6.1 Pigment

Let us first discuss the PIGMENT_STMT. In its simplest form it just specifies a color C

  pigment { color C }

Beside rgb <R,G,B> for $C$ we can also use rgbf <R,G,B,F>, rgbt <R,G,B,T> and rgbft <R,G,B,F,T>.

The value $F$ in the first variant is the filter parameter $0\leq F\leq 1$. It specifies the amount of light of color $\langle R,G,B\rangle$ which may transmit through the object. E.g.

	 rgbf <1,0,0,0.25>

means that 25% of the red component of light passes through the object and nothing of the green and blue components. Thus the object acts as red filter. Note however, that the amount of filtering does not depend on the thickness of the material, see media (7.2) for how this can be made more realistic.

The value $T$ in the second variant is the transmit parameter $0\leq T\leq 1$. It specifies the amount of light the can pass unfiltered through the object. The remainder part $1-T$ is used for the color $\langle R,G,B\rangle$ of the object, e.g.

	 rgbt <1,0,0,0.25>

means that 25% of the light will pass unfiltered though the object and 75% of red will be added to this light.

Of course, usual objects will not have a homogeneous color but some patterns, which we have to treat next.