Showing QImage without converting to QPixmap

[travick]

I have some data:

uchar* imageData;

uchar* imageData;

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then;

imageData = static_cast <uchar*>(realloc(imageData, imageSize));
renderer->render(imageData, imageWidth, imageHeight, imageSize);

imageData = static_cast <uchar*>(realloc(imageData, imageSize));
renderer->render(imageData, imageWidth, imageHeight, imageSize);

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and showing image up:

QImage image(imageData, imageWidth, imageHeight, imageBytesPerLine, QImage::Format_RGB888); //I need only RGB
QPixmap pixmap = QPixmap::fromImage(image);
ui->imagePlace->setPixmap(pixmap);

QImage image(imageData, imageWidth, imageHeight, imageBytesPerLine, QImage::Format_RGB888); //I need only RGB
QPixmap pixmap = QPixmap::fromImage(image);
ui->imagePlace->setPixmap(pixmap);

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where
imagePlace is QLabel

Everything is all right until I want create image which takes lot of memory, for example size 8000px x 12000px
then allocated memory for imageData takes about 366MB (only 366MB).
Image still appears, but when doing

QPixmap pixmap = QPixmap::fromImage(image);
ui->imagePlace->setPixmap(pixmap);

QPixmap pixmap = QPixmap::fromImage(image);
ui->imagePlace->setPixmap(pixmap);

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Memory usage jump to above 700MB instead of 366MB

So my question is how to prevent this situation, because I want to show image which takes about 1GB or more, but in that situation memory usage is doubled (as far as I can see)!!

Is there way to direct display QImage on the screen?
What's more I wanna refresh this image several times (some kind of software generated animation)

I had search for reasonable solution but without success as far.

another strange thing:

when trying to display (in QLabel) image which has mode than 32767px width or height it fails, nothing is displayed.
It could be 32767px x 10px (takes only 959,97 KiB) and it shows correctly, but 32768px x 10px fails to show ...

[stampede]

Create a subclass of QLabel, reimplement paintEvent and draw the QImage with QPainter::drawImage.

[travick]

I subclassed QLabel

void ImagePlacer::paintEvent (QPaintEvent *event){
    if (image != 0)
    {
      this->resize(image->size());
      QPainter painter(this);
      painter.drawImage(this->rect(), *image, this->rect());
    }
  }

void ImagePlacer::paintEvent (QPaintEvent *event){
    if (image != 0)
    {
      this->resize(image->size());
      QPainter painter(this);
      painter.drawImage(this->rect(), *image, this->rect());
    }
  }

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but there is the same dobled memory usage ... It seem that problem is somewhere else, maybe in QPainter?

--
edit:
QPainter draws image by copying it's part, so there is the problem ....

solution - not resizing QLabel

void ImagePlacer::paintEvent (QPaintEvent *event){
    if (image != 0)
    {
      QPainter painter(this);
      painter.drawImage(this->rect(), *image, this->rect());
    }
  }

void ImagePlacer::paintEvent (QPaintEvent *event){
    if (image != 0)
    {
      QPainter painter(this);
      painter.drawImage(this->rect(), *image, this->rect());
    }
  }

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but I've to show scroll bars, to move over whole image ...

[jlemaitre]

Hi,

You can resize your QLabel-derived class at some other point (when setting the image for example) instead of resizing it each time in the paintEvent() handler.

void ImagePlacer::setImage (QImage * newImage)
{
    image = newImage;
    if (0 != image)
        resize (image->size());
}

void ImagePlacer::setImage (QImage * newImage)
{
    image = newImage;
    if (0 != image)
        resize (image->size());
}

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Added bonus: it will resize the widget only once instead of each time it is repainted.