Look Development: Fixing Black Patches

I looked at a number of tests to see if the alpha in the black patches was being calculated correctly.  First, I used the same alpha channel and set the image into a red background instead of black. 

As you can see from the image, the alpha extends outward too far, thus we get particles with partial opacity in areas we need to see through. 

From here, I tried to reset the opacities of particles that were darker in the expression editor.

No fix on black particles.

Clamping particles with RGB < (.3, .3, .3)

Clamping particle with RGB < (.4, .4, .4)

With transparency expressions.

This works a little bit, but it could start eating away at particles I want to keep if I'm not careful.  Plus, there still seem to be some dark particles muddying up the transparent sections that I can't seem to get rid of.  You can see this below with the green background.

Muddy particles... :-P.

So my next step was to adjust the levels of the original alpha layer, basically creating a much smaller falloff around the opaque areas, kind of like a erode function.  This seems to be the best solution.

With no transparency expression.

With transparency expressions.

With size variation.