Dalton Filho

A while ago I was working on a new feature of a CG project that involved loading hundreds of textures from disk. So far, so good. The images, however, were like an order from the devil: I needed RGBA images, but the images were all in BMP format (no chance for alpha channels) and splitted. How great is that?! To solve this problem, I had two alternatives: the first was joining and converting the images manually. If you consider the ammount of images (422) and the average time to join and convert them (aprox. 3 minutes), that would take more than 21 hours (assuming the bore factor wouldn’t spoil my productivity in the meanwhile). Fortunately, there was a second alternative: automating the whole process. As I could not find a program that could supply my very specific need, I knew I had to make a little program for that, and there came JAI for the rescue. I took almost an hour googling, reading API docs and trying different commands until I found the ones I needed to create an alpha channel from a color and saving the image to PNG format as below:

    /**
     * Reads an image from disk and exports it to PNG format using 
     * alphaColor as the transparent color.
     *
     * @param alphaColor the color to use as the trasparent color
     * @param src the path of the source image
     * @param dst the destination path of the exported image
     */
    void toPNG(Color alphaColor, String src, String dst) {
        RenderedImage image = JAI.create(”fileload”, src);

        PNGEncodeParam.RGB param = new PNGEncodeParam.RGB();

        param.setTransparentRGB(new int[]{alphaColor.getRed(),
                                          alphaColor.getGreen(),
                                          alphaColor.getBlue()});

        JAI.create(”filestore”, image, dst, “PNG”, param);
    }

The resize code:

    /**
     * Reads an image from the given src and writes it to the
     * given dst resized to the given width and
     * height.
     *
     * @param src the path of the source image
     * @param dst the destination path of the exported image
     * @param width the width of the new image
     * @param height the height of the new image
     */
    void writeResizedPNGImage(String src, String dst, int width,
                              int height) {

        RenderedImage image = JAI.create(”fileload”, src);

        BufferedImage buf = new BufferedImage(width, height, BufferedImage
                                             .TYPE_INT_ARGB);

        Graphics2D g = buf.createGraphics();

        AffineTransform transform = new AffineTransform();

        // Resize to fit
        transform.setToScale(width / (double) image.getWidth(),
                             height / (double) image.getHeight());

        g.drawRenderedImage(image, transform);

        JAI.create(”filestore”, buf, dst, “PNG”);
    }

Useful links: JAI download. JAI API docs.