ABSTRACT
Open Chapter 16/TropicalMartini.tif, which has a layer of a tropical scene, and a layer for a green drink. The drink does not appear to belong in this scenery, because you cannot see through the glass. You could take the master opacity down of the entire layer, but then you would see through the cherry. The martini glass itself contains the information we need for the mask. We will use one of the RGB
channels of the martini for our layer mask. Hit Ctrl 1 [Command 1] to see the red channel of the document. Turn visibility off for the “Tropical Scene” layer to see the martini glass only. The red channel could be a good candidate, but the cherry and drink gray values are nearly the same color. We need a channel that has an edge for the cherry so we can make it opaque, and the drink semi-opaque. Don’t worry about having the exact gray value for the green drink, as we have curves that can adjust that later. Hit Ctrl 2 [Command 2] to solo the green channel; this looks better as the cherry has a contrasting edge with the drink. The details of the glass rim and the shadow at the top of the green drink are preserved. Ctrl A [Command A], Ctrl C [Command C] to select all and copy the red channel data as gray values to the clipboard. Make a new layer mask for the Martini layer, by clicking on the add layer mask icon while the Martini layer is active in the layers palette. Alt [Option] click the layer mask for the martini layer and Ctrl V [Command V] to force paste the data into the layer mask. This will not work if you just select the layer mask, you must see the layer mask to paste into it. Click on the Martini layer thumbnail, to show your results. Very good, except the data is not centered, so we will nudge it into place. Usually this will center, but this layer is missing the pixels outside of the martini. With the selection edges still active, click on the layer mask, to make that the target of the nudging. Use the cursor keys to nudge it into place and Ctrl + [Command +] to zoom into a 100% view to be more accurate. Keep your eyes on the cherry stem, as it is a good candidate for registering the mask.
