(1) cv::Mat -> QImage
OpenCV存储图片默认使用BGR顺序，而QImage使用RGB顺序，所以需要用cvtColor转换一下。
使用QImage如下构造函数：QImage(uchar * data, int width, int height, Format format)
QImage mat2qimage(const Mat& mat) {
Mat rgb;
cvtColor(mat, rgb, CV_BGR2RGB);
return QImage((const unsigned char*)(rgb.data), rgb.cols, rgb.rows, QImage::Format_RGB888);
};
(2) QImage -> cv::Mat
QImage使用 RGBa(?) 四个通道保存图像数据，转换成的Mat应该删掉第四个通道。
Mat qimage2mat(const QImage& qimage) {
cv::Mat mat = cv::Mat(qimage.height(), qimage.width(), CV_8UC4, (uchar*)qimage.bits(), qimage.bytesPerLine());
cv::Mat mat2 = cv::Mat(mat.rows, mat.cols, CV_8UC3 );
int from_to[] = { 0,0, 1,1, 2,2 };
cv::mixChannels( &mat, 1, &mat2, 1, from_to, 3 );
return mat2;
}
3、QImage 转 IplImage（imageRGB32 --> originalImage）：
QImage imageRGB32(fileName);
QImage image = imageRGB32.convertToFormat(QImage::Format_RGB888);
IplImage *Oimage = cvCreateImageHeader(cvSize(image.width(), image.height()), IPL_DEPTH_8U, 3);
Oimage->imageData = (char *)image.bits();
IplImage *originalImage = cvCreateImage(cvSize(image.width(), image.height()), IPL_DEPTH_8U, 3);
cvConvertImage(Oimage, originalImage, CV_CVTIMG_SWAP_RB);
cvReleaseImageHeader(&Oimage);
4、IplImage 转 QImage（BGRimage --> Qimage）：
IplImage *BGRimage = cvLoadImage(filename, CV_LOAD_IMAGE_COLOR);
IplImage *RGBimage = cvCreateImage(cvSize(BGRimage->width, BGRimage->height), IPL_DEPTH_8U, 3);
cvConvertImage(BGRimage, RGBimage, CV_CVTIMG_SWAP_RB);
QImage Qimage((uchar *)RGBimage->imageData, RGBimage->width, RGBimage->height, RGBimage->widthStep, QImage::Format_RGB888);
cvReleaseImage(&BGRimage);
cvReleaseImage(&RGBimage);