Java – Making a Certain Color on a BufferedImage Become Transparent

java

A very similar question that has been answered: How to make a color transparent in a BufferedImage and save as PNG

Unfortunately I couldn't formulate an answer for myself out of that source.

Q: I draw a BufferedImage to my Canvas and would simply like to create a method that turns every pixel with the a certain color (in this case: [214, 127, 255] / 0xD67FFF) into a transparent one. The BufferedImage is of type ARGB.

I do not want to save the BufferedImage as a file, simply display it on my canvas.

Thanks in advance.

Best Answer

Iterate over all the pixels and perform the check and make transparent.

for (int y = 0; y < image.getHeight(); ++y) {
    for (int x = 0; x < image.getWidth(); ++x) {
         int argb = image.getRGB(x, y);
         if ((argb & 0x00FFFFFF) == 0x00D67FFF)
         {
              image.setRGB(x, y, 0);
         }
    }
}

Make sure the BufferedImage uses an alpha channel, otherwise it will become black.
Note that this will affect your original image.

Edit: Note that I changed the check. Therefor it wouldn't have worked because of I assume your pixels were solid (alpha = 255).

(0xFFD67FFF & 0x00FFFFFF) will result in 0x00D67FFF
And, (0x00D67FFF == 0x00D67FFF)

Related Solutions

Java – How to assert that a certain exception is thrown in JUnit 4 tests

It depends on the JUnit version and what assert libraries you use.

For JUnit5 and 4.13 see answer https://stackoverflow.com/a/2935935/2986984
If you use assertJ or google-truth, see answer https://stackoverflow.com/a/41019785/2986984

The original answer for JUnit <= 4.12 was:

@Test(expected = IndexOutOfBoundsException.class)
public void testIndexOutOfBoundsException() {

    ArrayList emptyList = new ArrayList();
    Object o = emptyList.get(0);

}

Though answer https://stackoverflow.com/a/31826781/2986984 has more options for JUnit <= 4.12.

Reference :

JUnit Test-FAQ

Java – How to make a color transparent in a BufferedImage and save as PNG

I did that recently, to answer a question of my project manager.
The function transforming gray to transparency is:

  private Image TransformGrayToTransparency(BufferedImage image)
  {
    ImageFilter filter = new RGBImageFilter()
    {
      public final int filterRGB(int x, int y, int rgb)
      {
        return (rgb << 8) & 0xFF000000;
      }
    };

    ImageProducer ip = new FilteredImageSource(image.getSource(), filter);
    return Toolkit.getDefaultToolkit().createImage(ip);
  }

Actually, it acts on a gray-level image, so I just copy a RGB component (the R one) to alpha, discarding the others which are identical in my case.
You can adapt it to filter a specific color, eg. with a test of equality or range, etc.
Of course, the BufferedImage must be of BufferedImage.TYPE_INT_ARGB type.

I don't address the question of saving, as it is pretty trivial, but I can add this code page too.

[EDIT] To convert Image to BufferedImage:

BufferedImage dest = new BufferedImage(
    imageWidth, imageHeight,
    BufferedImage.TYPE_INT_ARGB);
Graphics2D g2 = dest.createGraphics();
g2.drawImage(image, 0, 0, null);
g2.dispose();

[EDIT 2] I come after Christoffer posted his complete solution, but here is mine, I show how to make a range of colors transparent. Can be improved, eg. using HSB components instead.

import java.awt.*;
import java.awt.image.BufferedImage;
import java.awt.image.FilteredImageSource;
import java.awt.image.ImageFilter;
import java.awt.image.ImageProducer;
import java.awt.image.RGBImageFilter;
import java.io.*;

import javax.imageio.ImageIO;

public class AddTransparency
{
  AddTransparency() throws IOException
  {
    String imagePath = "E:/Documents/images/";
    File inFile = new File(imagePath, "map.png");
    BufferedImage image = ImageIO.read(inFile);

    Image transpImg1 = TransformGrayToTransparency(image);
    BufferedImage resultImage1 = ImageToBufferedImage(transpImg1, image.getWidth(), image.getHeight());

    File outFile1 = new File(imagePath, "map_with_transparency1.png");
    ImageIO.write(resultImage1, "PNG", outFile1);

    Image transpImg2 = TransformColorToTransparency(image, new Color(0, 50, 77), new Color(200, 200, 255));
    BufferedImage resultImage2 = ImageToBufferedImage(transpImg2, image.getWidth(), image.getHeight());

    File outFile2 = new File(imagePath, "map_with_transparency2.png");
    ImageIO.write(resultImage2, "PNG", outFile2);
  }

  private Image TransformGrayToTransparency(BufferedImage image)
  {
    ImageFilter filter = new RGBImageFilter()
    {
      public final int filterRGB(int x, int y, int rgb)
      {
        return (rgb << 8) & 0xFF000000;
      }
    };

    ImageProducer ip = new FilteredImageSource(image.getSource(), filter);
      return Toolkit.getDefaultToolkit().createImage(ip);
  }

  private Image TransformColorToTransparency(BufferedImage image, Color c1, Color c2)
  {
    // Primitive test, just an example
    final int r1 = c1.getRed();
    final int g1 = c1.getGreen();
    final int b1 = c1.getBlue();
    final int r2 = c2.getRed();
    final int g2 = c2.getGreen();
    final int b2 = c2.getBlue();
    ImageFilter filter = new RGBImageFilter()
    {
      public final int filterRGB(int x, int y, int rgb)
      {
        int r = (rgb & 0xFF0000) >> 16;
        int g = (rgb & 0xFF00) >> 8;
        int b = rgb & 0xFF;
        if (r >= r1 && r <= r2 &&
            g >= g1 && g <= g2 &&
            b >= b1 && b <= b2)
        {
          // Set fully transparent but keep color
          return rgb & 0xFFFFFF;
        }
        return rgb;
      }
    };

    ImageProducer ip = new FilteredImageSource(image.getSource(), filter);
      return Toolkit.getDefaultToolkit().createImage(ip);
  }

  private BufferedImage ImageToBufferedImage(Image image, int width, int height)
  {
    BufferedImage dest = new BufferedImage(
        width, height, BufferedImage.TYPE_INT_ARGB);
    Graphics2D g2 = dest.createGraphics();
    g2.drawImage(image, 0, 0, null);
    g2.dispose();
    return dest;
  }

  public static void main(String[] args) throws IOException
  {
    AddTransparency at = new AddTransparency();
  }
}

Best Answer

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