[Radiance-dev] Ray Parameters

[Marcus Jacobs]

Dear Group

I am seeking to make a minor modification of the Radiance source code to 
solve an issue that I am having with my renders. The issue that I am trying 
to resolve is the color shift (i.e. color bleeding) that occurs. My goal is 
to allow for me or anyone else to wishes to utilize the added functionality 
to gain some artistic control on the amount of color bleeding that occurs 
without invalidating the physical accuracy of the result. I have been able 
to accomplish this in RADZILLA by utilizing its alternate ambient material. 
I have an idea which may accomplish the same goal in classic Radiance.

In rayinit.cal there are many variables (i.e. Dx, Dy, Dx, Lu, Lv, etc.) that 
are available to the user for use in function files. What I would like to do 
is to gain control of the ray type parameter (rtype) defined in ray.h. The 
basic concept is that in a function file associated with colorpict or 
colorfunc, if the ray type is equal to anything excluding an ambient ray, 
the color will remain unchanged. If the ray type is an ambient ray, the 
color could be defined by the user.  I have created my own function file 
,colorshift.cal, which would define the ambient color of a material as:

red = (1- B4) * grey(B1,B2,B3) + B4*B1;
green = (1- B4) * grey(B1,B2,B3) + B4*B2;
blue = (1- B4) * grey(B1,B2,B3) + B4*B3;

where B1, B2, B3, B4  is the color's red, green, blue components and color 
bleeding factor (detemined by the user) respectively. This will have the 
effect of desaturating the color according to the color bleedig factor 
without altering its overall reflectance (i.e. grey(r,g,b) will remain 
constant). I have done some research in func.h and func.c to see how I might 
gain some control over the ray type parameter. I have not had much luck in 
completely understanding how the code works. I am assuming that many of the 
standard parameters listed in rayinit.cal are extracted in the function 
chanvalue. One problem that I am having is that I can find where this 
particular function is being called elsewhere in the source code. Any 
insight as to how to accomplish my goal would be greatly appreciated.

Regards,

Marcus Jacobs