How Can I Create an PNG with Alpha Transparency

[slevytam]

Hi,

I was wondering if someone could help me create a PNG that when overlayed on an image only shows when its on top of black.

ie the image underneath is black and in some spots there is color. Wherever there is black I would like the overlayed png to show. Wherever there is color I would like to the overlayed png to be transparent.

Really appreciate any help,

Thanks

slevytam

NOTE***: The closest ive got is making a layer of the photo then adding a layer mask which is the exact same photo.