Hi
I am using sop volume and pyro to simulation fire in houdini 16.Use flame/pyro shader for density and temperature rendering.
The beauty pass looks beautiful based on the temperature channel in the dark backgroud but the alpha channel is based on the density. That makes it too transparent when I composite fire into a bright footage.The fire seems less and not obvious enough.When I turn the density channel into zero in the flame shader(because I don't need the smoke),the temperature fire can be rendered but the alpha is gone.
Does anyone know can I do to fix this problem?

The alpha for fire should be nearly zero, as flames are completely transparent. If the fire is not bright enough, make it brighter. Flames as rendered, to look nice and hot, should be 2 to 5 stops over exposed. To prevent them being a clipped white blob, you'll need to use a lut or grade with some highlight compression. Most film luts will give you plenty of range to do this.

in case you want to fake the alpha of the flame I believe you can use fire_mask AOV

Hi jsmack,

if the alpha for fire is zero,how can I composite fire with a bright video footage? no matter in nuke or AE, when I use the screen or add/plus mode, the fire will seem too weak because it loses a lot of darker detail? That's the real problem I want to solve~

Hi tame,

Thanks again for your reply. I've try the fire_mask AOV. but there are some question.
1 If I use a shelf tool to make a explosion, the fire mask aov is fine.
2 If I make fire,and then to tweak the shader curve of temperature(without heat channel),the beauty of the fire is good but the fire mask AO is grainy and noisy. Besides it is also too transparent.
3 If I only use volume to create density and temperature field in sop for fake fire, fire mask aov can not be rendered.