Archive for the ‘A quick peek behind the curtain’ Category
And here we go again on our trip to understanding the coolest technologies for 3D and Augmented Reality, and today’s subject will be, again, tracking. We have so much to say that the last article was nearly not enough. Before all, I would like to thank you for the feedback on these articles. And now, let’s go !
Actually, three of the things I’m going to talk about today are present in a single small object, and I’m talking about that :
I see Infrared waves
Did you know that the Nintedo Wiimote is equipped with one of the best infrared camera you can find on the market for this price? So you may wonder why there is an infrared camera, and maybe even what an infrared camera is… So let’s start from the beginning: The human eye can see colors. But what is a color? It’s an electromagnetic wave whose wavelength is between 400 nanometers and 800 nanometers. (1 nanometer is a billionth of a meter). Wavelength is linked to frequency (the lower the wavelength, the higher the frequency). Red has the lowest frequency of all colors, then, the order of colors follow the rainbow and finishes with violet. Frequencies above violet can’t be seen by the human eye. They include X rays and Gamma rays, and are called ultraviolet. Frequencies under red can’t be seen either. They include the waves use to listen to the radio, micro-wave from your oven, Wi-Fi and cell phone waves, and, as you have probably guessed, they are called infrared. But if the eye can’t see them, some kind of cameras can, it’s a normal source of light that can be seen. And this kind of camera is mounted at the front of your Wiimote. What is it starring at? The small device Nintendo called the “Sensor bar”, which is not a logical name, as it has no sensors in it. The sensor bar is composed of 2 infrared LEDs. When it sees them, it can measure the angle between them and the camera, thus deriving it’s position compared to the sensor bar.
A cool feature of infrared is that it is linked to heat. Whenever a body is producing heat, it will emit infrared waves, and your body is creating quite an amount of heat, so if you touch a flat surface that has an infrared camera on the other side, the camera will see an infrared point where you touch it. This can be used for multi-touch screens. The video below shows how to create a DIY touch screen with a normal computer, a wiimote and a few things.
Move with style !
Let’s continue with 2 other features in the Wiimote : the accelerometer and the gyroscope.
The universal gravitation law states that the Earth applies a force on everything that has a mass, pulling it toward our planet’s center, which is called gravitation. Newton’s law states that this force creates acceleration, going to the same direction. So if we measure the acceleration in 3 directions, we can find which one is “the direction to the center of the Earth” which is usually called “down”. So all we need is an accelerometer, and that’s good because accelerometer is easy to build. We simply use a piezoelectric material, like Quartz, which is a kind of material which generates an electric tension when a force is applied. And that’s it. Measure the tension, you have the force, measure the force in the 3 directions and you know where is “down”, so you know your orientation. Well not exactly, because you still miss some orientation information. And that’s where the gyroscope comes in handy. This small device is mainly a wheel that is rotating fast. And calculus says that the faster the wheel turns, the more difficult it will be to change its rotation axis, so you can have an object that will keep the same orientation even if the things it’s attached to turns. With the gyroscope and the accelerometer, you can have your complete orientation.
If you want to know more about the wiimote, you can try there.
And if you want to see the power of a gyroscope, watch that :
So there will be a part 3, for Computer Vision, the coolest of the coolest technology out there (in my humblest opinion). Stay tuned! Goodbye!
So we’re on for our second part exploring the three dimensional dreams of stereoscopy. Thank you for the feedbacks on the first part. Let’s dive into our subject.
Strange and new goggles
There are lots of different ways to get rid of the annoying color loss of the anaglyphs. One smart way is to pick 6 colors instead of 2: 2 shades of red (R1 & R2), 2 shades of green (G1 & G2) and two shades of blue (B1 & B2), that are different enough so that a filter that filters one does not filter the other. That way, we can translate our left image in R1G1B1 and the right image in R2G2B2, and then, we have our 3 dimensions with slightly no color loss.
But once we quit the Anaglyph system; there are a few techniques that are worth seeing. And to begin with, light polarization. You might know that light is the effect of electromagnetic waves. Or maybe you don’t know what electromagnetic waves are, and that’s not a problem, because you won’t need specific knowledge about it. All you need to know is those 3 facts: it oscillates (like the waves in the sea), we do know how to build filters (polarizing filters) to suppress the oscillations in specific directions, and when all the oscillation is suppressed, we don’t see anything. So here’s the plan: First, we take 2 video projectors, and they project the 2 films (left eyed and right eyed) on the same spot. One is polarized along a direction (let’s say horizontal), and the other one is polarized along a perpendicular direction (let’s say vertical). Then you wear specific glasses that have a horizontal filter or the right eye, and a vertical filter on the left eye. The horizontal filtered film can pass an horizontal filter again, so your right eye can see it, but when it comes to the vertical filter, it can’t pass through, because it would suppress all the oscillations. Thus, your right eye can only see the right eyed film and your left eye the left eyed one.
