QProcess error to call mogrify

[mattia]

Hello, i was trying the QProcess class with a simple program, i made an interface to call mogrify program and convert an image. This is the code used to start the process:

void ConvertDialog::on_convertButton_clicked()
{
    QString sourceFile = sourceFileEdit->text();
    convertButton->setEnabled(false);
    outputTextEdit->clear();
 
    QStringList args;
    QString size = "-resize " + sizeComboBox->currentText().toLower();
    args << size << sourceFile;
 
    QString commandDebug = "command: ";
    int i;
    for(i = 0; i < args.size(); i++){
    	commandDebug += args.at(i);
    }
    textBrowser->setText(commandDebug);
    process.start("mogrify", args);
}

void ConvertDialog::on_convertButton_clicked()
{
    QString sourceFile = sourceFileEdit->text();
    convertButton->setEnabled(false);
    outputTextEdit->clear();

    QStringList args;
    QString size = "-resize " + sizeComboBox->currentText().toLower();
    args << size << sourceFile;
    
    QString commandDebug = "command: ";
    int i;
    for(i = 0; i < args.size(); i++){
    	commandDebug += args.at(i);
    }
    textBrowser->setText(commandDebug);
    process.start("mogrify", args);
}

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when i start it, it shows me this error:
mogrify: unrecognized option `-resize 800x600'.

but this option is available on mogrify. Any ideas?