Alpha Channel problem

Hi Creatives,

i struggle with generating an alpha channel in my filters.
I see some surface filters that have alpha channels available, others not.
Why is that? What do i have to do in the result component to make the alpha visible and selectable via the Filter tab?

(I know what alpha channels are and how to use them in 3d applications )

Thank you!

Thanks for your fast answer.

I am editing an existing filter (here: Choubpaek - form MISC texture filters) and want to give it an alpha channel.
For example: I want to generate a kind of grate filter out of it using the background as alpha - i only want to see the grate.
I could use 'height" or a threshold of height as an input for the alpha. Do i have to use "set alpha" to make the alpha channel available in the filter use?
I hope i made it more clear now

P.S. got it now! I have to use "Set alpha" and combine it with the source of the result to get a working alpha channel

Thanks a lot!

Then if you are using FF10 go to Image-Blank and click on the fill color and change the alpha to zero..........
This will give you the transparent background in conjunction with using the alpha in the filter itself....

You are welcome, glad that I could help......
You could also use the alpha for many elements in the filter to build up parts of the final result...Such as the picture below the filter uses 2 images and each has a separate alpha and blends together in the blend component for the final result....Its just another use for the alphas.......