Hi Yinz!
Is there any way to achieve a transparency map from houdini, the opacity filter does not seem to do the job.

Try enabling Opacity Falloff for the glass shader.

Enivob
Try enabling Opacity Falloff for the glass shader.

But that will actually change drastically the look of the shader. I am actually trying to figure out a way to achieve a kind of refractive map opacity filter, that basically shows me the refracted pixels of the empty background. I hope this make sense….

Eh, it does not change it that drastically and when faced with the option of having your alpha or not the choice is clear (a transparency pun…ha ha).

You should file this as a bug. I see what you mean, the alpha should be calculated correctly and Mantra is not doing that. Also, you could do two renders, one with Opacity Falloff enabled and another with it off. Then, in compositing, you could use the alpha from the first render to affect the alpha in the second one and keep your look. But you have to render twice if your look is “mission critical”.

Another option is to use a different external render engine. Renderman is free for non-commercial work.

Enivob
Eh, it does not change it that drastically and when faced with the option of having your alpha or not the choice is clear (a transparency pun…ha ha).

Good one (I allways appreciate such a transparent pun)
Yes, I guess I will file it as a Feature request. Of course this example is a more simplified version of the final illustration of the final shader and scene. I was hoping to find out some kind of obscure channel I could use for refractions but as you say it would be very nice to have the refracted background influence the alpha.