How to change the brightness of an Image

Question

My Question: I want to be able to change the brightness of a resource image and have three instances of it as ImageIcons. One at 50% brightness (so darker), another at 75% brightness (a little brighter), and finally another at 100% brightness (the same as the original image). I also want to preserve transparency.

What I've tried: I've searched around and it looks like the best solution is using RescaleOp, but I just can't figure it out. I don't know what the scaleFactor and the offset is all about. Here's my code for what I've tried.

public void initialize(String imageLocation, float regularBrightness, float focusedBrightness, float pressedBrightness, String borderTitle) throws IOException {
  BufferedImage bufferedImage = ImageIO.read(ButtonIcon.class.getResource(imageLocation));
  setRegularIcon(getAlteredImageIcon(bufferedImage, regularBrightness));
  setFocusedIcon(getAlteredImageIcon(bufferedImage, focusedBrightness));
  setPressedIcon(getAlteredImageIcon(bufferedImage, pressedBrightness));
  setTitle(borderTitle);
  init();
}

private ImageIcon getAlteredImageIcon(BufferedImage bufferedImage, float brightness) {
  RescaleOp rescaleOp = new RescaleOp(brightness, 0, null);
  return new ImageIcon(rescaleOp.filter(bufferedImage, null));
}

The call would be something like this:

seeATemplateButton.initialize("/resources/templateIcon-regular.png", 100f, 75f, 50f, "See A Template");
//I think my 100f, 75f, 50f variables need to change, but whenever I change them it behaves unexpectedly (changes colors and stuff).

What happens with that code: The image appears "invisible" I know it's there because it's on a JLabel with a mouse clicked event on it and that works just fine. If I just skip the brightness changing part and say setRegularIcon(new ImageIcon(Button.class.getResource(imageLocation)); it works just fine, but obviously it's not any darker.

What I think I need: Some help understanding what offset, scaleFactor, and the filter method mean/do, and consequently what numbers to give for the brightness variable.

Any help would be greatly appreciated! Thanks!

Answer 1

The doc says:

The pseudo code for the rescaling operation is as follows:

for each pixel from Source object {
    for each band/component of the pixel {
        dstElement = (srcElement*scaleFactor) + offset
    }
}

It's just a linear transformation on every pixel. The parameters for that transformation are scaleFactor and offset. If you want 100% brightness, this transform must be an identity, i.e. dstElement = srcElement. Setting scaleFactor = 1 and offset = 0 does the trick.

Now suppose you want to make the image darker, at 75% brightness like you say. That amounts to multiplying the pixel values by 0.75. You want: dstElement = 0.75 * srcElement. So setting scaleFactor = 0.75 and offset = 0 should do the trick. The problem with your values is that they go from 0 to 100, you need to use values between 0 and 1.