How to add watermark of one QImage with Qt ?

[mounipanditi]

I am trying to draw a watermark using QPainter ontop of Image and by reading QPainter i have managed to write the below code. But i am getting error messages on console

QImage image("/root/Desktop/rat.jpg");
QPainter painter(&image);
painter.setPen(QPen(Qt::green));
painter.setFont(QFont("Times", 72, QFont::Bold));
painter.setCompositionMode(QPainter::CompositionMode_Source);
QPoint point = QPoint( 150, 1250 );
painter.drawText( point, "!..Happy New Year..!" );
image.save("/u01/QtPractice/water/images/new_text.png");

Error:
Qt: Session management error: None of the authentication protocols specified are supported
libpng warning: iCCP: known incorrect sRGB profile
libpng warning: Interlace handling should be turned on when using png_read_image
QPainter::setPen: Painter not active
QPainter::setFont: Painter not active
QPainter::setCompositionMode: Painter not active
QPainter::end: Painter not active, aborted

Help to solve this,

Thanks in advance,
Mounika.P

[raven-worx]

@mounipanditi said in Painter not active:

/root/Desktop/rat.jpg

is this file really a JPG file? According to the error message it thinks it is a PNG?
If it is a JPG file make sure you've also deployed the Qt JPG image plugin.

[mounipanditi]

@raven-worx

Hi raven-worx, my bad a small change in the code as of your prediction it is PNG image only thanks for correcting. The reason is i am having images with same name both with PNG and JPG.

Can you please help me to create a water mark on image...!

[jsulm]

@mounipanditi Not related to your question: why on earth are you working as root on Linux?!

[joeQ]

@mounipanditi Hi, friend, you will know how to do it if you learned opencv.

Here, i writen a demo with qt now. shared for you. Just code snippet. not the all

The image is vaild for one mouth.

    /** ... */

    QString str = "/Users/XXX/work/imgs/M_01.jpg";
    if(img.load(str)){
        QImage mark(img.width()/2,img.height()/2,QImage::Format_RGB32);

        QPainter painter(&mark);
        painter.fillRect(0,0,mark.width(),mark.height(),Qt::yellow);
        QFont ft = painter.font();
        ft.setPixelSize(40);
        painter.setFont(ft);
        painter.drawText(0,0,mark.width(),mark.height(),Qt::AlignCenter,"Qt");

        QRgb rgbSrc,rgbMark;
        int r,g,b;
        float alpha = 0.6, beta = 1- alpha;

        for(int x = 0; x < mark.width(); x++){
            for(int y = 0; y < mark.height(); y++){
                rgbSrc = img.pixel(x,y);
                rgbMark = mark.pixel(x,y);
                /** note:  */
                r = int(qRed(rgbSrc) * alpha + qRed(rgbMark) * beta);
                g = int(qGreen(rgbSrc) * alpha + qGreen(rgbMark) * beta);
                b = int(qBlue(rgbSrc) * alpha + qBlue(rgbMark) * beta);

                r = (0 <= r && r <= 255) ? r : 0;
                g = (0 <= g && g <= 255) ? g : 0;
                b = (0 <= b && b <= 255) ? b : 0;

                img.setPixel(x,y,qRgb(r,g,b));
            }
        }

        if(img.save("out.jpg")){
            qDebug("Save Ok!");
        }
    }else{
        qDebug("img load failed!");
    }

    /** ... */

Maybe you should change the titel to "How to add watermark of one QImage with Qt ?", it will help others has the problem like you.

[mounipanditi]

Dear friend @joeQ,

             Thankyou for your reply.The snippet which you have posted was working fine.

Is there any possibility to remove the rectangle area around the watermark.

And i will change the titile as you have stated.

[joeQ]

@mounipanditi

did you read the code careful ? The code snippet is not complex. Yuo should read the code snippet and to leare them. why use this way.

[mounipanditi]

@joeQ
As per your suggesttion i'll make changes in the code on my own.Once again thanks for your help.