png alpha bug.

I render a bunch of small png images that needed to keep alpha values specific. The render window show them to be exactly correct, but after saving them and checking again, many pixles that were 255 were down as low as 150. ( a 3ds user in this project had the same problem)
At first I suspected osa, but Iv’e eliminated that.
What could cause that ‘alpha blur’, and has anyone else had that problem.?

Do you have the “rgba” button pressed in the render buttons -> format panel? Do you have the “key” pressed in the render buttons -> render panel?


Thanks, but no luck.
That Key button sounded promising, but the alpha values through the center of the character still wander.(they were solid before saving.
I should mention that there is a halo emiter behind the character. Further test with just a cube (alpha 255) and packground (alpha 0) , again perfect in render window, again after saving, alpha values wandered near the edge.