当我读取图像像素时，像素Alpha始终为255

Question

In the following code example I set an Image pixel Alpha value to 70 but when I extract it again I get 255. Am I extracting it wrong or setting it wrong? what am I missing or not understanding.

public void createImage()
{


    BufferedImage img = new BufferedImage(2, 2,
            BufferedImage.TYPE_INT_RGB);

    //Set Pixel 

    int red = 50;
    int green = 10;
    int blue = 100;
    int alpha = 70;


    int col = (alpha << 24) | (red << 16) | (green << 8) | blue;

    img.setRGB(0, 0, col);  //Set pixel 0,0


    //Read Pixel

    int colint = img.getRGB(0, 0); //Get pixel 0,0


    Color newCol = new Color(colint,true);

    int alphaToPrint = newCol.getAlpha();
    int redToPrint = newCol.getRed();
    int greenToPrint = newCol.getGreen();
    int blueToPrint = newCol.getBlue();


    System.out.println("redToPrint :" +String.valueOf(redToPrint));
    System.out.println("greenToPrint :" +String.valueOf(greenToPrint));
    System.out.println("blueToPrint :" +String.valueOf(blueToPrint));
    System.out.println("alphaToPrint :" +String.valueOf(alphaToPrint));



}

The result when running the code :

What I expected is to get 70 when reading the alpha value :

int alphaToPrint = newCol.getAlpha();

Please help.

Answer 1

Your BufferedImage has no alpha channel ( TYPE_INT_RGB )

Use BufferedImage.TYPE_INT_ARGB instead (note the 'A')