Here it is again, but this time a little differently.
Duplicate your image. Add layer mask to top layer. Add gradient to top layer. This time I went from right to left.
Click on the bottom layer. Open Levels tool. Adjust the levels slider(same one) until it looks right.
This time I went to the dark side!
Now you can either merge down(after clicking the top layer) or do new from visible. Again, good luck!