QImage::loadFromData failing

  • I'm building an image viewer app for raw files (extracting the embedded jpeg). I am sending a list of all the image absolute paths to a function that:

    • extracts the embedded jpeg into a QByteArray

    • creates a QImage via loadFromData

    • creates a Pixmap via from Image

    • adds the Pixmap to QPixmapCache

      void ImageView::loadImageCache(QFileInfoList &imageList)
          QPixmapCache::setCacheLimit(10240000);   //10GB
          for (int i=0; i < imageList.size(); ++i) {
              QFileInfo fileInfo = imageList.at(i);
              QString imageFullPath = fileInfo.absoluteFilePath();
              QPixmap pm;
              loadPixmap(imageFullPath, pm);
              QPixmapCache::insert(imageFullPath, pm);
      void ImageView::loadPixmap(QString &imageFullPath, QPixmap &pm)
          QImage image;
          QFileInfo fileInfo(imageFullPath);
          QFile imFile(imageFullPath);
          QByteArray buf = imFile.read(mdCache->getLengthFullJPG(imageFullPath));
          bool imLoaded = image.loadFromData(buf, "JPEG");  // errors out after multiple calls
          pm = QPixmap::fromImage(image);

    When working on a folder with 36MP NEF files bool imLoaded becomes false and stays that way for all repeated executions for the remaining files in the folder after 5-6 files have been processed. When I send a folder of smaller jpegs I may get 30 files before imLoaded becomes false. The accumulated memory for the Pixmaps is usually around 1.2 - 1.4 GB when the image.loadFromData statement returns false. The memory estimate is based on (width * height * depth)/8 bytes. The QByteArray buf continues to work, no matter how many files I process.

    I'm hoping I am doing something obviously wrong. If not, I'm hoping someone can give me some advice on how to proceed to solve this.

    Running Qt 5.5 Win 10

    Thanks in advance

  • From QPixmap Documentation:
    Note that the pixel data in a pixmap is internal and is managed by the underlying window system.

    So, for Windows:

    • Pixmaps are stored as GDI-Objects
    • Memory for GDI-Objects is taken from windows paged kernel memory
    • paged kernel memory is limited by windows (on my 12GB win7 its around 1GB)

    If you really need to have 10GB of Images in memory you need

    • use QImage for storing data in memory
    • write your own Cache handling those Images
    • use Pixmap::fromImage(...) to display the Images

    Hope that helps

  • @Gerd

    Thanks Gerd. I'll start researching how to do that. Very much appreciated!


Log in to reply

Looks like your connection to Qt Forum was lost, please wait while we try to reconnect.