[Radiance-general] pcomb to clip specific colors

[Humann Chris]

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
LOISOS + UBBELOHDE
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1917 Clement Avenue  Building 10A
Alameda, CA  94501 USA
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510 521 3800 VOICE
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www.coolshadow.com



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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