It appeared that the masking layer (inverted image) looked like an alpha channel. Just opposite of Xara when an image is used for transparency.

I made a new layer and filled it with black. With the masking layer, this gave a black image with the transparency with respect to the gray image. The original image would be transparent, but gray itself.

An optimized PNG seemed to me that it would have something similar to a binary alpha channel. The transparency would be full transparent or full opacity.

I am still trying to learn how to do this and make sense of things. I can only my old computer in the day light due to severe black and white problems at nignt. Skunks.

Rich