How to create a variable-opacity mask (by adjusting a slider)

[Guy Burns]

I am contrast-correcting B&W negatives from the 1950s that are seriously overexposed. If they weren't of historic interest to Tasmanian bushwalkers, I'd be binning them. As it is, I'm trying to correct them.

The overexposure, after an initial correction with a Curves 1 layer (for maximum contrast) and then a Curves 2 layer (for overall contrast) renders the shadows to solid black. I correct the blacks by selecting them (from a layer above), so that I select just those levels that have been rendered black. I feather by a certain amount, and with the selection still active, I create a Hide Selection layer mask for Curves 2. The result is that the black area is now at the original overexposed level and looks out of place. Filling the mask with a shade of gray alters the amount that the shadows are darkened to try and match the surrounds.

The method works well enough for the poor images, but it is time consuming because I have to run through the fill process several times before I achieve a suitable effect. What I'd like is to be able to adjust the opacity of the mask with some kind of slider so that I can quickly choose a suitable value for the density of the mask.

Anyone know how to do that?

A sample file can be downloaded here. Note there are several other adjustment layers not in play for this image.

[c.pfaffenbichler · Accepted solution]

Have you tried »Density« in the Properties Panel? 

Edit: The old-school approach would be a Shallow Knock Out-Layer Clipping Masked to the Adjustment Layer. 

[c.pfaffenbichler · Accepted solution]

And might a slightly less steep and subsequently clipped Curve not also suffice? 

Anyway here are screenshots to illustrate the Density. 

The Properties Panel can also be used to edit a Mask’s Feather. 

[Guy Burns]

You're a clever fellow – you answered a question I didn't even ask. Now I can adjust the density and the feathering at the same time. Just what I've been looking for!

Re the less steep curve. Very much a matter of taste and me trying to reflect the lighting conditions at the time. Looks like the sky was heavy with cloud above, but there are breaks in the sky above the mountains. The sun was behind the photographer. Those dark areas at the bottom of the range: different vegetation or cloud shadow? I've just been to the area (Lake Pedder, now flooded by a hydro electric dam) to mimic some of these photos from 70 years ago, so I know the dark areas are caused by cloud shadows. That's why I had a very steep curve to increase the contrast and deepen those shadows – but the foreground bush was thrown completely black.

Now I have yet another method to correct for a common problem in these negatives: lack of contrast, and correcting for that gives lots of ugly blacks.

Thanks again. I'll incorporate this technique into my Action.

[c.pfaffenbichler]

You’re welcome. 

As concerns the Feathering: Try to keep in mind that if you scale the Layer the Feathering value will not scale along with it and may need to be corrected manually.