trouble with colourpict

radiance-general
1

I was hoping someone on this list might be able to help me. I am using rayfront 1.02
and I cant seem to get the colourpict pattern to work correctly as a pattern.

The scene has a wall which has a red plastic material applied to it.
Then a corg.cal texture was applied. the defenition is shown below.

void texfunc corrugated_wall
6 x_pert y_pert z_pert function/corg.cal
    -rx 90
0
1 0.075

Then i created a pattern using the picture.cal file using the definition below.

void colorpict logo1
15 fadered fadegreen fadeblue images/arco.pic function/picture.cal pic_u pic_v
    -rx 90 -rz 180 -t 4 0.0 1.3
0
4 1 1 1
                1

The problem that i am having is that the image only appears as a brightness function
of the red wall (i.e. a monotone image)

Does anyone know how I can get the picture to be a colour image on the wall.

The image was saved in Photoshop as an 8-bit RGB image and converted to a pic file
using ra_tif

Russell

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2

Russell Maunder wrote:

I was hoping someone on this list might be able to help me. I am using
rayfront 1.02 and I cant seem to get the colourpict pattern to work correctly
as a pattern.
....

Russell,

Has the the explanation I sent through the Radiance-Support
mailing list not arrived downunder yet? Modifiers just multiply
their values with the material values. And a multiplication based
on blue/green material values of zero will simply give zero again.
You want to use a white base material, and a red logo picture.

-schorsch

···

--
Georg Mischler -- simulations developer -- schorsch at schorsch.com
+schorsch.com+ -- lighting design tools -- http://www.schorsch.com/

3

Georg Mischler wrote:

Russell Maunder wrote:

> I was hoping someone on this list might be able to help me. I am using
> rayfront 1.02 and I cant seem to get the colourpict pattern to work
> correctly as a pattern.
> ....

Russell,

Has the the explanation I sent through the Radiance-Support
mailing list not arrived downunder yet? Modifiers just multiply
their values with the material values. And a multiplication based
on blue/green material values of zero will simply give zero again.
You want to use a white base material, and a red logo picture.

Looking from a more general point of view:

If you want a *full color* picture without a tint from the
color of the surrounding wall, then you have two basic choices.

One would be to add a polygon to your model for holding the
picture, which gets a white material.

If you want to avoid the modelling effort, then you'll have to
manipulate your picture, so that it's color values compensate for
the color values of the base material. Of course, this only
works if the rgb values of the material are all non-zero, or you
will run into the multiplication-by-zero dilemma. Seems like the
polygon solution will be simpler in most cases.

Actually, you could combine the two approaches, by defining
a mixfunc which selects the red plastic for the surrounding
area, and a white plastic with the colorpict in the picture
area. Mixtures are the exception to "normal" modifiers, in that
they can actually replace material values according to their
functional criteria, instead of just modifying (sic!) them.

Rayfront makes the use of mixtures exceptionally easy, after all,
and the function for this task is trivial:

  if(and(inside(X0,Px,X1),inside(Z0,Pz,Z1)),1,0)

If you replace X0, X1, Z0, Z1 with the lower and upper X and Z
boundaries of the image, then you can write this directly into
the expression field of the mixfunc dialog. If the image is
aligned to the YZ-plane, then you'll have to adapt accordingly.
The white plastic and colorpict will now go into the foreground
slot, and the red plastic becomes the background.

-schorsch

···

--
Georg Mischler -- simulations developer -- schorsch at schorsch.com
+schorsch.com+ -- lighting design tools -- http://www.schorsch.com/