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Anaglyph images [by Admin]

Wed, 10 Oct 2007 18:19:34 +0200

General Information (Stereo Photography):: Anaglyph images
Anaglyph images are used to provide a stereoscopic 3D effect, when viewed with 2 color glasses (each lens a different color). Images are made up of two color layers, superimposed, but offset with respect to each other to produce a depth effect. Usually the main subject is in the center, while the foreground and background are shifted laterally in opposite directions. The picture contains two differently filtered colored images, one for each eye. When viewed through the "color coded" "anaglyph glasses", they reveal an integrated stereoscopic image. The visual cortex of the brain fuses this into perception of a three dimensional scene or composition.

Anaglyph images have seen a recent resurgence due to the presentation of images and video on the internet, CDs, and even in print. Low cost paper frames or plastic-framed glasses hold accurate color filters, that typically, after 2002 make use of all 3 primary colors. The current norm is red for one channel (usually the left) and a combination of both blue and green in the other filter. That equal combination is called cyan in technical circles, or blue-green. The cheaper filter material used in the past, dictated red and blue for convenience and cost. There is a material improvement of full color images, with the cyan filter, especially for accurate skin tones.

Video games, theatrical films, and DVDs can be shown in the anaglyph 3D process. Practical images, for science or design, where depth perception is useful, include the presentation of full scale and microscopic stereographic images. Examples from NASA include Mars Rover imaging, and the solar investigation, called STEREO, which uses two orbital vehicles to obtain the 3D images of the sun. Other applications include geological illustrations by the USGS, and various online museum objects.

Anaglyph images are much easier to view than either parallel sighting or crossed eye stereograms. However, these side-by-side types offer bright and accurate color rendering, not easily achieved with anaglyphs.

3D Film (term) [by Admin]

Mon, 14 Aug 2006 02:30:40 +0200

Stereo Cinematography:: 3D Film (term)
In film, the term 3-D (or 3D) is used to describe any visual presentation system that attempts to maintain or recreate moving images of the third dimension, the illusion of depth as seen by the viewer.

The principle involves taking two images simultaneously, with two cameras positioned side by side, generally facing each other and filming at a 90 degree angle via mirrors, in perfect synchronization and with identical technical characteristics. When viewed in such a way that each eye sees its photographed counterpart, the viewer's visual cortex will interpret the pair of images as a single three-dimensional image

Stereo 3D on computers [by Admin]

Mon, 14 Aug 2006 02:23:24 +0200

General Information (Computer Stereo):: Stereo 3D on computers
Numerous 3D rendering software is now available to easily play the power of computers. It allows more and more people, artists or engineers, to produce photo-realistic images.

Each time one needs to VIEW something unreachable with a camera, whether it is because it does not exist or is out of scale for human eyes, one can use a computer.

However, how realistic can those images be? Anyone looking at the computer screen can perfectly SEE that he is looking at an image, not directly at a real scene, or model.

This difference comes from the fact that in our three dimensional real world our two eyes give us two different images. This is because they are in two different positions in space, separated by an horizontal 2.5 inches offset (~ 6.5 cm). The brain accepts the small horizontal disparity between those two images, and in return gives a single image with accurate depth perception. This ability is known as stereoscopy.

Due to stereoscopy, you can perfectly notice the difference between a model car in a box and the image of it on the top of the box despite both having the same dimensions. Looking to the model, you see in stereo as each eye has its own image of the car model. But when looking at the image on the top, you see a flat image as both eyes are focused on the same image.

Now, as we know the difference between "flat viewing" and "stereo viewing", let's see how to use the first to create the second.

Creating a stereo image means first creating two flat images, i.e., a stereo pair: one image for the left eye and one for the right eye. This is easy to achieve: you render one image with the observer in the left eye position, apply an horizontal offset to the observer position and then render the right eye image. The offset is called the BASE in the stereoscopy vocabulary and is assumed to be the same as the inter-ocular distance (About 6.5 cm).

The base has to be increased or decreased relatively to the scale of the scene to have a significant stereo effect. Obviously, you cannot use the inter-ocular distance to view in stereo a chemical molecule or a galaxy. A typical average value for the base is 1/30 of the distance from the observer to the nearest object of a scene.

Why 1/30? If you stand in front of a window, which opens to a landscape to the horizon, you will notice that you cannot see clearly both the horizon AND the window itself if you stand within two meters away from the window.

When you are two or more meters away from the window, you can view all the scene comfortably from the nearest point (the window) to infinity (the horizon). This value of two meters depends on the person but is a statistical value. The fact is that 6.5 cm (inter-ocular distance) is about 1/30 of two meters.

