[android-developers] question about blending bitmaps (Porterduff? matrix?)

I'm looking for the best way to combine/blend two (or more) solid-color
bitmap so the colors are combined. The bitmaps have one color with an
alpha value of 102 for solid color bitmaps, 102 and decreasing to 0 at
about 48% of the bitmap's height (from either the top or bottom) for
graduated color bitmaps, and for split-field, the same, except not a
gradual change---just 102 then 0 at 50%.

By blending, what I mean is this: Imagine that you have two sheets
of colored plastic. You look through one of them, and you see its
color over the scene behind it. You then add the second sheet of
a different color clear plastic, and now you see the two colors
interacting to make a new color. That is what I'm trying to do.

In the case of graduated or split-field, the transparent area should
not interfere with a second filter's color where it is colored in
the transparent area of another.

Btw, all of these bitmaps are created as needed using
Bitmap.createBitmap (ARGB_8888), paint, and drawing on the canvas.
I was using 60x40 png files for the solid colors, but the transparent
white background ended up not being so transparent.... Now I just
create larger bitmaps with NO background---just color (alpha 102) or
completely transparent.

What would be the best way to do this? If Porterduff, which mode?
Or would some type of matrix calculation be better? Or is there
another way that I haven't come across yet?

(If the best way calls for a matrix, a pointer to a good matrix tutorial
would be really helpful.)

Thanks,
--jim

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