This page provides information about the V-Ray A Color Operation Texture.


Overview

The VRayAColorOp texture performs an arithmetic operation between two colors and/or textures. This texture is useful for blending textures and colors without the need for a separate V-Ray Blend material.

In the example here, the candle holder is shaded with a V-Ray Material that is set up to imitate brass.  We also add a Coat layer, where we apply a VRayAColorOp texture. For Color A, we apply a V-Ray Curvature texture and set its Mode to Concave. For Color B, we add a green-blue color to imitate patina. We set the Mode of the VRayAColorOp to Sum. This way, we have a base of a brass material, and we are adding a layer of a colored Curvature texture on top, which imitates weathering of the brass. Without the VRayAColorOp texture, we would need to create two separate materials - one for the brass and one for the patina and attach them to a V-Ray Blend material.




Inputs

Color A – Specifies the first color. A Texture can also be applied, and it can be blended with the color using the Mix Strength parameter.

Mult A – A multiplier for Color A.

Color B – Specifies the second color. A Texture can also be applied, and it can be blended with the color using the Mix Strength parameter.

Mult B – A multiplier for Color B.

Alpha from Input – When enabled, the alpha value is derived from the Color A shader. In case the Mode is set to Result B, the alpha is derived from the Color B shader.

Result Alpha – Determines a value that overrides the alpha value in the output.

Mode – Specifies the calculation method for the two colors/textures. The selected mode determines the data being output when the Output parameter is set to Default. 

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



Outputs

Output – Determines the data that the texture outputs to the material. Most of the options in the dropdown are identical to the ones in the Mode parameter. Here are listed only the options that are unique to the Output.

Default – Outputs the data determined by the Mode parameter.
Red – Outputs the red color channel from Color A. If the Mode is set to Result B, then the red channel from Color B is output.
Green – Outputs the green color channel from Color A. If the Mode is set to Result B, then the green channel from Color B is output.
Blue – Outputs the blue color channel from Color A. If the Mode is set to Result B, then the blue channel from Color B is output.
Alpha – Outputs the Alpha channel of the texture.
Intensity – Outputs the intensity value from Color A. If the Mode is set to Result B, then the intensity from Color B is output.



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