Java图像通道顺序变换（rgb转为bgr）

原理

• 要使得rgb和bgr互换，只需调换r和b通道。Java中借助BufferedImage进行转化，详见代码。
  

效果

Java代码

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

public class RGB2BGR {
	public static void main(String[] args) throws IOException {
		FileInputStream fileInputStream = new FileInputStream("d:\\rgb.jpg");
		byte[] imgBytes = new byte[fileInputStream.available()];
		fileInputStream.read(imgBytes);
		fileInputStream.close();
		BufferedImage bufferedImage = ImageIO.read(new ByteArrayInputStream(imgBytes));
		int width = bufferedImage.getWidth();
		int height = bufferedImage.getHeight();
        // 获取图片中每个rgb像素的int类型表示
		int[] rgbPixels = bufferedImage.getRGB(0, 0, width, height, null, 0, width);
		int[] bgrPixels = new int[rgbPixels.length];
		for (int i = 0; i < rgbPixels.length; i++) {
			int color = rgbPixels[i];
			int red = ((color & 0x00FF0000) >> 16);
			int green = ((color & 0x0000FF00) >> 8);
			int blue = color & 0x000000FF;
            // 将rgb三个通道的数值合并为一个int数值，同时调换b通道和r通道
			bgrPixels[i] = (red & 0x000000FF) | (green << 8 & 0x0000FF00) | (blue << 16 & 0x00FF0000);
		}
		bufferedImage.setRGB(0, 0, width, height, bgrPixels, 0, width);
		ImageIO.write(bufferedImage, "jpg", new File("d:\\bgr.jpg"));
	}
}

python代码

import cv2

img = cv2.imread('d:\\rgb.jpg')
img = img[:,:, (2, 1, 0)]
cv2.imwrite('d:\\bgr.jpg',img)

Java vs Python 代码量

Life is short, you need Python

参考文章

• https://www.cnblogs.com/roucheng/p/3527655.html
• https://blog.csdn.net/river66/article/details/89514816

思路来源

走过的弯路：ColorConvertOp只能在不同颜色空间之间相互转换，rgb和bgr都属于ColorSpace.CS_sRGB（可以调试观察BufferedImage的各个属性值），所以下面的转换是失败的，转换后的图片和转换前是一样的，因为都是同个颜色空间，所以底层只是做了复制，具体可以查看源码。

// 转RGB格式
// 参考：https://www.zhangshengrong.com/p/2EaE0rPR1M/
BufferedImage rgbImage = new BufferedImage(bgrImage.getWidth(), bgrImage.getHeight(), bgrImage.TYPE_3BYTE_BGR);
new ColorConvertOp(ColorSpace.getInstance(ColorSpace.CS_sRGB), null).filter(bgrImage, rgbImage);
ImageIO.write(rgbImage, "jpg", new File("d:\\rgb.jpg"));