I am write a paint program.
pix = QPixmap(600,500); // set size to 600X500
How to change size after this? Someting like:
pix.setSize(800,600); // Change size to 800X600
I think, QPixmap::scaled is what you need.
Returns a copy of the pixmap scaled to a rectangle with the given width and height according to the given aspectRatioMode and transformMode.
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I have a 4 channel png image with 8x8 Pixels that is loaded by a QImage. The QImage is then scaled by a factor of 200, so the image will have a new resolution of 1600x1600, each original pixel having a size of 200x200. But when this image is added to a QLabel through the means of a QPixmap and shown on screen, the drawn pixels will have slightly different sizes.
I've taken screenshots with Gimp and looked at the painted image more closely. It seems that every other pixel is slightly bigger than it should be, 201 instead of 200 pixels wide for example. The very last pixel in a row will then be smaller to compensate, so that the entire image has the correct size in the end.
This does not happen for all scaling factors, 100 is fine for example and so are factors that are a power of 2, such as 256.
My original approach was using a QGraphicsView and a QGraphicsPixmapItem in which case I scaled the GraphicsItem instead of the image. The effect was the same.
What effect am I seeing here? And what, if anything, can be done about it?
The code to reproduce this issue is very straightforward
int scale = 200;
image = QImage("some image file");
QPixmap pixmap = QPixmap::fromImage(image.scaled(image.size() * scale));
some_label->setPixmap(pixmap);
Turns out the easiest solution to my problem is to use QOpenGLWidget in the QGraphicsView:
setViewport(new QOpenGLWidget);
This single line in the constructor will result in much higher precision when scaling an image with the caveat of adding OpenGL as a dependency.
Another gotcha with this approach is that calling setViewport invalidates many of the settings done on a QGraphicsView. So if the view is set up in a UI file, as in my case, make sure to call other setters after calling setViewport.
I could not find a better solution that would work without OpenGL, short of writing my own rasterizer of course.
I have a qt label which by default has a place holder image in it:
self.label.setPixmap(QtGui.QPixmap(_fromUtf8("place_holder.jpg")))
There is a function to update the image contained in the label which is:
def selectFile(self):
image = QtGui.QFileDialog.getOpenFileName(None, 'Select Reference Image', '', '*.jpg')
self.label.setPixmap(QtGui.QPixmap(_fromUtf8(image)))
This works fine (the image is updated), but it is also deformed if the image used to update the label has different size from the place holder image.
Is there any way to fix this? I mean to adapt the image and to keep fix the size of the label?
You can try to set the scaledContents property:
self.label.setScaledContents(True)
self.label.setPixmap(QPixmap("your_image.jpeg"))
It works fine for me.
Beware that this scale the image to fill all available space. It means that the aspect ratio of the image wont be preserved unless the label size and the image have the same aspect ratio. You will have the same problem using the QPixmap.scale method as you can see in the images here.
Scale the image each time you import it. If you already have a size in mind for your label, you can even scale the place holder.
try (c++)
//initial setup
QPixmap pixPlaceHolder = QPixmap(_fromUtf8("place_holder.jpg");
QSize desiredsize = pixPlaceHolder.size(); // or any of the size you want
Each time you select a file:
label.setPixmap(QPixmap(_fromUtf8(image).scaled(desiredsize));
try this, this helped me for scaling the image to fit the label while maintaining the aspect ratio. Will also help to resize the image based on the label size.
pixmap = QPixmap(x)
pixmap = pixmap.scaled(self.label.size().width(),self.ui.label_4.size().height(), Qt.KeepAspectRatio)
self.label.setPixmap(QPixmap(pixmap))
I want to set pixmap to my QLabel. Problem is , not whole image is displayed in the label, i.e only small part of the image is displayed. Here is the code :
QPixmap pix("c:\\images\\myimg.png"));
mLabel->setPixmap(pix);
What can be the problem
Try setting pixmap size to label size
mLabel->setFixedSize(pix.size());
If you want to keep aspect ratio of the image you must do that:
QPixmap pix("c:\\images\\myimg.png");
pix = pix.scaled(QSize(mLabel->width(),mLabel->height()), Qt::KeepAspectRatio);
mLabel->resize(pix.size());
mLabel->setPixmap(pix);
If you don't want to keep aspect ratio of the image you must do that:
QPixmap pix("c:\\images\\myimg.png");
pix = pix.scaled(QSize(mLabel->width(),mLabel->height()), Qt::IgnoreAspectRatio);
mLabel->setPixmap(pix);
The Label was not added in layout. After adding it, it works.
I have two widgets, one arbitrary (usually a QLineEdit), and one QLabel which displays a Pixmap. They are placed next to each other with a QHBoxLayout. The widget with this layout is in turn placed in another layout.
Now, what I want is that the label with the pixmap is automatically resized so that it is as high as the arbitrary widget next to it. However, even when I set the label's sizePolicy to Maximum, it still seems to expand to the original pixmap size, instead of resizing the pixmap and shrinking to match the other widget. Instead of having two equally large widgets I have the arbitrary one which is smaller than the pixmap next to it.
Any ideas how to get the size of the pixmap label to match the size of the widget next to it?
How about:
int height = arbitraryWidget->height(); // get desired height.
label->setSizeHint(QSize(label->width(), height); // set size hint to current width and desired height.
label->setSizePolicy(QSizePolicy::Fixed); // optional, but this ensures size is desired.
How do I convert my font on a QGraphicsObject from point size to pixel size? I need to do this so the fonts will look right when I print my QGraphicsScene using QGraphicsScene::render().
Probably class QFontMetrics will do the job. Just create your desired QFont, set It's point size. Then create QFontMetrics object on your QFont.