图像的读取、缩小、保存

Image src = javax.imageio.ImageIO.read(new File(".\\pictures\\00.jpg"))
BufferedImage bufferedImage0 = new BufferedImage(w2,h2,  
                BufferedImage.TYPE_INT_RGB);       
        bufferedImage0.getGraphics().drawImage( 
                src.getScaledInstance(w2,h2, Image.SCALE_SMOOTH), 
                0, 0, null); 
//生成缩略图 上面的方法是将图片src平滑缩小到bufferimage里去
        ImageIO.write(bufferedImage0, "jpg", new File(".\\result\\0.jpg"));

public BufferedImage grayimage( BufferedImage bufferedImage) {
        BufferedImage bufferedImage2 = new BufferedImage(w, h,
                BufferedImage.TYPE_3BYTE_BGR);
        for (int x = 0; x < w; x++) {
            for (int y = 0; y < h; y++) {
                int argb = bufferedImage.getRGB(x, y);
                int r = (argb >> 16) & 0xFF;
                int g = (argb >> 8) & 0xFF;
                int b = (argb >> 0) & 0xFF;
                int grayPixel = (int) (r + g + b) / 3;        
                int rgb = (grayPixel * 256 + grayPixel) * 256 + grayPixel;
                if (rgb > 8388608) //8388608  = 256*256*256/2 是24位表示的最大数，最高位是符号位，再大就是负数表示了
                {
                    rgb = rgb - 16777216;
                }
                bufferedImage2.setRGB(x, y, rgb);
            }
        }
        return bufferedImage2;
    }