This is a page about a current exhibit of David Hockney's East Yorkshire landscapes at the L.A. Louver Gallery in Venice, California. There's a photo of him doing plein-air painting on SIX large canvases at once (to form a single painting). Now, that's encouraging. If he can paint six large canvases on location (at one time), how hard can it be to do one small one?
It's interesting that he doesn't use photography at all, even as a partial reference. He says the camera sees geometrically, but human beings see psychologically, which includes all of our perceptions, memories and feelings.