[Radiance-general] pcomb-masking color channels

[Humann Chris]

Dear group,

I'd like to be able to generate two separate images from an HDR image  
of the sky vault: one with blue sky; the other with clouds and sun  
(assuming it's not occluded).  I'm not well versed in the usage of  
'pcomb' but I'm assuming I'll need to somehow create a mask based on  
both color and brightness thresholds.  It seems from my archive search  
that a call to 'pgblur' with a high radius might help in defining  
sharper boundaries between clouds and blue sky. (http://www.radiance-online.org/pipermail/radiance-general/2008-May/005046.html 
)

Has anyone been successful in achieving something similar?

As always, thanks!

Chris