So, if you take for the base 1/30th of the distance from the observer to the nearest object of the scene, you're sure that you will see the full stereo image comfortably from the first point until the last. You will also be able to see it with enough stereo sensation. When the base is larger than the average inter-ocular distance, the resulting stereo is called hyper-stereo. It gives you the sensation of looking at reduced models, as if you were a giant. On the other hand, when the base is smaller than the average inter-ocular distance, the resulting stereo is called hypo-stereo. It gives you the sensation of looking at enlarged models, as if you were a Lilliputian.

An error that needs to be avoided is making a stereo pair with converging viewing axes. It appears natural to use convergence since eyes converge while they are looking at something, although it is not the right way. When your eyes converge, the point at which they converge appears perfectly clear. The fact is that everything else appears blurry but you don't notice it because you are used to it. However, due to the accomodation reflex, when you look at something blurry your eyes will naturely adjust to it. In a stereo image, all the image has to be sharp to be viewed clearly at whatever point you look in the image. Converging on one point would make the image comfortable for all points in front of the converging point. However, this would be difficult for points behind it to fuse. By converging at infinity, i.e. by keeping viewing axes parallel, the whole image will be easy to fuse.

Things become a little more complex when you want to see in stereo a stereo pair . . . To fuse the two images you've produced in a stereo one, each eye must see only its own image. Different solutions have been found over the years, mainly a result of the use of stereo pairs from stereo cameras used during the 1950's and 1960's. You can use a lens stereoscope but you will have to transform your two images onto slides. You can also use a mirror stereoscope (if you can find one ...) but you will have to print your images.

It's possible to directly use the computer screen but that will divide the usuable surface on the screen into two; as you will have to display the two images side by side. If you do not have stereoscope, you could train to "free-view" by crossing your eyes with the right view on the left and the left view on the right as many stereo enthusiasts do. You will need time and patience as it is not totally obvious . . .

The best known solution is to write your own "SoftStereo" code. Then, use LCD shutter glasses.

The trouble is that this solution is not adapted for your aim if you just want to make some stereo images yourself. You can do this out of curiosity to see what it looks like by using your own computer and software you are accustomed to.

To do so in a cheap and quick way is absolutely possible, but (of course there is a "but") there will be some restrictions about the kind of images you will be able to convert properly into stereo. However, that will give you the opportunity to verify by yourself the interest to escape "flatland".

Computer images are displayed on color screens and those screens use the RGB (Red, Green, Blue) system to create the color of each pixel of the image. That means all computer images are made with three channels: a red one, a green one and a blue one. Suppose now we have tools to take only one color channel from an image. If we take the red channel from the left image and the blue channel from the right image, we will just need a tool to glue those two channels together and we will have a computer anaglyph giving black and white stereo when wearing anaglyph glasses with the red filter in front of the lefteye and the blue filter in front of the right eye.

Numerous software to manipulate images and to translate them between the different formats can be used to process the color channels and produce 3D. You just need tools which allow the separation of channels and allowing black and white images to be glued back as color channels; thus producing a color image.

If you rush immediately to convert your own stereo pairs into red-blue anaglyphs by playing with the RGB channels you will probably be disappointed. First, you will only have magenta and white stereo images, not really black and white ones (Red + blue = magenta). Secondly, stereo images are definitively not flat images and special manipulations have to be applied to them for correct viewing.

Magenta and white stereo is not interesting, black and white should be better, but color should be much more interesting. So, how can we produce color stereo images on the screen? Flat color images are made with three channels. This means that the three channels will probably also have to be used for color stereo. From which image will we have to take the green channel? Red and green filters are opposite and turn to dark if added. In contrast, blue and green filters are not opposite and turn to cyan if added. The green information has to come from the same filter as the blue. This means that the blue and green channel will both have to come from the same image: the right one.

Why use the red filter on the left and the cyan on the right? It could be the reverse but the International Stereoscopic Union has chosen the red on left for standard disposal. It is also in coordination with the red used in international marking such as: ships, planes, and politicians!

Now, if you convert a stereo pair into a color anaglyph by separating the channels and after gluing them back together, you will be able to see in stereo and in color directly on your monitor by just using red-cyan anaglyph glasses. It's that easy!

If you do not have anaglyph glasses with a cyan filter, you can use ones with a blue or a green filter: the stereo 3D effect will remain, but colors will change. With a blue filter, colors will slightly shift to blue. Avoid green anaglyph glasses as the green filter really wipes out too many colors.

Things are a bit more complex than they should be relating to the previous explanations.

