Knocking Out Using Channels
Our first example (and my favorite cuz it takes nothing more than Photoshop and some knowledge) of knocking out Hedda uses channels. Most people have seen the channels roll-out and few people use them. We'll be creating new channels and using them as masks.

Here's Hedda, posed against our green screen. In working with this photo, I realized that I should have had more light at the top of Hedda's head. Remember, flat lighting is the key. We'll go ahead and work with this image to show that the techniques can be used on less than perfect images.

Do a CTRL-A to copy all and a CTRL-V to past the image onto a new layer. Turn off the background layer.



Click on the circle at the bottom of the layers pallette and choose 'Channel Mixer' as shown.

The Channel Mixer control panel that pops up has a check box for 'Monochrome' at the bottom . We are trying to achieve maximum contrast between the background and the subject. Adjust the sliders, trying to make the foreground black and the background as light as possible without losing the details. Watch the hair in the bottom left corner in our example as we go through this tut. It doesn't have to be perfect, we'll work on it more in coming steps.

Repeat the steps above to create another Channel Mixer layer, this time, use different settings to try and keep the highlights in the hair. don't worry about the subject proper, just concentrate on the edges. Try to get as much contrast between the two areas as you can.