[Radiance-general] colorpict and materials

[Lars O. Grobe]

Hi!

> Ok, lets jump into the ring :-)
> Hmm, maybe Lars want three things at once:
> 1) get the physics right
> 2) preserve the average color appearance of the material base
> 3) add the additional color variation from the map without disturbing 
> 1+2 in the average..

Yes!!!! That is what I was not able to describe ;-)))

> On the other hand, multiplying a color pattern onto a colored base 
> will hardly ever produce anything which one expects at first glance, 
> an extreme example: if you have a red base with r/g/b = 0.2 / 0.02 / 
> 0.0 you can multiply in maps like mad and will never get something 
> blue into the picture.

Yes, this is true, I was just guessing that it can't be that easy ;-)

> I think that Lars wants some sprinkles and streaks and dots of blue 
> added to the base here and there, but so little in covered surface, 
> that the average color and thus the brightness of the base does not 
> suffer much.

That (the average) is necessary, while the details (e.g. those famous 
sprinkles and streaks and dots would be nice).

> What about the following: (yeah, again one of my weird ideas:-) edit 
> the picture (resp. the red parts of it) with some color tool in an 
> image manipulation program like Gimp such that the average rgb values 
> for the dominating parts of the pic are those of the plastic 
> description, then it could be used as colorpict to a new plastic with 
> rgb=1/1/1. This new combination will more or less have the same color 
> (in the spatial average) as the original base material, but still look 
> like the pattern.

In fact, I hoped that this could be somehow done with the radiance 
tools in a script, I just don't know how. It's similar to what normpat 
is doing, only it doesn't normalize to 1/1/1, but to R/G/B values I 
know as the average material color (->brightness). I think I will have 
to take a look at normpat to find out how it does that in detail - 
would be a nice tool if it could bring pictures to (known) color values.

Thanks, CU Lars.
--
Lars O. Grobe
grobe at gmx.net