OpenCV integration

OpenCV integration

1. is there someone out there working with both OpenCV and Qt 4.x already?
2. How can I display the captured frames in a Qt application?
3. Are there any recommendations as to which drawing functions should be used (e.g. which are faster?)

Basically you have two choices - either using or not using OpenGL. The first approach requires you to use QGLWidget and to display images by binding them as textures (using bindTexture()) and using those textures on a rectangle (preferably square one) which you display in the GL widget. With the other approach you will be displaying images on aQLabel object using QLabel::setPixmap(). The GL approach will be much faster but requires more coding.

// the individual channels for the IplImagetchannel0 = cvCreateImage(frame_size, IPL_DEPTH_8U, 1);tchannel1 = cvCreateImage(frame_size, IPL_DEPTH_8U, 1);tchannel2 = cvCreateImage(frame_size, IPL_DEPTH_8U, 1);tchannel3 = cvCreateImage(frame_size, IPL_DEPTH_8U, 1); // set all elements in tchannel0 (alpha channel) to 255cvSet(tchannel0,cvScalarAll(255),0); // with cframe being the captured frame (3 channel RGB)// and dframe the frame to be displayedcvSplit(cframe, tchannel1, tchannel2, tchannel3, NULL);cvMerge(tchannel1, tchannel2, tchannel3, tchannel0, dframe); // point to the image data stored in the IplImage*const unsigned char * data = (unsigned char *)(dframe->imageData); // read other parameters in local variablesint width = ocv_image->width;int height= ocv_image->height;int bytesPerLine = ocv_image->widthStep; // imageframe is my QLabel objectqimage = QImage( data, width, height, bytesPerLine, QImage::Format_RGB32 );ui.imageframe->setPixmap(pixmap->fromImage(qimage, 0));

