Analyzing a Digital Image in a Way that is Useful to a Student of Art

When traditional artists are painting they will often look at their work in a dark room (or sometimes by candle light). This filters out most of detail information (which our eyes don´t perceive well in the dark) and also removes the color from an image. The artist is then free to asses the paintings all-important tonal structure as well as it´s large masses. There are many such tricks in the artist´s lexicon and they all serve to provide valuable feedback to the many complex structures that underpin a manufactured image. This feedback is especially useful to the student who is needful of an impartial reflection upon their progress. What are the equivalents to such tricks in digital practice? What unique visual feedback do they offer and how can it be used?