QLabel显示视频不能跟随窗口随意放大或缩小解决方法

//Mat转QImage
QImage Widget::OpenCVMatToQImage(cv::Mat mat)
{

    // 8-bits unsigned, NO. OF CHANNELS = 1
      if(mat.type() == CV_8UC1)
      {
          QImage tempImage;
          //Mat转QImage
          tempImage = QImage(
                          static_cast<unsigned char *>(mat.data),
                          mat.cols,
                          mat.rows,
                          static_cast<int>(mat.step),
                          QImage::Format_Grayscale8
                      );
          return tempImage;
      }
      // 8-bits unsigned, NO. OF CHANNELS = 3
      else if(mat.type() == CV_8UC3)
      {
          // Copy input Mat
          const uchar *pSrc = (const uchar*)mat.data;
          // Create QImage with same dimensions as input Mat
          QImage image(pSrc, mat.cols, mat.rows, mat.step, QImage::Format_RGB888);
          return image.rgbSwapped();
      }
      else if(mat.type() == CV_8UC4)
      {
          // Copy input Mat
          const uchar *pSrc = (const uchar*)mat.data;
          // Create QImage with same dimensions as input Mat
          QImage image(pSrc, mat.cols, mat.rows, mat.step, QImage::Format_ARGB32);
          return image.copy();
      }
      else
      {
          return QImage();
      }
}

//设置QLabel显示图片
void Widget::setCam1ImageShow(cv::Mat src)
{

    QPixmap tempMap0 = QPixmap::fromImage(OpenCVMatToQImage(src));
    tempMap0 = tempMap0.scaled(
                ui->Cam1Label->size(),
                Qt::KeepAspectRatio,
                Qt::SmoothTransformation
            );

    ui->Cam1Label->setPixmap(tempMap0);

}

代码可以显示完整的图片，但会带来图片放大后无法缩小的问题，只需要在初始化阶段加上这一句就可以了

ui->Cam1Label->setSizePolicy(QSizePolicy::Ignored,QSizePolicy::Ignored);

默认

 缩小