03 Selection edges
But if I zoom in to an area on the horizon at the far left of the picture, you can see the problem with Freehand Lasso selections. I haven’t followed the outline of the rocks accurately, so you can see a sharp division between the adjusted and unadjusted areas of the picture.
I’m not going to try to make a more accurate selection. Instead, I’m simply going to blend in the one I’ve got more smoothly.
04 Gaussian Blur filter
And the way to do this is to first select the layer mask by clicking on its thumbnail, then use the Filter > Blur > Gaussian Blur menu option. In the Gaussian Blur dialog, drag the Radius slider to the right – you’ll see the edge of the selection blurring as you do this. By the time I get to a radius of 30 pixels, the selection edge has smoothed over so much you can’t really see it any more. This does mean the adjustment ‘bleeds’ into surrounding areas, but this rarely matters. The trick is to increase the radius just enough to hide the edge, but then stop.
05 Darkening the bottom corner
I’ve made another Freehand Lasso selection in the bottom right corner where I want to darken the rock pavement, but I haven’t gone right up to the diagonal line of rocks in the centre, because I want to produce a light-to-dark shading effect. Next, I created a new Levels adjustment layer, then reduced the brightness. There’s a really obvious edge, but I’m not worried about that…