Wanna know how to turn this:



Into this:



First, take your picture, obviously(!), and create a new raster layer by going to Layers >> New Raster Layer
Fill that layer with a color similiar to this and set to 'soft light':



Now create another raster and fill it with a gradient like this and set to 'lighten':



To do this go to the gradient properties by clicking here in the materials window:



Now you need to select the gradient tab. You can select a premade gradient or make your own. To make your own you need to click Edit >> New... then call it whatever you like (i've called mine blackpurple)

Then click the little marker highlighted in red below and then the color box at the side to select the color you want (in this case black).



Repeat this process but clicking the opposite marker first to change the other color of the gradient. The final gradient should look like this:



When you have filled your raster layer with the gradient you have created, set it to Lighten.
Now duplicate the base and drag it to the top layer. Set the opacity to a number around 50 in the Layer Palette like this:



Now to finish the picture off with a softer look go back to your bottom layer which is the orignal picture. Go to Adjust >> Blur >> Gaussian Blur and set it to 0.50 and it will make the overall picture look much softer.

The end.