QImage inserted into QGraphicsTextItem looks fuzzy, when scaling QGraphicsTextItem

Hello,

Look into the attachment: screenshot.png

There is a problem with the "asdf" (QImage) in the QGraphicsTextItem: it is fuzzy. And that's because the QGraphicsTextItem is scaled with setScale(...).

I scale the QGraphicTextItem, because I want zoom the text in/out later in the programm. And yet I zoom it because the text should have the correct size in millimeters.

The text scaling works fine, but the "asdf" QImage will zoomed, too.

How to insert a QImage with high resolution, and make it smaller with scaling that the QImage doesn't looks fuzzy?
Or there other ways to solve this?

(An idea is to get the HTML of the TextItem and multiplicate all font sizes with the zoom level. But is there a better way?)

Thanks

Stefan Koch

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How to insert a QImage with high resolution, and make it smaller with scaling that the QImage doesn't looks fuzzy?

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Just the same as you did, just make the QImage size larger, and scale it to the result size you need.

But why don't you use QGraphicsTextItem?

I don't understand your question:

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But why don't you use QGraphicsTextItem?

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I use QGraphicsTextItem.

Quote:

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... make the QImage size larger, and scale it to the result size you need.

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How make a QImage size larger? Or: How to scale a QImage?

In my situation I set the scale of the QGraphicsTextItem a. e. to 1.5 (I make it greater, not smaller)

Thanks

Quote:

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I use QGraphicsTextItem.

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But you are using QImage for the 'asd' text as well - why?
I guess I don't understand what it is you are trying to do...

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How make a QImage size larger?

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QImage ( const QSize & size, Format format )
QImage ( int width, int height, Format format )
QImage scaled(...)

I have tested now, insert a scaledToHeight() image into the QGraphicsTextItem, the image is now smaller, but always the same rendering problem.

I have a QGraphicsTextItem with setScale it will be scaled.
see setScale(x)
if x<1
it works
if x>1
the inserted image get's fuzzy, it will be automatically zoomed, without enough information, a. e. the image is 15x15 pixel, now it will be automatically zommed by QT to 20x20 but the informations are only in 15x15, so QT must interpolate. Is is it possible to insert a Image with 150x150 pixel and zoom it to 10% that are enought informations here, and that's no interpolating needed if scale the QGraphicsTextItem to 1.5 (something higher as 1) - that's my idea of the problem - this idea could wrong


P. S. : I insert the image with a QTextCursor (cursor->insertImage(...))

I still fail to understand why you are using a QImage... what is it for?
Why not just let QGarphicsTextItem do the text rendering?
It will scale it correctly too!

Be as it may to your question:

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Is is it possible to insert a Image with 150x150 pixel and zoom it to 10%

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Yes as I said before, I probably just don't understand again - where is the problem?
Create the QImage 150x150 and scale it down to 15x15... You know how to create QImage which is 150x150, and you know how to scale it... so I don't see where is the problem?

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Why not just let QGarphicsTextItem do the text rendering?

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I have added a new screenshot to this answer, I hope this screenshot says all.
(Or is QGraphicsTextItem able to render LaTex?)

The third small image is the scaledToHeight(10) Image, it's fuzzy too.

The original sqrt-Image the alonestanding sqrt-png-file.

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Added after 8 minutes:

The unscaled QGraphicsTextItem is also attached as png-File (here is a red Text included, that says that this is unscaled)

I see.
Try turning anti aliasing off if its on and see if it helps.

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(Or is QGraphicsTextItem able to render LaTex?)

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QGraphicsTextItem probably doesn't render LaTex, but you might find this interesting:
http://doc.trolltech.com/solutions/4/qtmmlwidget/

Hello,

now I have disabled setRenderHint(QPainter::SmoothPixmapTransform) in QGraphicsView.
Antialiasing is not enabled in QGraphicsView.

See screenshot for details.

What's the problem?

Thanks

Hmm... I think this is just a scaling artifact. You don't see that with the text object (probably) because it really does render the text when scaled - and probably the line width is not as thin as it should be but a width that looks good at that size , but your QImage is just scaling it, making the lines thiner and when they are near each other you see the difference.
But that is just a guess.

What mean you with "lines"?

