Masks in Photoshop keeps part of an image safe, when i created a mask on part of an image is protected when i began editing the image. The red overlay on this image is a quick mask, this enables me to make changes only to the visible are of the image. I painted over the statue to protect it from being edited with the rest of the image.
When I have selected the channel Photoshop will show a black and white version of the image this hides all of the colour channels.
With a background ready i began looking at each channel in the image, this enabled me to pick a channel that gave me the most contrast for the mask i created.
Cyan was the channel that gave me most contrast I began to adjust the copy.
Here is the contrast you get with Cyan.
This allowed me to see the background through the area that is black with some editing, after adding some paper to the top and bottom of the image i had the makings of a book cover I added text to the top and created a Zen Garden book cover.