[Radiance-general] Colorpict question

Bleicher, Thomas T-Bleicher at bdp.co.uk
Mon Mar 26 10:29:39 CEST 2007


The idea is to define a pattern in step 2 and use this
pattern as a base for the material definition in step 3:

void colorpict pattern1
7 red green blue picture_norm.pic picture.cal tile_u tile_v

pattern1 plastic material1
5 0.4 0.4 0.4 0 0

This will create 'material1' with an average reflectance
of 0.4. You can use 'material1' directly in your scene, there
is no need to define an alias.

Using a normalised picture allows you to change the material
reflectance by changing the rgb-arguments in the plastic
primitive (here: 0.4) directly. You don't have to take into
account the average of the picture as well because the average
of the normalised image is 1.

You don't have to use a digital image as source (normpat will
take care of that, too). Only if you want to use the image
as illumination source you need a properly calibrated HDR image
which can only be obtained with a digital camera.

I have a few comments on image maps here:



> -----Original Message-----
> From: radiance-general-bounces at radiance-online.org 
> [mailto:radiance-general-bounces at radiance-online.org] On 
> Behalf Of cveleglg at bankerinter.net
> Sent: 26 March 2007 08:18
> To: radiance-general at radiance-online.org
> Subject: [Radiance-general] Colorpict question
> Hi,
> I want to define a material with colorpict pattern, and I 
> plan to use non calibrated digital photos of a material 
> sample taken by ordinary camera.
> If I know the average reflectance of the real material (r ,g 
> ,b) is the material defined with next procedure physically correct:
> 1)normalize photos average brightness with normpat 2)use it 
> in a colorpict primitive:
> void colorpict pattern1
> 7 red green blue picture_norm.pic picture.cal tile_u tile_v
> 1 A1
> 3)define basic material with the average grey reflectance as 
> a real material:
> void plastic mat1
> 5 grey(r,g,b) grey(r,g,b) grey(r,g,b) 0 0
> 4) define alias:
> pattern1 alias mat_with_pat material1
> I've read previous posts on similar topics, but most of the 
> images mentioned were already calibrated, so I'm not sure if 
> resulting material in my example would have appropriate 
> appearance (pattern) and still appropriate reflectance (basic 
> material). Of course I don't expect to obtainr 100% accurate 
> reflectance in each point of the material :)
> Thanks,
> Marija
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