Thursday, November 1, 2012

Artist Tip #5 - Understanding Cast Shadows (Part 2)

Our last tip addressed the value (the relative darkness) of cast shadows.  This tip will focus on the direction of cast shadows in front- and back-lit scenes.  I'll specifically discuss shadows in sunny and moon-lit landscapes, but the same considerations apply for other light sources like lamps, and even multiple cast shadows caused by multiple light sources.

When painting a well-lit scene, we need not understand the theory of shadows.  We can simply paint the shadows as we see them.  It is when we are "adding" sunlight or moonlight to an overcast scene, rearranging the objects, or painting an entirely contrived scene, that we need to understand the theory of shadow directions so that our finished painting looks believable.

Let's first consider a sunny landscape with the sun above the top of our picture plane and behind the objects being painted, so that they are "backlighted".  Since the sunbeams travel in a straight line, any shadows cast by objects or people must lie along the line between the object and the sun.  This can be seen in the accompanying painting, appropriately named Shadows.

Here, the sun is positioned above the largest figure's head just above the top of the paper, and behind all of the objects in the painting.  You can see that the shadows approximately lie along a line drawn between the objects (the figures, or the boats) and the sun position.  But we have all heard that the sun is so far away that all its light beams are parallel, so... why are the shadows in this painting not parallel to one another?

The answer is that they are parallel.  Recall that in perspective, parallel lines converge to a vanishing point - in this case, the sun.  So it's a mistake to paint in the same direction all shadows that mainly come either forward or backward.  They need to be painted toward a vanishing point (roughly, not necessarily exactly).  This fact about shadows in paintings is not intuitive, so you may need to think about it, and even draw some lines up into your "sky", to fully make this fact your own.

I thought that two Artist Tips would take care of cast shadows, but I still have a little more to say about them.  Stay tuned for Part 3 in Artist Tip #6.

No comments: