Molecular Depth Cues

Our class read about molecular depth cues this week.  These are aspects of a two dimensional image that allow us to interpret depth-- basically, how our brains perceive 3D.  Below are some screenshots, taken in Rocket World, that illustrate a few of these cues.

This first screenshot illustrates the concept of texture density.  The arrow to the left is pointing at the ripples in the water, which get smaller and smaller as they approach the horizon.  When our brain sees a texture pattern getting tighter and tighter, we interpret it as getting further and further away.  Eventually, the texture pattern becomes so small that we can only see the color (in this case, the dark blue just below the skyline.  

The second screenshot contains a number of molecular depth cues.  I will use the shiny orbs to illustrate my point.  The largest orb, just above my avatar's name, appears to be blocking parts of the objects behind it (to the right).  This is called occlusion-- objects that block out others are interpreted by the brain to be closer to the viewer.  The next depth cue that I would like to point out is size differences.  Though the rear orb (with the arrow pointing to it) appears to be much smaller than the large one above my avatar's name, it is actually the exact same size in Rocket World.  Meaning, if I walked my avatar over and stood next to it, it would tower over my avatar, just as the one in front of me now does.  However, since it is further away, it appears to be smaller through the human eye.  This is why it is harder to read football players' jersey numbers when you sit at the very top of the stadium!

The last depth cue that I will discuss, as illustrated by the screenshot above, is lighting and shading.  We can all tell that the "wooden" item slightly to the right of my avatar is a 3D cylinder, even though our computer screen is completely flat.  We do not even have to compare it to any other objects to know that it has height, width, AND depth.  Using basic lighting cues, our brain can see certain parts of this cylinder as being slightly farther away.  The light source (in this case the virtual sun in Rocket World) reflects more brightly off of the surfaces that are closest to it, which is why the top of the cylinder is brighter and color than the bottom.  Also, on the right of the cylinder (where the arrow is pointing) we see dramatic color changes over a short distance.  On the right side of the cylinder, the shadow is on top and the lighter side is on the bottom.  This lets us interpret a vertex, which is how our brain gives the item it's shape.