@VoidChen int 32 位，前八位存储 alpha 值，8-16 存储 R 值，16-24 存储 G 值，24-32 存储 B 值，& 与操作获取这些值，这些数据本来就是 8 位

灰度化可以直接这样处理
```java

public static void grayImage(File originalImg, File grayImg) throws IOException {
BufferedImage image = ImageIO.read(originalImg);

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

BufferedImage grayImageBuffer = new BufferedImage(width, height, BufferedImage.TYPE_BYTE_GRAY);
for (int i = 0; i < width; i++) {
for (int j = 0; j < height; j++) {
int rgb = image.getRGB(i, j);
grayImageBuffer.setRGB(i, j, rgb);
}
}

ImageIO.write(grayImageBuffer, grayImg.getName().split("\\.")[1], grayImg);
}

```