Best approach to transparent a noisy/brush image

Question

I'm using Photoshop CS6 (portable) to work in some image conversions. Sometimes, complex scenarios (for me anyway) like this one appear:

So, my goal is to transparent all dark blue parts and leave only white and white to transparent pixels on that image (maybe even some light gray ones too, if only white pixels are "impossible" to achieve). The area I need doesn't has a great resolution and it even contains some small artifacts and inconsistencies on it, but this was the best reference image I got, plus I must stick with this resolution...

My last attempt was to use the "Blend if" feature present on the "Layer Styles" window. Even so, it's been hard for me to adjust the settings in a way that doesn't ruin the image aspect I aim to keep. Either the scratched area gets too dense, either it gets too degraded, so I decided to ask if somebody here can provide me additional/different tips. I'm not a experience 2D designer, so any help could be useful...

Answer 1

If there really is nothing else than those white, partially not so opaque brush strokes mixed to an uniform dark background, the case is elementary.

I do not have Photoshop. This is in Affinity Photo, but it's the same in Photoshop. And this works as well in GIMP or Krita.

The original is still as a spare in the bottom layer, but it's not any more visible.

There's a red-green test layer and above it I have a white layer. The white layer has got your original as the layer mask. It's contrast is increased with curves to make the dark areas full black and the lightest areas to full white. The mask determines the transparency of the solid white fill color.

The fill color can be changed easily with the paint bucket. It's now blue:

If you had also something differently colored in the same layer as your brush strokes+the dark background, this would be useless. A totally different approach would be needed.