I have a raster image in PNG format which I can open in QGIS but not in Windows Picture Viewer. To do that i figured out that I have to save my raster as a 'Rendered Image' from the 'Save As' (option by right-clicking on it in QGIS GUI).
So great then I could now open my rendered PNG in Windows Picture Viewer.
"Now I need a little help with as to how to do this (i.e. save the Raster as Rendered Image) without the QGIS GUI and via a Command Line"