# How to Make a 3D Stereogram

By Steve Brachmann

Stereograms, also known as autostereograms, are optical illusions that depict an image within a picture that can be viewed while crossing your eyes. While staring at the 2D stereogram, you can detect a hidden image that will appear as a 3D object. Although a well-crafted stereogram takes time to accomplish, there has been an influx of graphic rendering software applications that make designing graphics such as stereograms easy.

## Viewing Stereograms

A person views a 3D image popping up from the background of a stereogram by crossing their eyes. This will cause a divergence of focal points between your eyes and send two different signals to your brain, creating a double vision effect. Images on a stereogram are printed so that two parts of an image converge as your eyes cross inward, and your brain is tricked into seeing a 3D image. Although simple stereographs known as stereo pairs can be constructed by placing an image next to a copy of itself, advanced rendering techniques can create two different images that, when they converge, better trick the brain into thinking it's viewing a 3D picture.

Find an autostereogram to practice viewing. If you can't find one readily available, you can find stereograms to view for free at www.eyetricks.com/3dstereo.htm. As you look at the image, gently begin to cross your eyes inward, which will cause the single image to appear as two images overlapping each other. Continue to view the image for approximately ten seconds in this manner, gently adjusting your eyes' focal points, until you begin to see a shape appear in the background; this is why many people call it "looking past the picture." Continue to fine tune your focus until your brain registers the 3D image.

## Drawing a Stereo Pair

You can create a stereo pair using graph paper and a pencil. Draw a 2D rendering of a cube on your graph paper with your pencil, drawing lightly so mistakes can be erased easily. A cube can be drawn in two dimensions by drawing two intersecting squares of equal dimensions on the graph paper, one slightly lower and left or right of the other, and connecting the closest corners. Move a few spaces left on your graph paper and repeat this image, using the same dimensions at the same level. Move your face to a foot's distance from the image, and begin to adjust your focal point. As you focus, the pair images should converge and create the impression of a 3D cube image.

## Text Stereogram

Using a word processor, you can create a text stereogram that will create a 3D effect depicting different depth levels. Though advanced stereograms depicting complex images can be created, simple stereograms can be completed in about 10 minutes.

Open your word processor. Use whatever software you're most familiar with, but the most basic word processing application will work. At the top of your image, type two asterisks ten spaces apart. You may need to return later and fine tune this, depending on the size of your image. Press 'Enter' to skip ahead a few lines and then type any character, such as the letter 'X'. Type the X and then move ahead a number of spaces in the line and type another X. Type as many Xs as you can in this manner, spacing each X evenly, until you reach the right margin. Skip ahead another few lines and type a new character, such as the letter 'Y.' Fill the line with evenly-spaced Ys in the same manner that you completed the line of Xs, but increase or decrease the Y spacing as compared to the X spacing by at least two spaces. If there are ten spaces between Xs, you can put eight spaces between Ys.

If you want, you can print this image, but you will be able to view the stereogram properly using your computer. Allow your focal points to diverge, crossing your eyes slowly until two of the asterisk doubles converge, creating the appearance of three total asterisks. As the letters begin to converge, the Ys will appear to be on a higher level than the Xs. If the stereogram was unsuccessful, go ahead and tweak your image to get the desired effect. Using this technique, you can experiment with advanced stereogram displays to create a more complex perception of 3D depth.

## Stereogram Software

Those who are familiar with graphics editing software, or any who would like to try, can utilize a few software applications to create enhanced stereographs. Blender is a 3D modeling program that is available for free use through the GNU General Public License. To obtain the program, visit www.blender.org, click 'Download' in the top margin, and select the version of Blender that is compatible with your operating system. Once installed, you can use Blender's graphics rendering tools to create an image that is shaded and highlighted to appear 3D. This image can be saved as a .tga file, where the asterisk is any given filename. The .tga image will appear in the stereograph as the 3D image.

GIMP, or GNU Image Manipulation Program is another software application available under the GNU General Public License. GIMP can be used to create the texture necessary to hide the 3D rendering created in Blender. A simple texture can be created by selecting the 'Tools' menu from the top margin, and then selecting 'Fill' to bring up an option menu of different texture patterns. A 'Pattern Fill' option available in the 'Tool Options' dialog box will expand the texture to fill the entire background. This texture can be saved as a *.png file, where the asterisk is any given filename.

These .tga and .png files can be compiled into a stereogram by using stereogram generating software. Stereogram Maker is a free program available for download through a number of Internet download portals, such as freewareapp.com. Stereogram Explorer is another program that will create stereograms from .tga and .png files, and a free trial is available at www.aolej.com/stereo. When looking for software, make sure to choose a download that is compatible with both .tga and .png files. These stereogram generators contain the proper algorithms for superimposing the .tga image into the .png textured background. This process will differ based on the software you choose.