This page provides information about the Color Arithmetic node in V-Ray Node Editor in Blender.


Overview

The Color Arithmetic node performs an arithmetic operation between two colors/textures.

For the example here, a Bitmap node is attached to Color A, and Color B is set to an orange color. The Mode is set to output the Product of the two Color slots, and it is connected to the Diffuse of the V-Ray Material, resulting in an orange-tinted brick map.



Properties

Mode – Specifies the calculation method for the two colors/textures: 

Result A – Returns the value of A (color_a*mult_a)
Result B – Returns the value of B (color_b*mult_b)
Product – Performs a multiplication operation and returns the product (A*B).
Sum – Performs an addition operation and returns the sum (A+B).
Difference – Performs a subtraction operation and returns the difference (A-B).
Power – Performs an exponentiation operation and returns the power (A^B).
Division – Performs a division operation and returns the quotient (A/B).
Minimum – Performs a comparison and returns the minimum value.
Maximum – Performs a comparison and returns the maximum value.
Absolute Difference – Performs a subtraction operation and returns the difference as an absolute value (abs(A-B)).
Lower Intensity Color – Returns the value of whichever Color parameter has the lowest intensity.
Greater Intensity Color – Returns the value of whichever Color parameter has the greatest intensity.  
Sin – Performs a sine function and returns the result (sin(A)).
Cos – Performs a cosine function and returns the result (cos(A)).
Abs – Returns the absolute value of the first argument (abs(color_a*mult_a)
Ceil – Performs a ceiling function that rounds up to the next integer that is equal to or greater than the largest argument - A or B (ceil(A)); (ceil(B)).
Exp – Performs an exponential function (ea+b).
Floor – Performs a floor function that rounds down to the next integer that is equal to or smaller than the smallest argument - A or B (floor(A)); (floor(B)).
Log – Performs a natural logarithmic function (ln(A)).
Log 10 – Performs a common logarithmic function (base 10) on the first argument (log(A)).
Sqrt – Performs a square root function (√A).
Fmod – Performs a division operation and returns the remainder (A%B). 
Average – Returns the average of A and B (((color_a*mult_a)+(color_b*mult_b))/2)
Tan – Performs a tangent function and returns the result (tan(A.0)).
Asin – Performs an arcsine function and returns the result (asin(A).
Acos – Performs an arccosine function and returns the result (acos(A)).
Atan – Performs an arctangent function and returns the result (atan(A)).
Atan 2 – Performs an arctangent function with two arguments and returns the result (atan2(A,B)).
Bias Schlick – Performs a faster bias approximation, described by Christophe Schlick, based on the original definition by Kenneth Perlin.1
Gain Schlick – Performs a faster gain approximation, described by Christophe Schlick, based on the original definition by Kenneth Perlin.2
Bias Perlin – Implements the original bias definition by Kenneth Perlin.3
Gain Perlin – Implements the original gain definition by Kenneth Perlin.4

Color A – Specifies the first color/texture.

Color B – Specifies the second color/texture.

Multiplier A – A multiplier for Color A.

Multiplier B – A multiplier for Color B.




Bias and Gain Equations

The exact equations for the Christophe Schlick and Kenneth Perlin definitions are:

  1. bias_schlick(x, a) := x / ((1 / a - 2) * (1 - x) + 1)
  2. gain_shclick(x, a) :=
  { bias_schlick(2 * x, a) / 2 , if a < 0.5 }
  { (bias_schlick(2 * x - 1, 1 - a) + 1) / 2 , if a >= 0.5 }
  3. bias_perlin(x, a) := x ^ (ln(a) / ln(0.5))
  4. gain_perlin(x, a) :=
  { bias_perlin(2 * x, 1 - a) / 2 , if a < 0.5 }
  { 1 - bias_perlin(2 - 2 * x, 1 - a) / 2 , if a >= 0.5 }


References

[*] Kenneth Perlin and Eric M Hoffert. Hypertexture. SIGGRAPH, 1989.
[*] Christophe Schlick. Fast alternatives to Perlin’s bias and gain functions. Graphics Gems, 4, 1994