Need Help in Nuke Alpha Masking & Garbage Matt

[nkchokshi]

Hay All, I need help, I am currently learning Nuke, Already working in Fusion.

I have tried to Use Garbage matte, in Nuke, but didn't find any option to add mask.
so i tried to use the roto node, but it didnt worked.

I have attached few screenshots, its getting confusing.
It was easy, in fusion i can just use the Bitmap Node to make black transparent.

The first image is output of Keyer

The second one is i added the roto node, and gives this output, i tried to invert the mask but it not working.

And this is how it looks.

So please help me to understand this .

[sathees]

change merge operation mode to "mask" to get what you want. No need to connect your roto node to your input.

[dcompz]

Or just hook the Rotopaint directly up to your Keyer, change the output to 'none', and set the premultiply to 'rgba' or just alpha.

Or hook it up, set it to invert, and change the color to black (0).