How to save a 32bit tif file.
-Create a new layer (this layer should be transparent)
-Paint image on layer
NOTE: “layer mask from transparency” will not work, it must be a standard channel.
-Right click on layer in layer palette, select "Select Layer Transparency"
-Under select menu, select "Save Selection"
- or on channel palette, select "Save Selection as Channel" button.
-Name the channel what ever you want ("alpha" helps organize things)
NOTE: the first (nonRGB) channel will be the alpha in the tiff.
-Select "Save As" under the file menu.
-IMPORTANT, select the tif file type and CHECK THE SAVE ALPHA BOX under the file type pull down list.
-Use any method you like to paint the image.
-Select the area that will be the alpha channel.
-Now do all the steps in method 1 beginning at the 4th step.