -Greg
>
> *From: *Humann Chris <chris at coolshadow.com>
> *Date: *January 16, 2013 10:47:38 AM PST
> *
> *
>
> Dear group,
>
> I would like to use 'pcomb' to clip yellow reflections (r,g,b=1,1,0)
> coming off of the same colored mirrored glass on a facade system and write
> to a new image such that only these reflections are shown.  I thought I'd
> pestered the group enough times on 'pcomb' matters to figure this out using
> the many great responses I've received over the years, but the right syntax
> is eluding me now.
>
> As always,
> Thanks!!
>
> Christian Humann ~ Associate
> *LOISOS *+* UBBELOHDE*
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 1917 Clement Avenue  Building 10A
> Alameda, CA  94501 USA
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> 510 521 3800 VOICE
> 510 521 3820 FAX
> - - - - - - - - - - - - - - - - - - - - - - - - - - -
> www.coolshadow.com
>
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