java - 无法从各个 BufferedImage 像素获取正确的 alpha 值

Question

我需要获取 RGBA 值，修改 RGB，然后再次设置 RGB(和 A)值。

但是，它似乎为所有像素返回 255，即使我知道我正在加载的图像中包含透明像素。

这是一个 SSCCE

import javax.imageio.ImageIO;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.File;
import java.io.IOException;

public class TestImage {

    public static void main(String args[]) {
        try {
            BufferedImage image = ImageIO.read(new File("/home/affy/Pictures/salamenceavatar.png"));

            BufferedImage buff = new BufferedImage(
                    image.getWidth(),
                    image.getHeight(),
                    BufferedImage.TYPE_INT_ARGB
            );

            Graphics2D g = buff.createGraphics();
            g.drawImage(image, 0, 0, null);

            for(int x = 0; x < image.getWidth(); x++) {
                for(int y = 0; y < image.getHeight(); y++) {
                    Color c = new Color(buff.getRGB(x, y));
                    int alpha = c.getAlpha();
                    System.out.println(alpha);
                }
            }
        }catch (IOException e) {
            e.printStackTrace();
        }
    }
}

Answer 1

使用Color(int, boolean)相反，传递 true 告诉它您想要从提供的打包 int

中提取 alpha 值

Color c = new Color(buff.getRGB(x, y), true);

来自 JavaDocs...

Creates an sRGB color with the specified combined RGBA value consisting of the alpha component in bits 24-31, the red component in bits 16-23, the green component in bits 8-15, and the blue component in bits 0-7. If the hasalpha argument is false, alpha is defaulted to 255.

Parameters:

rgba - the combined RGBA components
hasalpha - true if the alpha bits are valid; false otherwise