Saving QPixmap resutls in corrupt JPG

[Pit]

Hi! When I try to save a QPixmap in Windows, it results in a corrupt JPG file, black or black with white lines. But it doesn't happen in all computers, I tried in four and in two happens, in the other two not.

Saving in PNG doesn't have any errors.

Any ideas???

Thank you.

[wysota]

Please provide a minimal compilable example reproducing the problem.

[Pit]

Hi! Thanks for your reply. Here is the example that fails. Basically it loads a photo into a label and then saves it:

void MainWindow::on_savePushButton_clicked()
{
   [...]
 
    if (!photoLabel->pixmap()->save(QString("fotos/%1.jpg").arg(regLineEdit->displayText()), 0, 100))
      QMessageBox::warning(this, qApp->applicationName(), "Error");
 
   [...]
}
 
void MainWindow::loadPhoto()
{
  QPixmap pixmap;
 
  QString path = QString("fotos/%1.jpg").arg(cardsModel->index(mapper->currentIndex(), ViewCardsTableModel::Registration).data().toString());
 
  if (!pixmap.load(path))
  {
    QMessageBox::critical(this, qApp->applicationName(), QString("Error.").arg(cardsModel->index(mapper->currentIndex(), ViewCardsTableModel::Registration).data().toString()));
    photoLabel->setPixmap(QPixmap());
  }
  else
    photoLabel->setPixmap(pixmap);
}

void MainWindow::on_savePushButton_clicked()
{
   [...]

    if (!photoLabel->pixmap()->save(QString("fotos/%1.jpg").arg(regLineEdit->displayText()), 0, 100))
      QMessageBox::warning(this, qApp->applicationName(), "Error");

   [...]
}

void MainWindow::loadPhoto()
{
  QPixmap pixmap;

  QString path = QString("fotos/%1.jpg").arg(cardsModel->index(mapper->currentIndex(), ViewCardsTableModel::Registration).data().toString());
  
  if (!pixmap.load(path))
  {
    QMessageBox::critical(this, qApp->applicationName(), QString("Error.").arg(cardsModel->index(mapper->currentIndex(), ViewCardsTableModel::Registration).data().toString()));
    photoLabel->setPixmap(QPixmap());
  }
  else
    photoLabel->setPixmap(pixmap);
}

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[wysota]

This is neither minimal nor compilable.

[Pit]

Sorry, it's too much code. But it's simple, just this:

QPixmap pixmap;
pixmap.load("photo.jpg");
pixmap.save("photo2.jpg");

QPixmap pixmap;
pixmap.load("photo.jpg");
pixmap.save("photo2.jpg");

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Don't work. I get the attached image.

[wysota]

Does it happen for every jpeg image or this particular one?

[Pit]

For every JPEG, but if I use QImage instead QPixmap it works, so it's not because jpeg plugin (I think).

[wysota]

Well... saving the picture is done by the same code (QImageWriter) regardless if you use QPixmap or QImage as one is converted to the other so if it matters whether you use QPixmap or QImage, I'd say Qt is not to be blamed.

So the following doesn't work?

#include <QtGui>
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QPixmap px;
  px.load("input.jpeg");
  px.save("output.jpeg");
  return 0;
}

#include <QtGui>
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QPixmap px;
  px.load("input.jpeg");
  px.save("output.jpeg");
  return 0;
}

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And the following does?

#include <QtGui>
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QImage px;
  px.load("input.jpeg");
  px.save("output.jpeg");
  return 0;
}

#include <QtGui>
int main(int argc, char **argv){
  QApplication app(argc, argv);
  QImage px;
  px.load("input.jpeg");
  px.save("output.jpeg");
  return 0;
}

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Please check both snippets.

[Pit]

That's right, I checked it and the first doesn't work, the second does.

[wysota]

That's right, I checked it and the first doesn't work, the second does.

This exact same code, right? What platform are you using and which version of Qt (you might want to update your QtCentre profile to avoid such questions in future)?

[Pit]

Yes, this exact same code. I'm using Windows XP SP3 and Qt 4.6.3 (thanks for the advice ). This code works in another computer with XP SP3, but it doesn't in the computer with QT installed, neither in another with XP SP3 too.