QGraphicsPixmapItem repaint immediately

I use a QGraphicsPixmapItem to hold an image, and a scene holds the item, and a view is attached to the scene. The problem is that when I modify the image and call the item->update(), scene->update(), view->update(), the widget does no change at all. I think it is because the "update" will not immediately call the paint, so does anyone have some solutions?
Thanks!

If you change the QPixmap object, you will have to call setPixmap() again in order to see the changes in graphics item - QGraphicsPixmapItem doesn't have access to your original pixmap.