Attempting to set transparency in an imported bmp image

Question

Looking at a previous response to a similar question to this, I developed this code:

public static BufferedImage getImage(String imagefile) {

 BufferedImage image = null;

 try {

  image = javax.imageio.ImageIO.read(new java.io.File(imagefile)); 

  int trans = image.getRGB(0,0);
  final int width = image.getWidth();
  int[] imgData = new int[width];

  for (int y = 0; y < image.getHeight(); y++) {
   // fetch a line of data from each image
   image.getRGB(0, y, width, 1, imgData, 0, 1);

   for (int x = 0; x < width; x++)
    if (imgData[x] == trans)
     imgData[x] |= 0xFF000000;

   // replace the data
   image.setRGB(0, y, width, 1, imgData, 0, 1);
  }   

 } catch (Exception e) {

   e.printStackTrace();

 }

 return image;

}

In it, the idea is to take the upper left hand color and apply transparency on all pixels that matches that color in the image. The problem is when I do

g.drawImage(img, across, down, cells, cells, null);

I still get the color that is suppose to be transparent. Am I forgetting a step somewhere?

I used a bmp file to do the test.

Thank you for your time.

Answer 1

When I use alpha values in a BufferedImage I create the image using:

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

So maybe you need to copy/convert all the pixels to an image that is aware of the alpha values?

Answer 2

Got it:

public static BufferedImage getImage(String imagefile) {

 BufferedImage image = null;
 BufferedImage image_copy = null;

 try {

  image = javax.imageio.ImageIO.read(new java.io.File(imagefile)); 
  image_copy = new BufferedImage(image.getWidth(), image.getHeight(), BufferedImage.TYPE_INT_ARGB);

  int trans = image.getRGB(0,0);
  final int width = image.getWidth();
  int[] imgData = new int[width];

  for (int y = 0; y < image.getHeight(); y++) {
   // fetch a line of data from each image
   image.getRGB(0, y, width, 1, imgData, 0, 1);

   for (int x = 0; x < width; x++)
    if (imgData[x] == trans)
     imgData[x] &= 0x00FFFFFF;

   // replace the data
   image_copy.setRGB(0, y, width, 1, imgData, 0, 1);
  }   

 } catch (Exception e) {

   e.printStackTrace();

 }

 return image_copy;

}

Thanks for the help!

Looks like it was a logical error.