@jsulm Got it solved it was in the textfile that I used to read into the QList because the value I gave is more than the number of elements in the text file that I read!

No and that's the point, I want to resize my image with the optimized size to display it.
The size could be the size maximum that I can load depending on the memory available.
And so my question is precisely, how to calculate this optimized size for resizing my image depending on the memory available, to display my image even if it is too large (in a QPixmap added within a QGraphicsScene through a QGraphicsPixmapItem)?