The following is a feature article from Robert Maniscalco's monthly "Pointe of

Just wondering, didn't Caravaggio paint directly from life ?

The Da Vinci effect is essentially creating shadows the same height as the object and using a room painted linen/canvas in colour will do the rest. That is how we were trained.

If Hockney had been trained traditionally and used that training imaginatively, he would have figured out the rest of the techniques.

Steadman explains I believe some of Vermeer, but many of those paintings have normal sight. Once aware of an effect a trained artist can recreate it at will.