To help us understand the difference between destructive and non-destructive editing, we did the task twice, once destructively and once non-destructively.
First of all, we used the magic wand selection tool to select the sky area and then erased it by pressing Ctrl + Backspace. Then we created a new layer and added a gradient to it.
Destructive editing is bad because you are erasing the pixels and once they are gone they cannot be restored. Also, with the skyline, once you have destroyed the sky it is difficult to refine it if there is an area where the selection is wrong.
First of all, we applied a mask to our original image.
A mask is black and white information which tells photoshop what parts to hide in a layer – keeping the pixel information rather than deleting it as with Destructive editing. We then used the Refine Edge tool to perfect the edges of the mask to make sure there was no colour bleeding from the sky. Finally, we added the gradient to a lower layer.