Help! How to derive a mask from a "max" style blend node.

Tacocombo

I attached a quick example below. I'm struggling with how to derive a solid one-bit style mask from two heightfields blended using the max style blending.

My mockup below is basically approximating some pebbles I want to blend on some sand. But I can't use the original pebble generator as a mask because a lot of the pebbles get clipped below the sand. I need to find a way to build a mask of where the pebbles are after the blend, so I can control their coloring precisely later on.

Any help would be greatly appreciated.

p.s. I posted this at Allegorithmic's forums as well, in case anyone thinks this is familiar. I'm that desperate!

Raane

It might be a little clumsy but try using a difference blend between the perlin before and after dots. That should give you a reasonable basis.

Tacocombo

Excellent! That is exactly what I needed, thanks so much.

Raane

It is a bit of a clumsy method and doesn't work conclusively for all situations.

bugo

Use a divide and the histogram scan, tweak the values and ur gold

bugo

Here's how I'd do it.