#ifdef OPCAMENABLE #include "cv.h"#include "highgui.h"#include <stdio.h>#include <ctype.h> static QImage IplImageToQImage(const IplImage  *iplImage, uchar **data , bool mirroRimage = true ){  uchar *qImageBuffer = NULL;  int    width        = iplImage->width;   /*   * Note here that OpenCV image is stored so that each lined is 32-bits aligned thus   * explaining the necessity to "skip" the few last bytes of each line of OpenCV image buffer.   */  int widthStep = iplImage->widthStep;  int height    = iplImage->height;   switch (iplImage->depth)  {    case IPL_DEPTH_8U:      if (iplImage->nChannels == 1)      {        /* OpenCV image is stored with one byte grey pixel. We convert it to an 8 bit depth QImage. */        qImageBuffer = (uchar *)malloc(width * height * sizeof(uchar));        uchar *QImagePtr = qImageBuffer;        const uchar *iplImagePtr = (const uchar *)iplImage->imageData;        for (int y = 0; y < height; ++y)        {          // Copy line by line          memcpy(QImagePtr, iplImagePtr, width);          QImagePtr += width;          iplImagePtr += widthStep;        }      }      else if (iplImage->nChannels == 3)      {        /* OpenCV image is stored with 3 byte color pixels (3 channels). We convert it to a 32 bit depth QImage. */        qImageBuffer = (uchar *)malloc(width * height * 4 * sizeof(uchar));        uchar *QImagePtr = qImageBuffer;        const uchar *iplImagePtr = (const uchar *)iplImage->imageData;         for (int y = 0; y < height; ++y)        {          for (int x = 0; x < width; ++x)          {            // We cannot help but copy manually.            QImagePtr[0] = iplImagePtr[0];            QImagePtr[1] = iplImagePtr[1];            QImagePtr[2] = iplImagePtr[2];            QImagePtr[3] = 0;             QImagePtr += 4;            iplImagePtr += 3;          }          iplImagePtr += widthStep - 3 * width;        }      }      else        qDebug("IplImageToQImage: image format is not supported : depth=8U and %d channels\n", iplImage->nChannels);       break;     case IPL_DEPTH_16U:      if (iplImage->nChannels == 1)      {        /* OpenCV image is stored with 2 bytes grey pixel. We convert it to an 8 bit depth QImage. */        qImageBuffer = (uchar *)malloc(width * height * sizeof(uchar));        uchar *QImagePtr = qImageBuffer;        const uint16_t *iplImagePtr = (const uint16_t *)iplImage->imageData;         for (int y = 0; y < height; ++y)        {          for (int x = 0; x < width; ++x)            *QImagePtr++ = ((*iplImagePtr++) >> 8); // We take only the highest part of the 16 bit value. It is similar to dividing by 256.          iplImagePtr += widthStep / sizeof(uint16_t) - width;        }      }      else        qDebug("IplImageToQImage: image format is not supported : depth=16U and %d channels\n", iplImage->nChannels);       break;     case IPL_DEPTH_32F:      if (iplImage->nChannels == 1)      {        /* OpenCV image is stored with float (4 bytes) grey pixel. We convert it to an 8 bit depth QImage. */        qImageBuffer = (uchar *)malloc(width * height * sizeof(uchar));        uchar *QImagePtr = qImageBuffer;        const float *iplImagePtr = (const float *)iplImage->imageData;         for (int y = 0; y < height; ++y)        {          for (int x = 0; x < width; ++x)            *QImagePtr++ = (uchar)(255 * ((*iplImagePtr++)));          iplImagePtr += widthStep / sizeof(float) - width;        }      }      else        qDebug("IplImageToQImage: image format is not supported : depth=32F and %d channels\n", iplImage->nChannels);       break;     case IPL_DEPTH_64F:      if (iplImage->nChannels == 1)      {        /* OpenCV image is stored with double (8 bytes) grey pixel. We convert it to an 8 bit depth QImage. */        qImageBuffer = (uchar *) malloc(width * height * sizeof(uchar));        uchar *QImagePtr = qImageBuffer;        const double *iplImagePtr = (const double *) iplImage->imageData;         for (int y = 0; y < height; ++y)        {          for (int x = 0; x < width; ++x)            *QImagePtr++ = (uchar)(255 * ((*iplImagePtr++)));          iplImagePtr += widthStep / sizeof(double) - width;        }      }      else        qDebug("IplImageToQImage: image format is not supported : depth=64F and %d channels\n", iplImage->nChannels);       break;     default:      qDebug("IplImageToQImage: image format is not supported : depth=%d and %d channels\n", iplImage->depth, iplImage->nChannels);  }   QImage *qImage;  if (iplImage->nChannels == 1)  {    QVector<QRgb> colorTable;    for (int i = 0; i < 256; i++)      colorTable.push_back(qRgb(i, i, i));     qImage = new QImage(qImageBuffer, width, height, QImage::Format_Indexed8);    qImage->setColorTable(colorTable);  }  else    qImage = new QImage(qImageBuffer, width, height, QImage::Format_RGB32);    QImage gd0 = qImage->mirrored(false,mirroRimage);    *data = qImageBuffer;    QColor textColor = Qt::black;    QColor fillrectcolor = Qt::red;    QColor shapepicture = Qt::white;    QImage gd = gd0.scaledToWidth(350);    QDateTime now = QDateTime::currentDateTime ();    QString selectionText = now.toString("dd.MM.yyyy hh:mm:ss");    QPainter p(&gd);    p.setRenderHint(QPainter::Antialiasing, true);     QFontMetrics fm( qApp->font() );    int stringWidth = fm.width(selectionText);    int stringHeight = fm.ascent();    const int sx = gd.width() - stringWidth - 5;    QPen pen;    pen.setStyle( Qt::SolidLine );    pen.setWidth( 2 );    pen.setColor( textColor );    p.setPen( pen);    p.drawText(QPointF(sx - 1 ,gd.height() - 2 - stringHeight - 1),selectionText);    pen.setColor( fillrectcolor );    p.setPen( pen);    p.drawText(QPointF(sx,gd.height() - 2 - stringHeight),selectionText);   return gd;}   #endif