在 OpenCV 中将 `BufferedImage` 转换为 `Mat`

Question

How can I convert a BufferedImage to a Mat in OpenCV ?

I'm using the JAVA wrapper for OpenCV (not JavaCV ). As I am new to OpenCV I have some problems understanding how Mat works.

I want to do something like this. (Based on Ted W. reply):

BufferedImage image = ImageIO.read(b.getClass().getResource("Lena.png"));

int rows = image.getWidth();
int cols = image.getHeight();
int type = CvType.CV_16UC1;
Mat newMat = new Mat(rows, cols, type);

for (int r = 0; r < rows; r++) {
    for (int c = 0; c < cols; c++) {
        newMat.put(r, c, image.getRGB(r, c));
    }
}

Highgui.imwrite("Lena_copy.png", newMat);

This doesn't work. Lena_copy.png is just a black picture with the correct dimensions.

Answer 1

I also was trying to do the same thing, because of need to combining image processed with two libraries. And what I've tried to do is to put byte[] in to Mat instead of RGB value. And it worked! So what I did was:

1.Converted BufferedImage to byte array with:

byte[] pixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();

2. Then you can simply put it to Mat if you set type to CV_8UC3

image_final.put(0, 0, pixels);

Edit: Also you can try to do the inverse as on this answer

Answer 2

Don't want to deal with big pixel array? Simply use this

BufferedImage to Mat

public static Mat BufferedImage2Mat(BufferedImage image) throws IOException {
    ByteArrayOutputStream byteArrayOutputStream = new ByteArrayOutputStream();
    ImageIO.write(image, "jpg", byteArrayOutputStream);
    byteArrayOutputStream.flush();
    return Imgcodecs.imdecode(new MatOfByte(byteArrayOutputStream.toByteArray()), Imgcodecs.CV_LOAD_IMAGE_UNCHANGED);
}

Mat to BufferedImage

public static BufferedImage Mat2BufferedImage(Mat matrix)throws IOException {
    MatOfByte mob=new MatOfByte();
    Imgcodecs.imencode(".jpg", matrix, mob);
    return ImageIO.read(new ByteArrayInputStream(mob.toArray()));
}

Note , Though it's very negligible. However, in this way, you can get a reliable solution but it uses encoding + decoding. So you lose some performance. It's generally 10 to 20 milliseconds. JPG encoding loses some image quality also it's slow (may take 10 to 20ms). BMP is lossless and fast (1 or 2 ms) but requires little more memory (negligible). PNG is lossless but a little more time to encode than BMP. Using BMP should fit the most cases I think.

Answer 3

This one worked fine for me, and it takes from 0 to 1 ms to be performed.

public static Mat bufferedImageToMat(BufferedImage bi) {
  Mat mat = new Mat(bi.getHeight(), bi.getWidth(), CvType.CV_8UC3);
  byte[] data = ((DataBufferByte) bi.getRaster().getDataBuffer()).getData();
  mat.put(0, 0, data);
  return mat;
}

Answer 4

I use following code in my program.

protected Mat img2Mat(BufferedImage in) {
        Mat out;
        byte[] data;
        int r, g, b;

        if (in.getType() == BufferedImage.TYPE_INT_RGB) {
            out = new Mat(in.getHeight(), in.getWidth(), CvType.CV_8UC3);
            data = new byte[in.getWidth() * in.getHeight() * (int) out.elemSize()];
            int[] dataBuff = in.getRGB(0, 0, in.getWidth(), in.getHeight(), null, 0, in.getWidth());
            for (int i = 0; i < dataBuff.length; i++) {
                data[i * 3] = (byte) ((dataBuff[i] >> 0) & 0xFF);
                data[i * 3 + 1] = (byte) ((dataBuff[i] >> 8) & 0xFF);
                data[i * 3 + 2] = (byte) ((dataBuff[i] >> 16) & 0xFF);
            }
        } else {
            out = new Mat(in.getHeight(), in.getWidth(), CvType.CV_8UC1);
            data = new byte[in.getWidth() * in.getHeight() * (int) out.elemSize()];
            int[] dataBuff = in.getRGB(0, 0, in.getWidth(), in.getHeight(), null, 0, in.getWidth());
            for (int i = 0; i < dataBuff.length; i++) {
                r = (byte) ((dataBuff[i] >> 0) & 0xFF);
                g = (byte) ((dataBuff[i] >> 8) & 0xFF);
                b = (byte) ((dataBuff[i] >> 16) & 0xFF);
                data[i] = (byte) ((0.21 * r) + (0.71 * g) + (0.07 * b));
            }
        }
        out.put(0, 0, data);
        return out;
    }

Reference: here

Answer 5

I found a solution here . The solution is similar to Andriys.

Camera c;
c.Connect();
c.StartCapture();
Image f2Img, cf2Img;
c.RetrieveBuffer(&f2Img);
f2Img.Convert( FlyCapture2::PIXEL_FORMAT_BGR, &cf2Img );
unsigned int rowBytes = (double)cf2Img.GetReceivedDataSize()/(double)cf2Img.GetRows();

cv::Mat opencvImg = cv::Mat( cf2Img.GetRows(), cf2Img.GetCols(), CV_8UC3, cf2Img.GetData(),rowBytes );

Answer 6

One simple way would be to create a new using

Mat newMat = Mat(rows, cols, type);

then get the pixel values from your BufferedImage and put into newMat using

newMat.put(row, col, pixel);

Answer 7

To convert from BufferedImage to Mat I use the method below:

    public static Mat img2Mat(BufferedImage image) {
        image = convertTo3ByteBGRType(image);
        byte[] data = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
        Mat mat = new Mat(image.getHeight(), image.getWidth(), CvType.CV_8UC3);
        mat.put(0, 0, data);
        return mat;
    }

Before converting into Mat, I change the type of bufferedImage to TYPE_3BYTE_BGR, because to some types BufferedImages the method ((DataBufferByte) image.getRaster().getDataBuffer()).getData(); may return int[] and that would break the code.

Below is the method for converting to TYPE_3BYTE_BGR.

    private static BufferedImage convertTo3ByteBGRType(BufferedImage image) {
        BufferedImage convertedImage = new BufferedImage(image.getWidth(), image.getHeight(),
                BufferedImage.TYPE_3BYTE_BGR);
        convertedImage.getGraphics().drawImage(image, 0, 0, null);
        return convertedImage;
    }

Answer 8

When you use as JavaCP wrapper bytedeco library (version 1.5.3) then you can use Java2DFrameUtils .

Simple usage is:

import org.bytedeco.javacv.Java2DFrameUtils;
...
BufferedImage img = ImageIO.read(new File("some/image.jpg");
Mat mat = Java2DFrameUtils.toMat(img);

Note: don't mix different wrappers, bytedeco Mat is different than opencv Mat.

Answer 9

You can do it in OpenCV as follows:

File f4 = new File("aa.png");
Mat mat = Highgui.imread(f4.getAbsolutePath());