adobe photoshop - Can I extract shadows from a texture to make a transparent image (png)?

I have this image:

And I would like to extract the dark parts (shadows) to make a transparency consisting of black pixels at different alpha channel values. Here is a crude example image of what I am trying to extract:

This way, if I put solid colors behind the image, that texture will show up over the new color and make it look nice and purdy.

I suppose another way I can ask this question is how I can turn a layer working with an "overlay" or "linear burn" blend option selected into a png consisting of black pixels at different alpha channel values.

Tough question to put in words, my apologies for any confusion.

Answer

Best bet is probably Select > Color Range. Then click a white portion of the canopy and play with the "Fuzziness" slider to get you where you want.

Once you do that click okay and your'e left with a selection. Make the selection a Mask (probably have to invert the mask afterwards). Then simply lower opacity for the layer and Save for Web.

You can save specific steps of various transparency....

20%

40%

60%

80%

100%