03 Drag out the gradient
Now I click near the top of the sky where I want the mask to be at its strongest, then drag downwards to fade it out towards the horizon. If you hold down the shift key as you do this, it ‘constrains’ the gradient to a vertical line.
04 Show or hide the mask
The mask is shown here as a red overlay over the image. You can use the same menu shown in step 2 to choose whether the mask is displayed all the time (not very helpful) or only when you’re adjusting it (more useful).
05 Make your adjustments
That’s the option I’ve chosen here, because the mask disappears as soon as I start modifying my ‘Sky grad’ adjustment layer, making it easier to see the effect. I’ve reduced the Exposure value and bumped up the Contrast to make the sky a darker, richer blue – and because I’ve used a gradient mask, the darkening effect fades out before it starts to overlap the top of the car.