[Radiance-general] colorpict and materials

[Lars O. Grobe]

Hi,

sorry, so again, I try to be clear in asking this time ;-) By the way, 
have nice holidays (I hope that's the reason for your travel ;-)!

All is about the question how to map pictures onto a surface without 
corrupting its material properties. I understand that colorpict 
multiplies the material color components with those of the picture.

If I have a grayscale image processed by normpat (which means that the 
average gray value is 1.0) and apply it to a material, the overall 
color and brightness will remain the same. So I get the "pattern" from 
the image, but the surface still has the correct material properties 
(color, brightness etc). I used this so far.

Now I want to use a colored picture for mapping. I also apply normpat 
to it, so, as far as I understand, the average of all R, G and B must 
be 1.0, right? For example, I use a normpat'ed picture of green marble. 
I than apply this using colorpict to a surface, which has a "marble" 
material. Will the overall color and brightness still be that of the 
defined material, as the picture map has the average of 1.0?

The background: I try to use exact data for material definitions, but 
the image maps can't all be color corrected. So I want the overall 
color and brightness from defined materials, e.g. from the plastic 
material, and use the map only for what I would call "local color 
variation". The reason is that I have e.g. red marble, got its color, 
brightness and all that defined as plastic marble. But the marble has 
blue particles which won't appear if I use a grayscale imagemap. So I 
want to use a normpat'ed (NOT colorcorrected e.g. by macbethcal!) to 
bring these blue parts onto the surface. The whole surface however must 
still have the average color of my plastic marble material.

If I understand the man-page of normpat, that's just what it was 
invented for. However, I am a bit unsure, as all Radiance documentation 
uses colorpict with a bright white material.

TIA+CU, Lars.
--
Lars O. Grobe
grobe at gmx.net