Wednesday, November 23, 2011

3D using the Pulfrich effect a psycho-optical phenomenon

This has to be the crappiest 3D effect, certainly the least controllable and useful only as a gimmick.

It's a shame because the general public never understood any of this and it just gave 3D a bad name.

The Pulfrich effect is a psycho-optical phenomenon wherein lateral motion by an object in the field of view is interpreted by the brain as having a depth component, due to differences in processing speed between images from the two eyes. The effect is generally created by covering one eye with a really dark filter. The phenomenon is named for German physicist Carl Pulfrich who first described it in 1922.

In the classic Pulfrich effect experiment a subject views a pendulum swinging in a plane perpendicular to the observer’s line of sight. When a neutral density filter A lens which has been darkened, perhaps with grey for example, the pendulum is placed in front of the right eye seeming to be making an elliptical orbit, giving the illusion that it is closer as it swings to the right, and further away as it swings to the left.

The most accepted explanation for the noticeable depth is reduced retinal illumination. in terms of the other eye creating a signal delay due to the immediate spatial differences between objects in motion. The probable reason this seems to occur is due to the visual latencies which are normally shorter for The visual system reacts faster to targets that are bright in contrast to targets which are dim . (this was originally described by Carl Pulfrich , who was a German physicist) The moving object is observed in the retinal luminance and hence there is a difference in the signal latencies because of the distance between two eyes.

The Pulfrich effect, yielding about 15 meters, is scaled under real-life conditions with dark targets on a background of bright colors. delay for a factor of ten difference in average retinal luminance . These delays increase monotonically with decreased luminance over a wide (> 6 log-units) There is a vast spectrum of light. Also, this effect is seen as a bright target with a black background and shines with the same time period of brightness.

This effect could happen at any time in several diseases of the eye such as cataracts. Optic neuritis, or multiple sclerosis.  In these cases, symptoms that have been reported include having a hard time judging the paths of cars that are coming forward.

In visual media such as film and television, the Pulfrich effect is often used to produce 3-Dimensional imagery with Glasses. As in other kinds of stereoscopy, 3D glasses are used to create the illusion of a three-dimensional image. By placing a neutral filter (by way of example, the darkened sunglass lens)
covering one eye, an image, while moving back and forth. to the left or to the right, but definitely not up or down. 

Because the Pulfrich effect depends on motion in a particular direction to instigate the illusion of depth, it is not useful as a general stereoscopic technique; for example it cannot be used to show a stationary object apparently extending into or out of the screen; similarly, objects moving vertically will not be seen as moving in depth. However, the novelty effect is found in the visual scenario. One advantage of material produced to take advantage of the Pulfrich effect is that it is fully compatible with "regular" viewing without the need for "special" 3D Glasses.

This effect was somewhat popular in the 1990's. It was used, for example, in a 3D motion TV advertisement in 1990s, where objects moving in a particular direction seemed less distant to the viewer than others. viewing the front of a TV screen and they seemed to be further away from the viewer when moved in the opposite direction. behind the screen of a television set. To allow viewers to see the effect, the advertiser provided a large number of viewers with a pair of filters in a paper frame. In one eye the filter was more of a dark neutral gray and the other one was more transparent. In this instance, the commercial was restricted to objects only like skateboarders and refrigerators moving down a steep hill from left to right across the screen, a directional dependency determined by which eye was covered by the darker filter.

The effect was also used in the 1993 Doctor Who charity special Dimensions in Time and a 1997 special TV episode of 3rd Rock from the Sun. In many European countries, a group of short 3D movies made in the Netherlands were seen on TV. 3D Glasses were sold at a chain of gas stations. These short films were mainly travelogues of Dutch localities. An episode of The Power Rangers. uses "Circlescan 4D" technology and was given away through McDonalds. This is based on the Pulfrich effect. Animated programs that employed the Pulfrich effect in specific segments of its programs include The Bots Master and Space Strikers; they typically achieved the effect through the use of constantly-moving background and foreground layers. The famed Nintendo Entertainment System was known for using the effect along with their videogame Orb-3D. through keeping the player's ship continually moving and also included a set of 3D Glasses. So did Jim Power: The Lost Dimension in 3-D for the popular Super Nintendo gaming system, utilizing interesting and unique scrolling backgrounds to an especially great effect.

In 2000, 3D Pulfrich glasses were given to six million viewers in the United States and Canada for Discovery Channel's Shark Week.

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