Blending two textures with a mask

[wima]

Hello

I want to blend two textures with a custom

mask. I have a mask, for example a black & white mask (also a texture) and

two other textures. At the white pixels of the mask I want to see texture one and at the black pixels of the mask I want the texture 2. I think this is the formula:

out = texture1 * mask + texture2 * (1 - mask)

I tryed with the Lerp operation but it does not work.

 

Thank you for help

wima