Attached Link: Holiday Blues

DId you manage it, Frank? Hard to find things on G@P nowadays - so many goodies:)

I used the method in some of my images - see link for example, the flying objects are an eco inside a transparent cylinder.

However, except for cylinders and cubes it doesnt work very well. If you look at the cone and sphere you can see that it fills the object, but it continues below the bottom of the object. The reason for that is that eco instances are put on the surface of the object as though droped from above, along the z axis. So if you populate a sphere normally it will only populate the top half. It knows nothing about the bottom half. using this method it just makes the instances populate a slab directly underneath the surface. So, for exampe, any instance that would have hit the sphere on the equator will be droped in a straight line (along z) , but that would be outside the sphere...
I couldnt come up with a method to overcome this easily. I tried a boolean intersection with another sphere of the same size, but it ignores the eco. I think if you convert the eco instances to objects, group them, do the intersection with the sphere and return them to the eco it may work. Depending on the number of instances this may or may not be practical.

If anyone else comes up with a solution  - please post, I had other images In which I wanted to use it and couldnt becuase of this problem. (eg populate the inside of a character with things...)
PS My filter in the function editor is slightly different from  what was suggested by G@P - they use two filter one to multiply (aX) and one to offset (X+a). I used the contrast/brightness which doesnt actually need to be applied to contrast or brightnest, it performs aX+b which is the same as the multiply and offset put together.

"I paint that which comes from the imagination or from dreams, or from an unconscious drive. I photograph the things that I do not wish to paint, the things which already have an existence."
Man Ray, modernist painter
http://artpearl.redbubble.com/