At a recent Photoshop users group we talked about brightening the teeth in a portrait that was taken. I will never say I am a good portrait photographer (this is an image I took at NECCC in 2005 which has a number of problems but does have teeth), but I can review how we used layers and a layer mask to accomplish this.
I will start off by saying that I talk to my self a lot while working with Photoshop. I will say out loud what I am trying to do. So I start here by saying that I would like to have the teeth brighter and just have the bright teeth show from another layer. Also being lazy (and to help reduce the chance for errors) I will create the lighter layer below the layer that I will use for the rest of the face. I always like to leave my original image alone so I will create two copies of my background layer and name them.
Notice that I named the layer above the background layer white teeth, and the top layer is called final face. This will help me keep it straight in my mind what I want to do with each layer. So next I will turn the eye off on the final face layer so I can see what I am doing on the layer below it and select the white teeth layer to work with. You can use Brightness/Contrast or Levels from “Image>Adjustments” and in this case I chose Levels. I changed the white point to make the teeth brighter.
Now that I have bright teeth I turn the eye on for my final face layer and select that layer. On the bottom of the layers palette I chose the layer mask icon to create a layer mask for the final face layer, and make sure that the mask is selected to be active. I zoom in on the mouth so the teeth fill most of the frame. No to actually mask something I make my foreground color black and choose the brush tool. I adjust the size of the brush to be small compared to the size of the teeth and paint over the teeth (remember we are painting onto the layer mask, and not the image for the layer).
Someone asked me how to do you see what you have for a make? An easy way to see that you are masking is to turn off the background and bright teeth layers. You will get something like the following image and you can see that I have only painted a mask for the teeth.
Now in the last image you can see the difference between the original image and the one where we have brightened the teeth.