Hello all: Here is a painting (18" by 24") that I just did over the past two weekends. I am probably at 97% finished--the 3% will be the touch-ups that will go on probably for another month! This is the front of my house, and the painting is based off a photo that I took one weekend morning coming back from chores. I wanted to work with shadows, and to get a wide value range so this photo seemed perfect. In the end, I used pure titanium white for the front of the house to the left of the door. The burnt umber and alizarin crimson for the shadows around the inside edge of the door gave a very nice, and wide, contrast to the white.
Using only the 5 colors that Mark suggested has been a real boost in terms of converging to the color and value I wanted. While not always dead on of the sample photograph, I more often than not got very close on the color. It made for satisfying painting sessions.
For tools to help me with the painting, I used a grid system app that applied a grid onto the photo in my iPad. I also use a Brookstone mini projector (works with the iPad/iPhone) to check my alignments with the grid as the painting took shape. The perspective is tricky: the eye level is in line with the middle bar in the window on the left, and the vanishing point of the front facade of the house is in line with the edge of the house on the right, excluding the bay window. Additionally, the front door/foyer itself is at an angle, so the foyer surfaces have their own vanishing points. I had to redo the roof line of the foyer going into the house; the grid guides, which should have helped, started disappearing as they got painted over!
One "quick and dirty" way I found for checking values was to turn down the lights in the room. In dim lighting, the off values can be detected very quickly. The second photo I posted is one I took with dim lighting, and shows the effect. Whenever I notice that my painting still looks interesting in dim lighting, I know that something about it works!