I am trying to render fire in Houdini.

When I check “render view” in Houdini I've see:


But when I try render to tif-file, I see nothing:


I have tried to create a new file and make same conent again, but same result.

Can anybody explain me where I am wrong? Thank you.

I'm not an expert in compositing, but the short explanation is that the opacity is zero (or close to zero), because emission doesn't block anything behind it. However, many programs reasonably assume that opacity must be applied to the image when viewing, meaning that the colour doesn't contribute anything. Mantra and many other 3D renderers output TIFF files with opacity already applied to the colours so that emission will automatically add, instead of needing infinite values to survive an opacity of zero. If you open the TIFF file in MPlay, it will show up correctly. Full compositing can require additional image planes for emission, but this at least handles one simple case, at the expense of having many programs not related to rendering display them incorrectly.

Hopefully there won't be a flame war about premultiplied vs. unpremultiplied opacity following this comment, 'cause it does seem to be a contentious issue.