allow transparent background

[mastef]

Currently transparent source files will produce a black background.

[cancerberoSgx]

Hi, I can't reproduce it with a png source image in node.js and the browser. Can you provide some repro steps?, how are consuming the API ? JavaScript ? How are you loading the Bitmap passed to ImageRunner ?

That last part is important, make sure your library/technology supports alpha channel.

Also if you are doing something similar to geometrize-haxe-web I suggest trying removing those lines adding a first big background rectangle, I'm pretty sure Util.getAverageImageColor is full opacity.

Good luck