The color usage in OctaneRender® is spectrum-based, using the wavelength of visible light. All RGB inputs that you use in other areas are converted to a specific wavelength of a given RGB color. RGB values themselves are just an approximation of an actual, true color — color is light, after all — therefore, the most precise definition of a given color is its own actual light wavelength. RGB is not a precise method to calculate color and can actually fail when used for bright emission. For this reason, the Gaussian spectrum node is recommended instead.


GAUSSIAN SPECTRUM NODE


How to Use

This node allows enables the creation of colors using the Gaussian spectrum distribution curve (or Normal Distribution). As there is no spectrum-based color picker in Cinema 4D, there is no graphical user interface to assist in picking colors with the Gaussian spectrum node. The image below illustrates the visible spectrum with wavelength values:



Note that ultraviolet (blue) is on the left side of the spectrum and infrared (red) is on the right side. The opposite is true for the Kelvin (color temperature) scale. 


Octane remaps the Wavelength, Width and Power values of the Gaussian spectrum into a range from 0.0 to 1.0. As a result, entering in an actual wavelength value directly from the Gaussian spectrum will not give the expected results. To make it easier to get the desired color, we have put together a simple Cinema 4D scene, consisting of a Cube Object with an Octane Diffuse material applied; a Gaussian Spectrum node is piped into the Diffuse input of the material. Launch Live Viewer and make adjustments to the Wavelength, Width and Power values to dial in the color you need, then copy that node into your material or light in the Texture slot. You can pop out the Attribute panel and lock it the Gaussian spectrum node to make your adjustments, if you wish. Use that scene as you read through the rest of this topic.


Node Setup

First, open the Node editor and prepare the setup as seen in the image below. You can connect this node to any color inputs of the other channels. 


Gaussian Spectrum node with Materials



Gaussian Spectrum Settings

Wavelength   

As Scott Benson notes in his excellent Lights and Emission in Octane for Cinema 4D article, Wavelength is roughly the same as Hue in the HSV color model, though not completely. This represents the mean wavelength approximation between 380nm – 720nm, which Octane remaps into 0.0 to 1.0. The lower wavelength values will be in the blue range while higher values be in the red range. 

Width   

The Width value controls the prevision of the resulting color as set in the Wavelength value, from fully saturated to white-ish. Width is not exactly the same as Saturation in the HSV color model, as there are interdependencies with both the Wavelength and the Power values. You can imagine this width value as a spread, from black at 0.0, and completely faint at 1.0. Scott Benson recommends using the value of 0.05 for the width, as this gives a narrow-enough result. Some wavelength values do better with this recommendation than others, so keep that in mind.

Power   

You can control the brightness from here.


As Octane is dealing with Wavelengths, Width and Power, simple discreet color choices (such as RGB blue 0,0,1) or HSV blue (0.66667, 1, 1) can be a little less intuitive (for those who have been using computers to pick colors for any real length of time). These models and others are mere approximations of the actual colors that we see, which the Gaussian spectrum  accurately describes.