A Script that can convert White to Transparency, as good as such a thing can be.

WhiteToTransparent.java

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

import javax.imageio.ImageIO;

public class WhiteToTransparent {
	public static void main(String[] args) {
		if (args.length < 2) {
			System.out.println("usage: java WhiteToTransparent <sourceFile>.png <destFile>.png -i");
			System.out.println("-i: inverted");
			System.exit(2);
		}
		boolean inverted = (args.length > 2 && args[2].equals("-i")) ? true : false;
		File source = new File(args[0]);
		File dest = new File(args[1]);
		if (dest.exists()) {
			dest.delete();
		}
		if (!source.exists()) {
			System.out.println(source + " could not be found! exiting.");
			System.exit(3);
		}
		try {
			int alpha = 0;
			BufferedImage bim = ImageIO.read(source);
			for (int x = 0; x < bim.getWidth(); x++) {
				for (int y = 0; y < bim.getHeight(); y++) {
					Color c = new Color(bim.getRGB(x, y));
					if (inverted) alpha = ((c.getBlue() + c.getGreen() + c.getRed()) / 3);
					else alpha = 255 - ((c.getBlue() + c.getGreen() + c.getRed()) / 3);
					bim.getAlphaRaster().setSample(x, y, 0, alpha);
				}
			}
			ImageIO.write(bim, "png", dest);
			System.exit(0);
		} catch (IOException e) {
			e.printStackTrace();
			System.exit(1);
		}
	}
}