The fact is that not all images can be converted. Images with strong contrast zones are definitively not suitable. They produce what stereo addicts call "ghosting". Strong contrast zones produce anaglyphs with too close and too strong red and cyan spots. This produces a very uncomfortable sensation through the red-cyan glasses. Images with large zones of saturated colors will produce "ghosting" too. All the left information comes from one color, red. If your image has large red zones, there will be no information (No green nor blue) for the right eye about those zones. No stereo effect will appear there. The same trouble happens with green and blue zones. There is nothing to do for images with strong contrast (except for creating the same image without the strong contrast . . . For example, you can change a black background into a grey background or you can try to change the lighting), even though it is still possible to use images with saturated colors. If those saturated zones were gray there should be no problems as all the three channels should be the same on the zones.

Therefore, we have to find a solution that will shift colors to grays but, yet respect the balance of space information between the two eyes. This solution should also respect the original colors (if possible) and the three color channels. The solution will be to modify the saturation of the images. Modifying saturation will allow us to modify the quantity of colors in an image by keeping for the resulting image only a few percentages of colors from the original image. Notice that fully decreasing saturation turns the image into some kind of black and white version still coded on RGB. The correct way to produce really black & white images is to use a dedicated tool. (We will see later where is the difference.) A tool converting into Black and White will allow us directly to produce black & white stereo images.

Saturation 0 is the ultimate weapon against saturated spots. The trouble is that it wipes out all colors. It would be better if it were possible to modify the colors wiping out only the spots that produce "ghosting". A way to do this is to use an image processing software to change the hue or to reduce the saturation of the spots before producing the anaglyph. The fact is that using an image processing software, fighting the ghosting can be long and tedious. This does not suit our original aim to produce stereo images in a quick way. We will therefore use another concept, the Chopin & Lanfranchi method, based on the fact that main problems with ghosting come from red and green.

In blue zones, ghosting is very light and is often ignored by viewers, so we can keep the blue channel from the right image without any change. Red and green channels have to be modified to decrease the difference between red and green contributions on each pixel. On a black and white image, there is no difference between these two channels; they are exactly the same. That's why there are no ghosting problems with black and white stereo 3D. We will therefore take red and green channels from the black and white versions of the left and right images.

There are two other simple ways to modify red and green channels to wipe out ghosting colors. Software which converts color to black & white images makes some kind of average calculation between the three channels to produce a single black and white channel. The formula used to get one value from three is: black & white = 0.30 red + 0.59 green + 0.11 blue. 0.30, 0.59 and 0.11 are values related to the sensitivity of the human eye. We can make similar calculations to obtain other average values. We will produce images shifting to yellow if we use the following formula: new value = 0.50 red + 0.50 green = average (red + green) We will produce images shifting to gray if we use the following formula: new value = 1/3 red + 1/3 green + 1/3 blue = average (red + green + blue)

The result of such manipulations is to shift the colors to shades of dark green and brown, yellow, or gray. It is not very aesthetic but it works perfectly well with red-cyan glasses ...

All those tricks should allow you to find quickly a comfortable anaglyph version from most of your stereo pairs.

In anaglyphs, and more generally in all stereo images, we find that they are not images but volumes. Specific rules, which are not in use with flat images, have to be respected to display the volumes.

Unless you are standing alone with nothing more than the horizon and the sky around you, space appears relative to some frontiers. This is what happens when you look through a window. In the case of a stereo image displayed on a computer screen, the four physical sides of the screen (Left, right, top and bottom) are absolute frontiers. They build a window through which you can see the stereo reconstructed space. That introduces the following specific restriction: if any side of the images of a stereo pair cuts any part of the scene, this part must stand just beside the screen borders on the stereo image. That means that you cannot see in front of a window something that is too large to go through this window. The spatial coherency has to be respected between the stereo scene and the screen that displays it.

Very often you will have to move your stereo image back into the screen . If you don't do it, you will produce stereo images viewers will not be able to fuse. A typical reason is that points that normally should be at infinity (or at least far away) will lie just on the plane of the screen. They will have quite no parallax. This will make an aberrant springing stereo image, completely out from the screen.

In general [by Admin]

Mon, 14 Aug 2006 02:10:29 +0200

Anaglyph Software:: In general
Anaglyph images have seen a recent resurgence due to the presentation of images on the internet. Where traditionally, this has been a largely black & white format, recent digital camera and processing advances have brought very acceptable color images to the internet and DVD field. With the online availabilty of low cost paper glasses with improved red-cyan filters, and even better plastic framed glasses, the field is growing fast. Scientific images, where depth perception is useful, include the presentation of complex multi-dimensional data sets and stereographic images from (for example) the surface of Mars, but due to recent release of 3D DVDs, they are increasingly used for entertainment. Anaglyph images are much easier to view than either parallel sighting or crossed eye stereograms, although the later types offer bright and accurate color rendering, which is not quite obtainable with even good color anaglyphs.

In general [by Admin]

Mon, 14 Aug 2006 01:26:54 +0200

Lenticular 3D:: In general
Lenticular means "biconvex". A single convex lens magnifies images.

