I have been building a scene with emissive materials and rendering with Karma. In the viewport everything was working correctly, but when it came time to generate an animated sequence I was really stumped as to why my emissive materials were not 'emitting' in the final output render. Using Karma and MaterialX shaders with a geometry parameter connected with emission.

After much searching and option clicking I found that I needed to add an 'Extra Render Var' in the Karma Render Settings and include the attribute source name which in my case is 'emitint'. It doesn't seem to matter what parameter/pass name you create or select and I am just outputting a .png sequence. Format is float, Data type is 3f and Source type is Primvar.
Not sure if it is the proper way to enable emission but once I did this I was able to get emission to show up in my final renders. What the heck? Why visible in the viewport but not in the output?

Hope this helps anyone who may be experiencing the same issue.

I am sure there is a good reason for this as there always is for all things Houdini. I am wondering why the viewport defaults would be different from the render output defaults or if I am missing something else in my setup ?

Jeff