Autostereograms are 2D images that use layering techniques to create a 3D effect, requiring the viewer to use cross-eyed or unfocused vision to detect the hidden image. Random dot and wallpaper autostereograms are common types, using grayscale images combined with color displays to create the illusion of depth.
An autostereogram, also known as a single-image stereogram, or SIS, is an image created using computer graphics that tricks the brain into perceiving a three-dimensional, or 3D, display when actually viewing a two-dimensional or 2D image. . Common types of autostereograms that include random dots and background images. 2D optical illusions that produce an effect of depth can usually be seen using specific focusing techniques. Instead of looking at the image itself, the viewer must use cross-eyed or cross-eyed focusing to detect the hidden image.
In a typical 2D image, overlapping colors, lines, and images create the illusion of depth using perspective. Lighter colors bring an object forward, and lines converging to a single point appear to recede into the distance. The eyes also perceive depth when objects are strategically placed opposite each other using a gradient of light to dark colors. A random autostereogram of dots or backgrounds uses layering techniques to produce a 3D image.
A random dot autostereogram first appears as a splash of millions of tiny dots or pixels. The dots could be black and white or very colorful. Layers of texture could also be added. Hidden within these dots is a design, object or word, initially produced in a grayscale gradient. This is generally a black and white image that uses lighting, shading, and rendering to form a multidimensional image.
Using a stereogram program, the artist joins the two images. Through camouflage, the edges of the grayscale image are slightly altered in color relative to the surrounding dots or pixels, but the colors throughout the image match the background.
Wallpaper autostereograms use a similar technique, except the 2D image generally contains repeating patterns, strategically placed horizontally or vertically at varying distances. The artists combine the color display with the grayscale image, and the edges of the grayscale image differ slightly from the surrounding colors. Viewing the hidden image contained within a random autostereogram of a spot or background will alter the visual line of focus.
Normally, when an individual looks at an image, each eye sees the image from a slightly different angle. The brain receives this information, creates a single composite image, and relays the information to the eyes. Recognizing hidden images in autostereograms generally requires changing the focus point from the image itself to a point beyond the stereogram. This type of impaired focus is commonly referred to as vision with closed eyes. Altering the focal point in this way is similar to looking through a window to see the scenery on the other side, where, eventually, the brain detects and reveals the closest image.
Cross-eyed 3D imaging involves two similar images placed side by side. In order for the brain to perceive depth, the viewer must change the focal point from the images to an area in front of the image, which passes through the eyes. This focal point joins the first two images and forms a third one, which creates the illusion of depth.
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