This is something I wrote a while back, maybe you'll find it usable
Qt Code: 
  1. void ImageViewer::saveFileAs()
  2. {
  3. 	// construct a filter of all supported formats
  4. 	QString filter;
  5. 	QList<QByteArray> formats = QImageWriter::supportedImageFormats();
  6. 	foreach (QString format, formats)
  7. 	{
  8. 		filter += QString("%1 files (*.%2);;").arg(format.toUpper()).arg(format);
  9. 	}
  10.  
  11. 	// remove unnecessary chars from the end of the filter
  12. 	if (filter.endsWith(";;"))
  13. 	{
  14. 		filter.chop(2);
  15. 	}
  16.  
  17. 	// get save file name
  18. 	QString selectedFilter;
  19. 	QString fileName = QFileDialog::getSaveFileName(this, 
  20. 		"Save image as", path, filter, &selectedFilter);
  21.  
  22. 	if (!fileName.isEmpty())
  23. 	{
  24. 		// keep track of the current path
  25. 		path = QDir(fileName).path();
  26.  
  27. 		// check for the selected format
  28. 		QString format = selectedFilter.split(" ").at(0);
  29. 		QFileInfo fi(fileName);
  30. 		if (!fi.suffix().endsWith(format, Qt::CaseInsensitive))
  31. 		{
  32. 			// remove possible incorrect suffix
  33. 			fileName.chop(fi.suffix().length());
  34.  
  35. 			// set correct suffix
  36. 			fileName += "." + format.toLower();
  37. 		}
  38.  
  39. 		// save image in the selected format
  40. 		if (!image.save(fileName, format.toAscii().constData()))
  41. 		{
  42. 			QMessageBox::information(this, "Image Viewer", QString("Unable to save %1.").arg(fileName));
  43. 		}
  44. 	}
  45. }
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