Ah, yes I see, and it certainly adds a level of speed and flexibility. It's different.

We don't really do volumetrics either, it's particles that cover the areas in a way to mimic volumetrics. I guess you could say it's a hybrid between real volumetrics and your still images.

By-the-way, if they are in Jpeg, how do you manage to put transparency on it?  or do you rather use the same image as both the color channel (greyscale clouds) and the opacity mask?

Would you let me have a sample to play with in PD Howler? like to place it behind our mountains?