Did you enable smooth image transformations for your view?

@wysota
Do you mean this: setRenderHint(QPainter::SmoothPixmapTransform)
it was enabled in QGraphicsView in post #7 (see screenshot for details)

In general your image is of a very poor quality. The Nyquist law is merciless here.

So it does not work at all.
I have made a little test project. A MainWindow with a GraphicsView. I add the source code, if you want you can test it on your own computer (unzip the attachment TextItemTest.zip and compile it).

Note the attachment tex.png must be saved in your home folder (/home/<USER> on Linux).

And the third attachment shows you the screenshot of the little text project, including fuzzy sqrt-5 image NOW with 3600 dpi! (scaled to height 30 pix)

Thanks

A little code cutting form the test project:

Code:

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MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QDir dir;
    dir.cd(QDir::homePath());
 
    //ui->graphicsView->setRenderHint(QPainter::SmoothPixmapTransform);
    //ui->graphicsView->setRenderHint(QPainter::Antialiasing);
 
    QGraphicsScene *scene = new QGraphicsScene;
    ui->graphicsView->setScene(scene);
 
    QGraphicsTextItem *textItem = new QGraphicsTextItem;
    textItem->setTextInteractionFlags(Qt::TextEditorInteraction);
    textItem->setPlainText("test");
 
    QImage image(dir.absoluteFilePath("tex.png"));
    QImage imageScaled = image.scaledToHeight(30, Qt::SmoothTransformation);
    //QImage imageScaled = image.scaledToHeight(30);
 
    textItem->textCursor().insertImage(imageScaled);
 
    textItem->setScale(3);
 
    ui->graphicsView->scene()->addItem(textItem);
}

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P. S. set scale to 1 instead of 3 and it works fine
How is it possible to reply in a new post not by editing my old post (if nobody answered first)????

Wait a minute...

Code:

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textItem->textCursor().insertImage(imageScaled);
 
textItem->setScale(3);

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No wonder you get poor quality!
You put your DOWN scaled image, and scale it up x3 !!
You should do it so:

Code:

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QImage image(dir.absoluteFilePath("tex.png"));
QImage imageScaled = image.scaledToHeight(30, Qt::SmoothTransformation);
 
textItem->setScale(3);
 
textItem->textCursor().insertImage(imageScaled);

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You have to scale DOWN your LARGE image not UP the SMALL image!

Is the only change to my code to swap the lines 23. and 25. from post #15?

I can't see any change in your code improvement, as that you have swapped these lines, right?

Now the new code, with exactly the same issue:

What went wrong?

Code:

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MainWindow::MainWindow(QWidget *parent) :
    QMainWindow(parent),
    ui(new Ui::MainWindow)
{
    ui->setupUi(this);
    QDir dir;
    dir.cd(QDir::homePath());
 
    //ui->graphicsView->setRenderHint(QPainter::SmoothPixmapTransform);
    //ui->graphicsView->setRenderHint(QPainter::Antialiasing);
 
    QGraphicsScene *scene = new QGraphicsScene;
    ui->graphicsView->setScene(scene);
 
    QGraphicsTextItem *textItem = new QGraphicsTextItem;
    textItem->setTextInteractionFlags(Qt::TextEditorInteraction);
    textItem->setPlainText("test");
 
    QImage image(dir.absoluteFilePath("tex.png"));
    QImage imageScaled = image.scaledToHeight(30, Qt::SmoothTransformation);
    //QImage imageScaled = image.scaledToHeight(30);
 
    textItem->setScale(3);
 
    textItem->textCursor().insertImage(imageScaled);
 
    ui->graphicsView->scene()->addItem(textItem);
}

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Hmm... I don't know.

If you take your original large image, and scale it to 30 in an image editing application, does it look the same as the one you get with your code?

Yes, exactly.

See screenshot in this thread (test1.png).

I add the source code of the project (all headers, all cpps, ui-file, ...) this will be found in the TextItemTest.zip attachment of this thread. If you want you can test it on your own pc.

I add the tex.png, the 3600 dpi sqrt-5 file, too (to this thread).

Thanks.

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Yes, exactly.

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What yes exactly?
The image the edit application gets is the same results as your scaling in the application?