Scaling a QImage with either height or width beyond qint16 max value yields fully transparent pixels in the target image.
The attached MWE shows the behavior: we start with a fully opaque white image of either INT16_MAX+1 in width or height, and 1 in height or width respectively. Then we scale the latter dimension to 2. The expected outcome would be a fully white image. In reality, the last pixel will be fully transparent.