[Radiance-general] Re: mixpict applied to files from tmesh2rad

[Greg Ward]

Bernhard Spanlang wrote:
> I'm using tmesh2rad to generate smooth surfaces for rendering in
> radiance.  tmesh2rad allows to apply a colorpict pattern to the
> surface.  Now I want to have a transparency value (alpha channel)
> for each colorpict RGB value.  In the workshop it was mentioned a
> few times that mixpict could be used for this and I know Carsten
> has written a patch that allows to load colorpictures with alpha
> channel.
>
> If I create a radiance file with tmesh2rad can I add transparency
> from an additional grayscale image (alpha values) using mixpict ?

Just put the transparency layer into a grayscale TIFF and covert to 
Radiance with ra_tiff -r, then use this picture in a mixpict.  If you 
are mixing the surface material with nothing (as in a ghostly object), 
you would mix the material with the "void" placeholder.  If you want to 
mix a pattern with nothing, then do the same but with the pattern 
rather than the material.

void mixpict alpha_mix
7 my_material void green alpha.pic picture.cal pic_u pic_v
0
0

I use the "green" function above rather than "grey" because it arrives 
at the same value with less computation for a grayscale picture.  
Obviously, you should replace the "picture.cal" and "pic_u" and "pic_v" 
file and variables with whatever matches your original pattern in order 
to get them to match.

Corrections to follow, no doubt.
-Greg