Adobe Tutorial- Masking with channels

Before Image

Open you image, and go to the Channels panel and toggle through the different channels to find the most contrast between the subject and the background. With the channel selected go up to Image > Calculations. It makes a brand new channel that makes the background even darker than it is before, creating a better contrast. Press Command I to invert the image. Press shift/delete which brings up the fill menu. In Use menu select black. And set the blending section to overlay. And select okay. Grab brush tool and use a small brush and change the blend mode to overlay. Then color in the image that you want to keep with black. Then invert it back so the selected area will be white. Then go back into your RGB channel and turn it back on. Go to your layers panel and unlock the background layer. Go to select menu and go to load selection and load the Alpha 1 channel you created. Load it as a new selection and press okay. Click the layer mask icon in the layers panel, and put a new layer underneath that layer and give it a different color background to make it stand out.

After Image

Sources: The Tutorial came from Layers Magazine.com and the image is from my personal pictures on my computer.