Java – Image Manipulation

Handling Images in Java is fun. Here are some often used image manipulation methods.

Most of these methods come from my java heatmap creating class so if you want to download them get them there.

Negating colors of an image

    /**
     * returns a negated version of this image.
     *
     * @param img buffer to negate
     * @return negated buffer
     */

    private BufferedImage negateImage(BufferedImage img) {
        int width = img.getWidth();
        int height = img.getHeight();
        for (int x = 0; x < width; x++) {
            for (int y = 0; y < height; y++) {
            int rGB = img.getRGB(x, y);                 //Swaps values
            //i.e. 255, 255, 255 (white)
            //becomes 0, 0, 0 (black)
            int r = Math.abs(((rGB >>> 16) & 0xff) - 255);  // red inverted
                int g = Math.abs(((rGB >>> 8) & 0xff) - 255); // green inverted
                int b = Math.abs((rGB & 0xff) - 255); // blue inverted

                // transform back to pixel value and set it
                img.setRGB(x, y, (r << 16) | (g << 8) | b);
            }
        }        
        return img;
    }
UPDATE: a much faster way to negate the image (result differs a bit from version above, but generally it should not make much of a difference):
    private BufferedImage negateImage(BufferedImage img) {
        RescaleOp op = new RescaleOp(-1.0f, 255f, null);
        BufferedImage negative = op.filter(img, null);
        return negative;
    }

Change all pixels in BufferedImage to one color

    /**
     * changes all pixel in the buffer to the provided color.
     *
     * @param buff buffer
     * @param color color
     */

    private void paintInColor(BufferedImage buff, Color color) {
        Graphics2D g2 = buff.createGraphics();
        g2.setColor(color);
        g2.fillRect(0, 0, buff.getWidth(), buff.getHeight());
        g2.dispose();
    }

Changing opacity of image

    /**
     * changes the opacity of the image.
     *
     * @param buff1 buffer to change opacity
     * @param opaque new opacity
     */

    private void makeTransparent(BufferedImage buff1, float opaque) {
        Graphics2D g2d = buff1.createGraphics();
        g2d.setComposite(
                AlphaComposite.getInstance(AlphaComposite.SRC, opaque));
        g2d.drawImage(buff1, 0, 0, null);
        g2d.dispose();
    }

Adding two BufferedImages (with given opacity)

    /**
     * prints the contents of buff2 on buff1 with the given opaque value
     * starting at position 0, 0.
     *
     * @param buff1 buffer
     * @param buff2 buffer to add to buff1
     * @param opaque opacity
     */

    private void addImage(
            BufferedImage buff1, BufferedImage buff2, float opaque) {
        addImage(buff1, buff2, opaque, 0, 0);
    }

    /**
     * prints the contents of buff2 on buff1 with the given opaque value.
     *
     * @param buff1 buffer
     * @param buff2 buffer
     * @param opaque how opaque the second buffer should be drawn
     * @param x x position where the second buffer should be drawn
     * @param y y position where the second buffer should be drawn
     */

    private void addImage(BufferedImage buff1, BufferedImage buff2,
            float opaque, int x, int y) {
        Graphics2D g2d = buff1.createGraphics();
        g2d.setComposite(
                AlphaComposite.getInstance(AlphaComposite.SRC_OVER, opaque));
        g2d.drawImage(buff2, x, y, null);
        g2d.dispose();
    }

Saving BufferedImage to a file

    /**
     * writes the image in the provided buffer to the destination file.
     *
     * @param buff buffer to be saved
     * @param dest destination to save at
     */

    private void saveImage(BufferedImage buff, String dest) {
        try {
            File outputfile = new File(dest);
            ImageIO.write(buff, "png", outputfile);
        } catch (IOException e) {
            print("error saving the image: " + dest + ": " + e);
        }
    }

Loading a BufferedImage from a file

    /**
     * returns a BufferedImage from the Image provided.
     *
     * @param ref path to image
     * @return loaded image
     */

    private BufferedImage loadImage(String ref) {
        BufferedImage b1 = null;
        try {
            b1 = ImageIO.read(new File(ref));
        } catch (IOException e) {
            System.out.println("error loading the image: " + ref + " : " + e);
        }
        return b1;
    }

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