Fire Opacity Mode | fire_opacity_mode – While smoke has its own opacity in the Smoke Opacity rollout, fire's opacity can be determined in either of three ways:
Use Smoke Opacity – Fire will use the same opacity that is set to the smoke in the Smoke Opacity rollout. This way the fire will not be visible in cells where there is no smoke.
Fully Visible – Fire will always render as if it has full opacity, but will not produce alpha. This way fire will be visible even in cells that have no opacity. This mode is intended for use with Phoenix simulations, such as simulations with sources that emit Temperature but do not emit Smoke. During rendering, Phoenix internally composes the fire with the scene using additive blending, and such blending must be used when compositing fire manually. However, this mode is not suitable for compositing fire mixed with smoke.
Use Own Opacity – A varying opacity can be set for the fire using the Opacity diagram.
Opacity Texture Mode | mod_et – Visible only when the Fire Opacity Mode is set to Use Own Opacity.
Don't Use Opacity Texture – The Fire Opacity is based entirely on the Intensity/Opacity Curve below.
Multiply Opacity By Texture – The Intensity/Opacity Curve is multiplied by the specified texture to produce the final Fire Opacity.
Fire Opacity From Texture – The Fire Opacity is based entirely on the specified texture - the Intensity/Opacity Curve is ignored.
Physically Based | blackbody – Transitions between artistic look of the fire (when set to 0) and realistic physically based Intensity (when set to 1). The realistic mode multiplies the fire intensity by the Black Body Radiation model, which gives strong brightness to the hot parts of the fire. The example below uses the settings from the miniature image on the right. For more information, see the Physically Based example below.