How to clear pixel of BufferedImage in java?

问题

In java, I read an image and then go through the pixels and if its color distance is < 30, then I want to clear the image by changing its alpha to 0. This is my code:

But this is not working. It is having no effect...

Does anyone see the problem?

Thanks

import java.awt.Color;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;
import java.io.InputStream;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import javax.imageio.ImageIO;

public class Recognize {

    public static void main(String args[]) throws IOException {

        Path path = Paths.get("images/fish.png");
        File file = path.toFile();

        if (file.exists()) {
            InputStream stream = Files.newInputStream(path);
            BufferedImage bufferedImage = ImageIO.read(stream);

            int width = bufferedImage.getWidth();
            int height = bufferedImage.getHeight();

            if (width > 0 && height > 0) {
                int TLpixel = bufferedImage.getRGB(0, 0);
                Color TLcolor = new Color(TLpixel);

                for (int i = 0; i < width; i++) {
                    for (int j = 0; j < height; j++) {
                        int pixel = bufferedImage.getRGB(i, j);
                        Color color = new Color(pixel);
                        double distance = ColourDistance(TLcolor, color);
                        //System.out.println(distance);

                        if (distance < 30) {
                            int mc = (0 << 24) | 0x00ffffff;
                            int newcolor = pixel & mc;
                            bufferedImage.setRGB(i, j, newcolor);      
                        }
                    } 
                }



                File outputfile = new File("images/fish_new.png");
                ImageIO.write(bufferedImage, "png", outputfile);

            }
        }
    }

    public static int[] printPixelARGB(int pixel) {
        int alpha = (pixel >> 24) & 0xff;
        int red = (pixel >> 16) & 0xff;
        int green = (pixel >> 8) & 0xff;
        int blue = (pixel) & 0xff;
        return new int[] {red, green, blue, alpha};
    }

    public static double ColourDistance(Color c1, Color c2) {
        double rmean = ( c1.getRed() + c2.getRed() )/2;
        int r = c1.getRed() - c2.getRed();
        int g = c1.getGreen() - c2.getGreen();
        int b = c1.getBlue() - c2.getBlue();
        double weightR = 2 + rmean/256;
        double weightG = 4.0;
        double weightB = 2 + (255-rmean)/256;
        return Math.sqrt(weightR*r*r + weightG*g*g + weightB*b*b);
    } 
}

回答1:

By "clearing" the pixel you obviously meant "to make the pixel transparent".

In order to be able to make a pixel transparent, the image has to support transparent pixels. Whether or not a BufferedImage supports transparent pixels depends on the type of the BufferedImage. After loading a BufferedImage with ImageIO, you hardly know the type of the image. But you can easily convert the image into an image with a known type (that supports transparency) by passing it to a method like this:

public static BufferedImage convertToARGB(BufferedImage image)
{
    BufferedImage newImage = new BufferedImage(
        image.getWidth(), image.getHeight(),
        BufferedImage.TYPE_INT_ARGB);
    Graphics2D g = newImage.createGraphics();
    g.drawImage(image, 0, 0, null);
    g.dispose();
    return newImage;
}

来源：https://stackoverflow.com/questions/25346809/how-to-clear-pixel-of-bufferedimage-in-java

标签

java

pixel

bufferedimage

alpha