Physiology of Perception

How we see

Let's talk about you. Specifically, your physiology. You are the starting point of this whole process. It's not like we're making these images for aliens, right?

Ain't it great to be a primate

eyebrain.gif If you don't realize it already, let me tell you: your visual system is a stupendously marvelous thing. Until some kind of impairment of the system, most people never recongnize how seamless is the connection between the mechanical eyes and one's sense of self. It's amazing. Consider this: a photon enters the eye, strikes the retina, and collides with a cell with the ability to transfer the mechanical energy and trigger a chemical reaction which races through the brain to add its input to the extraordinary thought processes taking place every moment by the mind. Now multiply that by the actual number of photons and the awesome processing power of the mind. You're a genius just sitting there. Think of what it took just to read this.

Disparity: the key depth que

binoprlx.gif It may not look like much at first, but this illustration pretty much sums up how the most important 3D depth que works. Because your eyes are horizontally offset, each sees a slightly different representation of space. Here's a new keyword: Parallax - the apparent change in the position of an object resulting in a change in the direction or position from which it is viewed. Depending upon how far away objects in space are, these corresponding points in each image register farther apart (relative to each other) on the two retinae. Your mind observes this disparity and uses it to create a sense of three dimension depth from two planar displays. Disparity is the product of lens parallax (and lens focal length, but more on that later). The goal of stereography is to create an image pair that, when presented to the eyes (in a stereoscope), recreates this effect.

Cameras: the mechanical eye

eyecam.gif There are many similarities between your eye and a camera; and several significant differences of concern to the stereographer. For one, the FOV (Field of View) your eyes provide is much greater than that of a camera's. Although a wide angle lens may capture a full 180 degree sweep both vertically and horizontally, it comes at the price of distorting perspective. Another keyword: Perspective - picturing objects or a scene in such a way, e.g. by converging lines (linear perspective), as to show them as they appear to the eye with reference to relative distance or depth. More on this topic later. So, the point is, when working with cameras (and film), in order to maintain correct perspective, the FOV is less than human vision. This is usually done by presenting the image in a rectangular frame. The length of the sides of the rectangle in relation to each other is expressed as an aspect ratio. This concept comes in when discussing the Stereo Window.
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