Is there any simple way to extract the "baked in" transparency in a layer and turn it into a layer mask in Photoshop? To take a simple example: Let's say that I paint a few strokes with a semi-transparent brush, or paste in a .png-file with an alpha channel. The rgb color values and the alpha value for each pixel are now all contained in the layer-image itself. I would like to be able to edit the alpha values as a layer mask, so that the layer image is solid and contains only the RGB values for each pixel.

Is this possible, and in that case how? Thanks.

EDIT: To clarify - I'm not really after the transparency values in themselves, but in the separation of rgb values and alpha values. That means that the layer must become a solid, opaque image with a mask.