Discovered how to do it;
Using other Mask as example.
Select 8 various combinations of corners of texture you want Mask of in black with anti-aliasing each combo creating 256 X 256 selections.
stack the 8 textures resulting in 256 X 2048 image then convert to grey scale
re-size stack from 256 X 2048 to 32 X 2048 (should look like sample.
Next with Microsoft image tool load image and set format to Mask then create mips. Save file with file naming convention as in "world" "texture" folder ( ones with "M" in their file name.
John