Using OpenCV with Qt

The IplImage and Qt

In order to take advantage of the 500 algorithms offered by OpenCV, Qt applications have to manage iplImages. Therefore, converting QImageto/from iplImage is very important.

Converting QImage to iplImage

This snippet will convert QImages into iplImage with depth 8 and 3 channels. QImage can store data in several formats. This code accepts just 24-bit QImage::Format_RGB888 and theQImage::Format_RGB32. Apha values in the 32-bit format will be removed during the conversion.

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;

  }

Converting iplImage to QImage

This snippet will convert a iplImage with depth 8 and 1 or 3 channels into a 8/24-bit QImage.

Note: This code won't work for images with different depth and number of channels.

static QImage IplImage2QImage(const IplImage *iplImage)

{

    int height = iplImage->height;

    int width = iplImage->width;

 

    if  (iplImage->depth == IPL_DEPTH_8U && iplImage->nChannels == 3)

    {

      const uchar *qImageBuffer = (const uchar*)iplImage->imageData;

      QImage img(qImageBuffer, width, height, QImage::Format_RGB888);

      return img.rgbSwapped();

    } else if  (iplImage->depth == IPL_DEPTH_8U && iplImage->nChannels == 1){

	const uchar *qImageBuffer = (const uchar*)iplImage->imageData;

	QImage img(qImageBuffer, width, height, QImage::Format_Indexed8);

 

	QVector<QRgb> colorTable;

	for (int i = 0; i < 256; i++){

	    colorTable.push_back(qRgb(i, i, i));

	}

	img.setColorTable(colorTable);

	return img;

    }else{

      qWarning() << "Image cannot be converted.";

      return QImage();

    }

}

 

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