Learn a quick and easy way to separate an image from its background when one is lighter than the other, as shown below:
Open the image you want to use. I chose the image below because I couldn’t easily select the flower petals easily with any other tools.
Go to the channel menu which is right next to the layers palette.
Deselect the RGB opacity eye. Then mess around with the other view (There should only be one eye left each time) until you find the view with he most contrast the one that looks the best.With my picture the Red channel looked best, but it will be different in every picture.Drag the channel you have chosen to the (create a new channel) icon. It looks like this ()Once you have a new channel select it and go to Image > Adjustments > Levels. The settings of the sliders will vary from image to image, but basically you want to make a lot of contrast between what you want out of your picture and the background. Hear is what I had at this point.
The next step is to fill in some of the black spaces with a brush. Once that is done do the same thing with some of the white spaces.
Next make all the channels visible. Go to the layer menu and click on the image layer. Then press Ctrl + Alt + 4. That should select the background of the image. Just go to Edit > Clear to make it go away and you can paste in a new background for your image.My final result looks cheesy, but you can see with a little bit of time you could really get some cool effects using channels.