save Qimage in a file

[ChrisW67]

The original code tries to write an inherently binary format, through a QTextStream, to a file named "out.png" and expects it not to get mangled. This is broken is several ways.

You want to write using the QIODevice::write() or writeData() function and a QByteArray containing the original PNG data.

Edit: I re-read the original post and changed the post entirely

[squidge]

I thought that but disregarded it when I read "but l can open the saved image on the disk with Infrview and other picture viewer", so obviously the picture get saved unmangled.

Unless of course I read the original post completely wrong.

[ChrisW67]

Fragile at best:

#include <QtGui>
#include <QDebug>
 
int main(int argc, char *argv[])
{
    QApplication app(argc, argv);
 
    QFile in("tawny.png");
    if (in.open(QIODevice::ReadOnly)) {
        QByteArray ba = in.readAll();
        in.close();
 
        QFile out("tawny_out.png");
        if (out.open(QIODevice::WriteOnly)) {
            QTextStream s(&out);
            s << ba;
            out.close();
        }
    }
 
 
    return app.exec();
}

#include <QtGui>
#include <QDebug>

int main(int argc, char *argv[])
{
    QApplication app(argc, argv);

    QFile in("tawny.png");
    if (in.open(QIODevice::ReadOnly)) {
        QByteArray ba = in.readAll();
        in.close();

        QFile out("tawny_out.png");
        if (out.open(QIODevice::WriteOnly)) {
            QTextStream s(&out);
            s << ba;
            out.close();
        }
    }


    return app.exec();
}

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With this image in:
tawny.jpg
(I cannot upload the output file: the forum thinks it isn't valid)
It has produced a broken header in the output:

chrisw@newton /tmp/simple_example $ file *.png
tawny_out.png: data
tawny.png:     PNG image data, 612 x 816, 8-bit/color RGB, non-interlaced
 
chrisw@newton /tmp/simple_example $ identify tawny*.png 
tawny.png PNG 612x816 612x816+0+0 8-bit DirectClass 750KBB 0.000u 0:00.010
identify: improper image header `tawny_out.png' @ error/png.c/ReadPNGImage/2842.

chrisw@newton /tmp/simple_example $ file *.png
tawny_out.png: data
tawny.png:     PNG image data, 612 x 816, 8-bit/color RGB, non-interlaced

chrisw@newton /tmp/simple_example $ identify tawny*.png 
tawny.png PNG 612x816 612x816+0+0 8-bit DirectClass 750KBB 0.000u 0:00.010
identify: improper image header `tawny_out.png' @ error/png.c/ReadPNGImage/2842.

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The file is broken at the very first byte of the 8-byte header by UTF-8 encoding of that byte:

chrisw@newton /tmp/simple_example $ od -tx1 -tc  -N 8 tawny.png 
0000000  89  50  4e  47  0d  0a  1a  0a
        211   P   N   G  \r  \n 032  \n
0000010
chrisw@newton /tmp/simple_example $ od -tx1 -tc  -N 8 tawny_out.png 
0000000  c2  89  50  4e  47  0d  0a  1a
        302 211   P   N   G  \r  \n 032
0000010

chrisw@newton /tmp/simple_example $ od -tx1 -tc  -N 8 tawny.png 
0000000  89  50  4e  47  0d  0a  1a  0a
        211   P   N   G  \r  \n 032  \n
0000010
chrisw@newton /tmp/simple_example $ od -tx1 -tc  -N 8 tawny_out.png 
0000000  c2  89  50  4e  47  0d  0a  1a
        302 211   P   N   G  \r  \n 032
0000010

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