Just toying with single image fake HDR using contrast mask (luma invert overlay) and re-introduced details via a convolution technique that I’ve been experimenting with (under GEGL, smooth by domain set to Grain Extract then merged down for the convolution layer and setting that result to Grain Merge to introduce the details). Could use some more retouching, but keeping it simple (12:26am not to mention I’m tired and rusty as well as have to get to work in the morning; lol). 
