Stereogram

Stereogram of a Japanese Volcano

Visualizing a stereogram using a stereoscope

A stereogram is a graphic representation of three-dimensional objects on a flat medium, by means of their projections, using stereoscopy, so that they appear to have volume.

It is an optical illusion based on the way human eyes capture images from two different points of view. Those different perspectives are interpreted by the brain as a three-dimensional image.

Stereograms have been made for years, using two photographs taken from slightly different angles. However, RDS (Random Dot Stereograms), created with computer programs, and SIRDS, sometimes called autostereograms, have become more popular.

Types of stereograms

There are several types of stereograms, such as anaglyph, random dot stereogram, autostereoscopic image, autostereogram (or glasses-free 3D), or lenticular image.

Drawing a stereogram

The figure represents a method for drawing stereograms. The surface that we wish to represent, which is the blue line, is shown on a plane perpendicular to the paper; the paper, which is the green line, and the two eyes (OD, right eye and LE, left eye).

Since depth is perceived based on the disparity between the two eyes, we need to draw something that each of them interprets differently. To do this, we sweep the surface with horizontal lines that we will represent on the paper one by one.

How to draw a stereogram

1. We started with the first. We chose an arbitrary point of the surface, in figure 1. Tracing a straight between the left eye and the point, cut to paper in 1_iWhich is where the left eye sees point 1. Let's draw this point.
2. Below we trace the straight between point 1 and right eye, which gives us 1_d and we draw this new point, which is where the right eye sees point 1.
3. But since we can't stop the left eye from seeing it too, we'll take advantage of it as 2_i to draw the next point of the surface. For this we trace a straight line between the left eye and 1_d and we prolonged it to cut the surface. This gives us point 2.
4. Repeating step 2, we get 2_dWe draw on the paper and continue until the line is finished.

As described to draw from left to right, it must also be done from right to left. As this method gives us very scattered points, it starts with several close points, located between 1 and 2, which give us as many families to draw the complete line.

Then the process is repeated for the next line until the surface is completed in a regular and lawful manner.

As can be seen, the stereogram depends on physical parameters that are not arbitrary: interpupillary distance, distance from the eyes to the paper, and depth of the image. Before drawing a complex object, it is convenient to adjust these values with simple figures (a cone works very well) until depth perception is easily reached.

You can put the paper both in front of and behind the surface. If it is an object (a sphere for example) it is very curious to put the paper behind it, since in the stereogram you will see a sphere floating in the air, with the sensation of being able to touch it.

How to visualize a stereogram

To see a stereogram of random dots, the main thing is to understand the expected result. The idea is to blur the view of the image, in such a way that both perspectives are captured. Some recommend looking at infinity, that is, fix your eyes on a distant object and without blurring, try to look at the image. Others prefer to fix their eyes in the center while slowly zooming in on the image; It depends on each one and their visual condition.