For this image, I have changed the sky.
To do this, I chose the channel that had the best contrast between black and white, which was the green channel. I then copied this channel.
I used the dodge tool to colour in the background white. The good thing about the dodge tool is that I could go over the flag and it wouldn't make it white. I then used the burn tool on the flag to make it black.
I then clicked on the RGB channel bar and went back onto layers as I needed to make the image active. I then inversed the image and added a mask.
I then chose an image of the sky that I wanted to use on this image. I dragged the sky image onto the flag image and placed the sky where I wanted it to go. I then clicked the tick at the top. Then in the layers palate I moved the layer underneath the background copy.
Lastly, I changed levels to balance the two images together.
