For contrast masking in
PS, check
here.
Duplicate layer.
Desaturate: Colors>colorize>Hue, 0; Saturation, 0
Invert: Colors>Negative image
Gaussian blur: Effects>Blur>Gaussian (r>5)
Set blend mode to overlay
Reduce opacity of layer if necessary
Changing the blend mode to overlay before blurring allows you to see the effect of changing the radius.