None of that helped me, but I've changed fitInView's KeepAspectRatio to
Qt Code: 
  1. ui->graphicsView->fitInView(scn->sceneRect(),Qt::KeepAspectRatioByExpanding);
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Image is now little bigger than before, but that is not solution. Is there any other way to insert image into dialog's form, so I can apply images with all aspect ratios and there wouldn't be visible border?