Almost Anyone Can See a

Stereogram. Honest!

What You Need: A pair of these (Actual color may vary)

If you have never been able to see a 3D Stereogram, you're in for a magical experience. It's easy. All you need are two eyes, a Stereogram or two with which to practice, and a bit of patience. There are rare exceptions in which some people are physically unable to process stereographic information. And some people have vision problems that make it difficult or impossible to see stereo- graphically. But the good news is that the great majority of us were born with fully functioning stereographic vision and are perfectly able to enjoy the magic of 3D Stereograms.

How It Works

Each of our eyes sees the same scene but from a slightly different point, You can see this difference by looking out a window and alternately closing one eye and then the other eye and repeating this a few times. Whatever you are looking at will appear to jump back and forth. Your brain combines these two slightly different views into what we perceive as 3D depth. This is known as stereopsis. It's really not very hard. And the best part is after you have seen your first 3D Stereogram, it gets easier and easier to see the next and the next and the next.

The Mechanics of Parallel Vision

When you look at a photograph or read a book, your eyes slightly converge and focus directly on the text and/or the image you are looking at. When you look into the distance, your focus separates and becomes more parallel. It’s as if you keep stretching out the letter V. The two lines of the V become more and more parallel while still remaining connected. When you look at a stereogram, using the parallel viewing method, instead of focusing on the actual image, your focus should be as if you are viewing something a bit farther away, and that is behind the stereogram. As the greatest percentage of persons who can see stereogram, use the parallel method (not cross-eyed), this is how we design our stereograms.

Hidden Image Stereograms (HIS), made from seemingly random patterns are crafted from two components: the repeating pattern and the depth image. The specialized stereogram software we use reads the light and dark information from the depth map image and uses this information to create a magical 3D image. A depth map image is a black and white image comprised of 256 shades of gray that our software uses to create three dimensional depth. White comes to the very front and black goes all the way to the back. All the other shades of gray represent the layers of depth in between. It’s like slicing an objects into 256 thin layers. In real life, we identify a sphere, such as the example shown here in red, because it has a core shadow and a highlight. Without these "visual cues" it would just be a flat red circle. A sphere rendered as a depth map image (shown left) is very different. It is lighter in the center and becomes darker as it moves out to the edges. The diagram above shows how the roundness of the sphere is sliced into 256 thin layers. This is how sphere is interpreted by the Stereogram software.

The second component in a Hidden Image Stereogram is a repeating pattern such as the colorful flower pattern shown on the left. Our stereogram software repeats the pattern like wallpaper and makes subtle shifts to the pattern in each panel. When we view the stereogram our brain detects these changes and combines the subtle shifts to create the illusion of a 3D object. The Hidden Image Stereogram (above right) contains a 3D sphere. Patterns that are random and textured, such as the flowers, minimize the obvious pattern shifts, A well designed pattern also creates more depth and detail. The pattern in the stereogram shown above right repeats 6 times.

What Works and Does Not Work in a

Stereogram

A question we hear often is can you make a stereogram from a black and white photo? The answer is no. As explained in the last section, in order to create a hidden image for a stereogram, the image has to be created layer by layer from back to front. This can be done with a photograph but the process is very time consuming. The cost is reflected in the time it takes to craft the depth image. Text is always tricky, even short words or groups of words. Long words and complex logos don’t translate well into stereograms. Simple is always best. But we are willing to try anything. Almost.

For complex logos and/or text, a Mapped Texture Stereogram (MTS) is often the best solution, such as the image shown above. Or a hybrid stereogram with both a hidden and mapped texture layer. While much of the message may be visible, when viewed as a stereogram, the words pop up with impressive depth. Simple logos generally are very effective in Hidden Image Stereograms. In many cases we can also create hidden images of products and objects if they are not too complex.

The gramophone (the depth map image is shown on the left) in the HIS stereogram above is an example of a complex hidden image that works well as a hidden image. So do. Some don’t. Every stereogram is different. We’ve just touched upon the basics here. If you have any questions about the process, the cost, or length of time it takes to create a custom stereogram, or if you want to know if your message or logo will work as a stereogram, use our contact form or send us an e-mail and attach your image. Better still, give us your problem, and let us create the perfect solution. That’s what we love to do.

Viewing Stereograms

If you will be using stereograms for a project targeting a large audience or people with little or no viewing experience your primary concern will be with ease of viewing. There are multiple factors controlling this. Stereograms are created by repeating vertical patterns, textures, and/or objects. The horizontal distance between these repeats determines a parallax (visual displacement). If the width of this parallax is too wide it will strain a viewers eyes. If parallax is too narrow, the viewer will fuse too many vertical displacements at once and see extra layers that may fly in and out of focus: called double fusion. For experienced, practiced viewers there are advantages to a parallax that is very wide or narrow, but for ease of viewing, things must fall within a standard range. This standard range is in turn strongly affected by different factors. The most important factor is how distant the image is from the viewers face. Simply moving an image with broader parallax further away from your eyes effectively makes parallax narrower. Conversely, standard parallax coming closer to the viewers face will demand wider viewing technique. For the same reason, image size is a critical part of the equation when printing or posting a stereogram. The same image printed larger will have wider parallax than if printed smaller. Again, the viewer simply adjust the distance between their eyes and the image by moving forward or backward. In practice, an image that views properly and is easy to see at a large size can be problematic if reproduced at a smaller size where effective parallax becomes so small that double fusing is unavoidable. You might adjust this by bringing the image closer to your face, but there is a practical limit to this that may be determined by the quality of your screen or printed page, or your vision and eyeglasses, as well as ambient lighting. When a stereogram is required in several sizes, we prefer to create separate versions for optimal viewing at each size. As with everything else, no two people are alike. Aside from corrective lenses that may include progressive, bifocal, or trifocal compensation, there is subtle, but different spacing between individuals' eyes as well as differences in peripheral visions. Some people see the stereo 3D right away, others require time. This means basic viewing ability falls within the mean of a curve at best, rather than being alike for everybody. The reality is ease of viewing is seldom predictable when people view stereogram images.