CODEWITHSUNDEEP
qtpyqt
whuiscool
whuiscool

Reputation: 75

PyQt/Qt: How to stretch an image in Qlabel widget?

I want to display an image in my app. I use QtDesigner to design UI, then use pyqt to coding. The problem is the image that will be shown is lager than the widget size on the UI. I refer to offical demo: QT - Widget Image Viewer Demo

add imagelabel and scrollArea, code as follows:

---- UI init ----
self.label = QtGui.QLabel(self.centralwidget)
self.label.setGeometry(QtCore.QRect(40, 140, 361, 511))
self.label.setSizePolicy(QtGui.QSizePolicy.Preferred,QtGui.QSizePolicy.Preferred)
self.label.setObjectName(_fromUtf8("label"))
self.scrollArea = QtGui.QScrollArea(self.centralwidget)
self.scrollArea.setGeometry(QtCore.QRect(40, 140, 361, 511))
self.scrollArea.setWidget(self.label)
self.scrollArea.setObjectName(_fromUtf8("scrollArea"))

---- function ----
filename = "./Penguins.jpg"
image = QtGui.QImage(filename)
pp = QtGui.QPixmap.fromImage(image)
lbl = QtGui.QLabel(self.label)
lbl.setPixmap(pp)
self.scrollArea.setWidgetResizable(True)
lbl.show()

but it doesn't stretch the image, even no scroll bar appear!

Upvotes: 6

Views: 32943

Answers (3)

Petrucio
Petrucio

Reputation: 5679

The default implementation of QLabel::setScaledContents wasn't working for me, since it didn't allow me to keep the aspect ratio when the images where larger then the label's maximum sizes.

This little helper will scale the image down to fit into a label's maximum size if needed (but not up), always keeping the aspect ratio:

/**
 * Fill a QLabel widget with an image file, respecting the widget's maximum sizes,
 * while scaling the image down if needed (but not up), and keeping the aspect ratio
 * Returns false if image loading failed
 ****************************************************************************/
static bool SetLabelImage(QLabel *label, QString imageFileName)
{
    QPixmap pixmap(imageFileName);
    if (pixmap.isNull()) return false;

    int w = std::min(pixmap.width(),  label->maximumWidth());
    int h = std::min(pixmap.height(), label->maximumHeight());
    pixmap = pixmap.scaled(QSize(w, h), Qt::KeepAspectRatio, Qt::SmoothTransformation);
    label->setPixmap(pixmap);
    return true;
}

Upvotes: 4

Ammar
Ammar

Reputation: 2017

You need to call self.label.setScaledContents(true);. So that QLabel will resize itself to the size of pixmap/image and scroll-bar will get visible. See this documentation.

Upvotes: 17

utrescu
utrescu

Reputation: 364

I do not use PyQt but the QtPixmap control has scaled() functions. You can resize the image before put in the label:

  • scaled()
  • scaledToHeight()
  • scaledToWidth()

This is the sample code I use in C++ to resize an image to the QLabel size: 

imatge.load("sprite.png");
QPixmap imatge2 = imatge.scaled(ui->label->width(),ui->label->height());

Upvotes: 0

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