Printing QImage to PDF

pantxo

Hi,

I use Qt for printing some graphics to PDF. Unfortunately, some QImages are not rendered correctly, I don't get the expected pixel colours.

I would expect the following code (adapted from this example https://wiki.qt.io/Exporting_a_document_to_PDF) to print a vertical image composed of 3 pixels : blue, green and red from top to bottom. Instead I get 3 pixels blue(Ok), light greenish, greenish (see attached pdf [0_1535805235367_toto.pdf](Uploading 100%) )

#include <QApplication>
#include <QtCore>
#include <QPrinter>
#include <QImage>
#include <QPrinter>
#include <QPixmap>
#include <QPainter>
#include <QFileDialog>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    QString fileName = QFileDialog::getSaveFileName((QWidget* )0, "Export PDF", QString(), "*.pdf");
    if (QFileInfo(fileName).suffix().isEmpty()) { fileName.append(".pdf"); }

    QPrinter printer(QPrinter::PrinterResolution);
    printer.setOutputFormat(QPrinter::PdfFormat);
    printer.setPaperSize(QPrinter::A4);
    printer.setOutputFileName(fileName);

    QPainter painter;
    painter.begin (&printer);
    
    QImage img (1, 3, QImage::Format_ARGB32);
    img.setPixelColor (0,0,QColor (Qt::red));
    img.setPixelColor (0,1,QColor (Qt::green));
    img.setPixelColor (0,2,QColor (Qt::blue));

    
    // Increase the apparent size of the image
    QTransform tform(55.8,0,0,-55.8,74.88,236.34);
    painter.setTransform (tform);
    
    painter.drawImage (QRect (0,0,1, 3), img);
    
    painter.end ();
    
}

What am I doing wrong?

Thanks,

Pantxo

pantxo

Oh, and if I modify the original example (see below) to print a 6 pixels image (red, red, green, green, blue, blue), then I get a better result but note that the two blue pixels don't have the exact same colour (see pdf attached)[0_1535807541749_toto.pdf](Uploading 100%) .

#include <QApplication>
#include <QtCore>
#include <QPrinter>
#include <QImage>
#include <QPrinter>
#include <QPixmap>
#include <QPainter>
#include <QTextDocument>
#include <QFileDialog>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    QString fileName = QFileDialog::getSaveFileName((QWidget* )0, "Export PDF", QString(), "*.pdf");
    if (QFileInfo(fileName).suffix().isEmpty()) { fileName.append(".pdf"); }

    QPrinter printer(QPrinter::PrinterResolution);
    printer.setOutputFormat(QPrinter::PdfFormat);
    printer.setPaperSize(QPrinter::A4);
    printer.setOutputFileName(fileName);

    QPainter painter;
    painter.begin (&printer);
    
    QImage img (1, 6, QImage::Format_ARGB32);
    img.setPixelColor (0,0,QColor (Qt::red));
    img.setPixelColor (0,1,QColor (Qt::red));
    img.setPixelColor (0,2,QColor (Qt::green));
    img.setPixelColor (0,3,QColor (Qt::green));
    img.setPixelColor (0,4,QColor (Qt::blue));
    img.setPixelColor (0,5,QColor (Qt::blue));

    
    // Increase the apparent size of the image
    QTransform tform(58.68,0,0,-58.68,268.74,384.48);
    painter.setTransform (tform);
    
    painter.drawImage (QRect (0,0,1, 6), img);
    
    painter.end ();
    
}

In case it may be relevant I use Qt 5.9 on linux Mint 19.

Thanks

pantxo

Nevermind, I found out that this is an already reported bug :

https://bugreports.qt.io/browse/QTBUG-54809

Pantxo