A lenticular lens is an array of magnifying lenses, designed so that when viewed from slightly different angles, different images are magnified.

The simplest form of a lenticular lens is a bifocal, which has just two magnifying lenses.

Typically lenticular lenses are used to make lenticular print, for transforming, moving images, or 3d-effects.

Lenticular eyeglass lenses are employed to correct extreme hyperopia (farsightedness), a condition often created by cataract surgery when lens implants are not possible. To limit the great thickness and weight that such high-power lenses would otherwise require, all the power of the lens is concentrated in a small area in the center. In appearance, such a lens is often described as resembling a fried egg: a hemisphere atop a flat surface. The flat surface or "carrier lens" has little or no power and is there merely to fill up the rest of the eyeglass frame and to hold or "carry" the lenticular portion of the lens. This portion is typically 40mm in diameter but may be smaller, as little as 20mm, in sufficiently high powers. These lenses are generally used for plus (hyperopic) corrections at about 12 diopters or higher. A similar sort of eyeglass lens is the myodisc, sometimes termed a minus lenticular lens, used for very high negative (myopic) corrections.

Re: Virtual reality [by Admin]

Mon, 14 Aug 2006 00:55:55 +0200

General Information (Virtual Reality):: Virtual reality
The future

It is unclear exactly where the future of virtual reality is headed. In the short run, the graphics displayed in the HMD will soon reach a point of near realism. The aural aspect will move into a new realm of three dimensional sound. This refers to the addition of sound channels both above and below the individual. The virtual reality application of this future technology will most likely be in the form of over ear headphones.

With our technological limits today, sight and sound are the only two senses that will be able to be replicated almost flawlessly. In order to engage the other senses of touch, smell, and taste, the brain must be manipulated directly. This would move virtual reality into the realm of a vivid dream not dissimilar to "The Matrix". Although no form of this has been seriously developed at this point, Sony has taken the first step. On April 7th, 2005 Sony went public with the information that they had filed for and received a patent for the idea of the non-invasive beaming of different frequencies and patterns of ultrasonic waves directly into the brain to recreate all five senses. There has been research to show that this is possible. Sony has not conducted any tests as of yet and says that it is still only an idea.

LCD shutter glasses [by Admin]

Mon, 14 Aug 2006 00:47:34 +0200

LCD Shutter Glasses:: LCD shutter glasses
LCD shutter glasses are glasses used in conjunction with computers to create the illusion of a three dimensional image, an example of stereoscopy. Glass containing liquid crystal and a polarizing filter has the property that it becomes dark when voltage is applied, but otherwise is translucent. A pair of eyeglasses can be made using this material and connected to a computer video card. The video card alternately darkens over one eye, and then the other, in synchronization with the refresh rate of the monitor, while the monitor alternately displays different perspectives for each eye. This is called Alternate-frame sequencing. At sufficiently high refresh rates, the viewer's visual system does not notice the flickering, each eye receives a different image, and the effect is achieved.

The problems associated are the cost for the additional equipment (typically up to US$100), and that the flickering can be noticeable if the refresh rate is not sufficiently high, as each eye is effectively receiving only half of the monitor's actual refresh rate. As with other single image methods the brightness is considerably diminished.

Another possible effect is "ghosting". Since the opaque phase of the LC still permits a small amount of light to transmit, some users experience secondary "ghost" images from the alternate channel. This effect can be exacerbated by persistence effects in the phosphors of the CRT, causing images to "bleed" over into the other channel.

Until recently, the method only worked with CRT monitors; some modern flat-panel monitors now support high enough refresh rates to work with some LC shutter systems.

Stereoscopy [by Admin]

Mon, 14 Aug 2006 00:45:00 +0200

General Information (Stereo Photography):: Stereoscopy
Stereoscopy, stereoscopic imaging or 3-D (three-dimensional) imaging is any technique capable of recording three-dimensional visual information or creating the illusion of depth in an image. The illusion of depth in a photograph, movie, or other two-dimensional image is created by presenting a slightly different image to each eye. Many 3D displays use this method to convey images. It was first invented by Sir Charles Wheatstone in 1838. Stereoscopy is used in photogrammetry and also for entertainment through the production of stereograms. Stereoscopy is useful in viewing images rendered from large multi-dimensional data sets such as are produced by experimental data. Modern industrial three dimensional photography may use 3D scanners to detect and record 3 dimensional information.

Traditional stereoscopic photography consists of creating a 3-D illusion starting from a pair of 2-D images. The easiest way to create depth perception in the brain is to provide to the eyes of the viewer two different images, representing two perspectives of the same object, with a minor deviation similar to the perspectives that both eyes naturally receive in binocular vision.