Java BufferedImage setRGB，getRGB错误

Question

I am editing a BufferedImage.

After altering the pixel in the picture, I do a check to ensure the new value is what I expected it to be. However, they have not changed to the designated pixel Color !

I thought it could be something to do with the Alpha value, so I recently added a step that extracts the Alpha value from the original pixel, and ensures that value is used when creating the new Color to be inserted back into the image.

System.out.println(newColors[0] + ", " + newColors[1] + ", " + newColors[2]);
Color oldColor = new Color(image.getRGB(x, y));
Color newColor = new Color(newColors[0], newColors[1], newColors[2], oldColor.getAlpha()); // create a new color from the RGB values.
image.setRGB(x, y, newColor.getRGB());// set the RGB of the pixel in the image.

for (int col : getRGBs(x,y)) {
    System.out.println(col);
}

The method getRGBs() returns an array where

• index 0 is the Red value
• index 1 is green
• index 2 is blue.

The output looks like:

206, 207, 207
204
203
203

As you can see, the values 206, 207, 207 come back out of the image as 204, 203, 203 - in fact, every pixel I change comes back out as 204, 203, 203 . What am I doing wrong? It just doesn't make sense. Thanks in advance!

Answer 1

I found my own answer online, I'll summarise it below:

In BufferedImages with a ColorModel the pixel is set to the nearest colour chosen. That means that you might not get the colour you wanted because the colours you can set are limited to the colours in the ColorModel. You can get around that by creating your own BufferedImage and draw the source image onto that and then manipulate those pixels.

BufferedImage original = ImageIO.read(new File(file.getPath()));

    image= new BufferedImage(original.getWidth(), original.getHeight(), BufferedImage.TYPE_3BYTE_BGR);
    image.getGraphics().drawImage(original, 0, 0, null);
     for(int y = 0; y < original.getHeight(); y++){
            for(int x = 0; x < original.getWidth(); x++){
                image.setRGB(x,y, original.getRGB(x,y));
            }
     }

That solved the problem. Clearly, the ColorModel did not have the colours I had specified and thus adjusted the pixel to the nearest colour it could.

Source

Answer 2

I guess what you are looking for is WritableRaster which helps to write to the image read. Use ImageIO to write the final changes on to a new file or give the same file for altering.

   public class ImageTest {

    BufferedImage image;
    File imageFile = new File("C:\\Test\\test.bmp");

    public ImageTest() {
        try {
            image = ImageIO.read(imageFile);
        } catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    public void editImage() throws IOException {
        WritableRaster wr = image.getRaster();
        int width = image.getWidth();
        int height = image.getHeight();

        for(int ii=0; ii<width; ii++) {
            for(int jj=0; jj<height; jj++) {
                int color = image.getRGB(ii, jj);
                wr.setSample(ii, jj, 0 , 156);
            }
        }

        ImageIO.write(image, "BMP", new File("C:\\Test\\test.bmp"));
    }

    public static void main(String[] args) throws IOException {
        ImageTest test = new ImageTest();
        test.editImage();
    }

}