This week's book giveaway is in the OCAJP forum. We're giving away four copies of OCA Java SE 8 Programmer I Study Guide 1Z0-808 and have Jeanne Boyarsky & Scott Selikoff on-line! See this thread for details.
Create a BufferedImage with the same size. Paint the original image on the BufferedImage. Then, go through all pixels of the BufferedImage using getWidth(), getHeight() and getRGB(), and reset the pixel using setRGB if it's a white pixel.