java glReadpixels to OpenCV mat

Question

I use lwjgl to render Images in OpenGL, now i want to store the content of the Framebuffer as RGB in an OpenCV Matrix. To make shure everything runs fine, im showing the captured image on Panel of a jFrame. But heres the problem: While showing stored jpegs everything looks fine but if im trying to show the captured Framebuffer i only see stripes!

Here is the code for a screenshot:

public Mat takeMatScreenshot()
{
    int   width       = m_iResolutionX;
    int   height      = m_iResolutionY;
    int   pixelCount  = width * height;
    byte[] pixelValues = new byte[ pixelCount * 3 ];

    ByteBuffer pixelBuffer = BufferUtils.createByteBuffer( width * height * 3 );

    glBindFramebuffer( GL_FRAMEBUFFER, m_iFramebuffer );
    glReadPixels( 0, 0, width, height, GL_RGB, GL_UNSIGNED_BYTE, pixelBuffer );

    for( int i = 0; i < pixelCount; i++ )
    {
        int line        = height - 1 - (i / width); // flipping the image upside down
        int column      = i % width;
        int bufferIndex = ( line * width + column ) * 3;

        pixelValues[bufferIndex + 0 ] = (byte)(pixelBuffer.get(bufferIndex + 0) & 0xFF) ;
        pixelValues[bufferIndex + 1 ] = (byte)(pixelBuffer.get(bufferIndex + 1) & 0xFF);
        pixelValues[bufferIndex + 2 ] = (byte)(pixelBuffer.get(bufferIndex + 2) & 0xFF);
    }

    Mat image = new Mat(width, height, CvType.CV_8UC3);
    image.put(0, 0, pixelValues);

    new ImageFrame(image);

    return image;
}

And here the code for displaying a Mat:

public static Image toBufferedImage(Mat m)
{
   int type = BufferedImage.TYPE_BYTE_GRAY;

   if ( m.channels() == 3 )
       type = BufferedImage.TYPE_3BYTE_BGR;

   if( m.channels() == 4 )
       type = BufferedImage.TYPE_4BYTE_ABGR;

   int bufferSize = m.channels()*m.cols()*m.rows();
   byte [] b = new byte[bufferSize];
   m.get( 0, 0, b ); // get all the pixels

   BufferedImage image = new BufferedImage( m.cols(), m.rows(), type );
   final byte[] targetPixels = ((DataBufferByte) image.getRaster().getDataBuffer()).getData();
   System.arraycopy(b, 0, targetPixels, 0, b.length);  
   return image;
}

It would be great if anyoune could help me! Cheers!

Answer 1

Oh no! Facepalm! The constructor of a OpenCV Mat Object is: Mat(rows, cols)! So the right solution is:

Mat image = new Mat(height, width, CvType.CV_8UC3);
image.put(0, 0, pixelValues);