OpenNI RGB image to OpenCV BGR IplImage conversion?

Question

The image which one can get from OpenNI Image Meta Data is arranged as an RGB image. I would like to convert it to OpenCV IplImage which by default assumes the data to be stored as BGR. I use the following code:

    XnUInt8 * pImage = new XnUInt8 [640*480*3]; 
    memcpy(pImage,imageMD.Data(),640*480*3*sizeof(XnUInt8));
    XnUInt8 temp;
    for(size_t row=0; row<480; row++){
        for(size_t col=0;col<3*640; col+=3){
            size_t index = row*3*640+col;
            temp = pImage[index];
            pImage[index] = pImage[index+2];
            pImage[index+2] = temp;
        }
    }
    img->imageData = (char*) pImage;

What is the best way (fastest) in C/C++ to perform this conversion such that RGB image becomes BGR (in IplImage format)?

Answer 1

Is it not easy to use the color conversion function of OpenCV?

imgColor->imageData = (char*) pImage;
cvCvtColor( imgColor, imgColor, CV_BGR2RGB);

Answer 2

There are some interesting references out there.

For instance, the QImage to IplImage convertion shown here, that also converts RGB to BGR:

static IplImage* qImage2IplImage(const QImage& qImage)
{    
    int width = qImage.width();
    int height = qImage.height();

    // Creates a iplImage with 3 channels
    IplImage *img = cvCreateImage(cvSize(width, height), IPL_DEPTH_8U, 3);
    char * imgBuffer = img->imageData;

    //Remove alpha channel
    int jump = (qImage.hasAlphaChannel()) ? 4 : 3;

    for (int y=0;y<img->height;y++)
    {
       QByteArray a((const char*)qImage.scanLine(y), qImage.bytesPerLine());
       for (int i=0; i<a.size(); i+=jump)
       {
          //Swap from RGB to BGR
          imgBuffer[2] = a[i];
          imgBuffer[1] = a[i+1];
          imgBuffer[0] = a[i+2];
          imgBuffer+=3;
       }
    }

  return img;
}

There are several posts here besides this one that show how to iterate on IplImage data.

Answer 3

There might be more than that (if the encoding is not openni_wrapper::Image::RGB). A good example can be found in the openni_image.cpp file where they use in line 170 the function fillRGB.