QImage::loadFromData failing

[Rory_1]

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::clear();
      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);
      imFile.open(QIODevice::ReadOnly);       
      imFile.seek(mdCache->getOffsetFullJPG(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
Rory

[Gerd]

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

[Rory_1]

@Gerd

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

Rory