How to display a picture

[Payx]

So if i understand, i use QImage for doing whatever i want with this image.
And i use Qpixmax just for display in a label ?

(sorry for my english im not bilingual)

[Payx]

So if i want to calculate the size of my picture i use :

QSize QImage::size() const

The question is : how to use it ? there is no example

[mrjj]

@Payx said in How to display a picture:

QImage::size()

It returns a
http://doc.qt.io/qt-5/qsize.html
and you can ask it height / width etc
http://doc.qt.io/qt-5/qsize.html#height

const QSize MySize = theImage->size();

int h=MySize.height();

etc.
Update:
@wieland already showed ;)

[Payx]

Thanks but how to return it ?

""ui->label_3->setText( QString("Size: %1, %2").arg(s.width()).arg(s.height()) );""

there is not more simple ?

[mrjj]

@Payx
Well You need to convert to text anyway so it will become

ui->label_3->setText( "Size: " + QString::number(s.width()) +" "+ QString::number(s.width()) );

Not sure its better.

• Thanks but how to return it ?
  What we do there is to convert to text and set that text in some label.
  That is not really returning it.

returning it would be something like

QSize SomeFunc() {
return pm.size();
}

[Payx]

Thanks it works. I prefer : ui->label_3->setText( "Size: " + QString::number(s.width()) +" "+ QString::number(s.height()) );
because i understand all.

Then if i want to use height and width for other calcul i can use :
s.width() * 5 ?

If i want to cut my picture in many square or rectangle i have to do :

int h = s.width() and work with h thats right ?

[mrjj]

@Payx

• int h = s.width() and work with h thats right ?
  Yes that's a copy of the current width. ( so w is better name ;)
  but its makes the calculation easier to read than using s.width() directly.

Note to actually cut the image, you can use
http://doc.qt.io/qt-5/qimage.html#copy

[Payx]

Okay !

but : QImage QImage::copy(const QRect &rectangle = QRect()) const
with this code we can work only in one rectangle no ?

for example i thought cut my picture in pixels 4*4 and have a new image with resolution / 4 :

i have to use a code like this :

for (i=0,i<s.width()+1,i=i+4)
for (j=0,j<s.height()+1,j=j+4)

 end 

end

[mrjj]

@Payx

int step=4;
for (i=0,i<s.width()+1,i=i+step)
  for (j=0,j<s.height()+1,j=j+step)
  just use  QImage QImage::copy(int x, int y, int width, int height) const

This will generate small images of each 4x4

[Pradeep Kumar]

@Payx said in How to display a picture:

I put this "file:///C:/Users/David/Documents/addddd/r.jpg"

Yes i added a Qlabel with the .ui and named label (dont worry i changed the name in my code)

A small info, u can also place image in resource file of the project , so no need to worry about absolute path.

[Payx]

@mrjj said in How to display a picture:

@Payx

int step=4;
for (i=0,i<s.width()+1,i=i+step)
  for (j=0,j<s.height()+1,j=j+step)
  just use  QImage QImage::copy(int x, int y, int width, int height) const

This will generate small images of each 4x4

Okay i will test that.

I got an other question, with that code : "QImage img("C:/path/filename.jpg");" i have to put the destination of the file (sorry for my english)

but if i want to create a file explorer (for example in facebook we can change a picture with a file explorer and choose what picture i want)
what can i do ?

[mrjj]

• but if i want to create a file explorer (for example in facebook we can change a picture with a file explorer and choose what picture i want)

Im not 100% sure what you ask, but I give a guess:

Instead of using a fixed path in the program you can use
http://doc.qt.io/qt-5/qfiledialog.html
to let user browser and select an image.

Like in this example
http://doc.qt.io/qt-5/qtwidgets-widgets-imageviewer-example.html

so
QImage img("C:/path/filename.jpg"
becomes

QString imagefile = QFileDialog::getOpenFileNames(this, tr("Files"), QDir::currentPath(), tr("*.jpg *.png"));
QImage img(imagefile);

Hope that is what you asked about.

[Payx]

I found what i sought :

QStringList fileNames = QFileDialog::getOpenFileNames(this, tr("Open Image"),"/path",tr("Image Files (*.jpg)"));

But i got all files, and i just want .jpg for now """"""tr("Image Files (*.jpg)"));"""""""""" dont work ?

then i want to put my picture file in a label, but i can't find how to convert a QStringList to a Qimage or Qpixmap

[mrjj]

@Payx
it should work with *.jpg.

• but i can't find how to convert a QStringList to a Qimage or Qpixmap

Oh just use
fileName = QFileDialog::getOpenFileName(this,
tr("Open Image"), "/", tr("Image Files (*.png *.jpg *.bmp)"));

It only returns the 1 filename. ( NOTE THE MISSING s)

ui->mylabel->setPixmap( new QPixmap(fileName ));

[Payx]

I got one error : Expected one specifier before pixmap

[mrjj]

@Payx
the class is QPixmap
so its "new QPixmap"

setPixmap( new QPixmap(fileName ));

Sorry, was just fast code.

[Payx]

Yes i tried too before post but i had one error too, so i post the first error.

The second is :
No matching function for call to 'Qlabel::setPixmap(QPixmap*)"

[mrjj]

@Payx
Sorry not enough coffee :)

QPixmap pix(fileName );
setPixmap(pix);

[Pradeep Kumar]

If u are using QImage

m_imageLabel = new QLabel;
QImage imagePixmap;
imagePixmap.load(":/new/prefix1/Images/imageName.extension");
m_imageLabel->setPixmap(QPixmap::fromImage(imagePixmap));

Or

Only QPixmap

m_imageLabel = new QLabel;
QPixmap imagePixmap;
imagePixmap.load(":/new/prefix1/Images/imageName.extension");
m_imageLabel->setPixmap(imagePixmap);

imageName.extension can be image.png, image.jpeg.

[Payx]

@Pradeep-Kumar said in How to display a picture:

If u are using QImage

m_imageLabel = new QLabel;
QImage imagePixmap;
imagePixmap.load(":/new/prefix1/Images/imageName.extension");
m_imageLabel->setPixmap(QPixmap::fromImage(imagePixmap));

Or

Only QPixmap

m_imageLabel = new QLabel;
QPixmap imagePixmap;
imagePixmap.load(":/new/prefix1/Images/imageName.extension");
m_imageLabel->setPixmap(imagePixmap);

imageName.extension can be image.png, image.jpeg.

U didnt read the thread i think :-).
But thx

@mrjj Lol no problem :-)
Thanks it works i will create an other thread for an other question after