We can take this technique to a higher level : if you tilt your head 90°, your vertical filter becomes horizontal and vice versa, so instead of vertical and horizontal filters, we can use circular filters: one that turns clockwise, and the other counterclockwise. That way, even if you’re upside down, you can still see the right image. Keeping on getting better and better, video projectors (especially for cinema) are quite expansive, so there is a method to do it with only one projector : using a modulator that can polarize alternatively clockwise and counterclockwise give an electrical input. We just have to create alternative images from the left film with one polarization and the right film with the other polarization, and oscillate quickly between the images. And that’s how James Cameron’s Avatar works (see Real ID Cinema).
And at home ?
If you keep the “alternate the left and right image at high frequency” side and replace the polarization with electrostatic glasses that can cover alternatively one eye and the other, you get a good and simple way to have stereoscopy at home, given you have those glasses (let’s say Nvidia 3D Vision, 200$), a high frequency screen (at least 120 Hz if you want a neat image, keep in mind that it will be divided by 2) and you can have 3D at home and enjoy active stereoscopy!
Another solution is called auto-stereoscopy. Do you remember those cool mouse pads and fridge magnets that were so cool in the 90’s, there were 2 images on them, and depending on the direction you would watch, you would see one image or the other one. Imagine the same system mounted on a screen. Using lens, and splitting the screen into tiny vertical zones, we can make it so that if you’re right in front of the screen at the right distance, your left eye and right eye see different images. That way, we can throw the 2 films to the right eye. You want to try this out ? Check out the numerous Youtube video about the Nintendo 3DS announced at E3 2010 recently.
Hi. You may not know me yet, as I just joined 3D California. My name is Joachim, I’m a French intern and I’ll do my best to provide frequently some quality articles about Augmented Reality in this blog for all of you, 3D and AR fans.
So, after two or three years of hype, you sure know what Augmented Reality is. Or at least you have a lot of examples in mind. But AR is both the set of technologies and hardware, and what we do out of it. And we keep creating, discovering, and inventing new gadgets and new ways to use them.
As impressive as all these new applications can seem, there’s no such thing as magic. I’d like to take you on a tour to see a few tricks, explain a few technical points, and help you understand how it works, and this is the aim of the series of articles entitled “A quick peek behind the curtain” that I’ll be writing for you on the next weeks. I’m not (yet) a professional; I’m still learning lots of new things everyday and the content of these articles are the results of personal research, visits, discussions and a few years of great interest toward Augmented Reality, its technologies and applications, but it’s a fast moving world. So there might be a few points that are out-of-date, or not quite precise. Feel free to correct me if I’m wrong. Of course, I’ll do my best to document and source my articles, so that most of what I say can be checked.
Let’s lift that curtain a bit !
Today, I will talk about why the Cyclops from Homer’s Odysseus would not have appreciate James Cameron’s Avatar.
As a huge 3D fan, there’s nothing you appreciate more than this feeling of immersion given by the use of the three dimensions. Of course, today, we can do pretty neat things with a 3D artist and a normal TV or computer screen. And we can see those fantastic models rotate in every direction, just in front of us. But that’s nothing in comparison to what we feel when those models start turning around us. I’m sure that you felt something special when you saw that beast coming right behind your nose. All the trick comes from that obvious fact: unlike Homer’s Cyclops, we have two eyes.
And now for the explanation: our eyes are both able to see. But given that each of them is on one side of the nose (we estimate the distance between the eyes at about 65 millimeters or 2.56 inches), they don’t see exactly the same thing. For objects that are far away, there is no difference (try to watch through the window and close alternatively one eye and the other, and you should see about the same thing). But for objects that are close, this is a different matter (this time, hold a pen a few centimeters in front of you, and close your eyes alternatively again, watching you screen. Depending on which eye is open, the pen is on a completely different location). The left eye sees them on its right, and the right eye sees them on its left. And when the brain gets the 2 images, it’s able to figure out which objects are seen the same way by the two eyes (they are far away) and which objects are different (and thus closer) and estimate their distance.
That said, we still want to get that cool Avatar 3D effect, so… how do we do now? The answer holds in a few words: we simply film with 2 cameras that are distant of about 65 millimeters, and we get 2 different movies: a right eyed one and a left eyed one. And we just have to send the movie to the good eye. Easy to say, isn’t it? There are a few methods for targeting a specific eye with a specific movie, let’s see a few of them.
The anaglyphs :
I bet that you recognize those glasses from, let’s say, the last time you bought cereals. And the images to use with are like that. You know that the colors are combinations of Red, Green and Blue. And when you put a colored filter (like a colored glass or transparent plastic sheet), you only distinguish the other colors. So we keep the red part of the left image, and the blue + green (= cyan) part of the right image, join the 2 images and have you look at it through the glasses. Your left eye has the cyan filtered out, and only sees the red details, and vice versa. ” Et voilà!”. But this long known trick has a problem: you can’t really play with colors anymore, because you use them with stereoscopy.
They are a lot of others techniques that I’ll be explaining in more details next week, including the way Avatar’s 3D was done. Hope you liked that first article. Feel free to give us feedback, reactions, details or simple comments, so that it will get better and better with time!
Have a good week!
Bonus: if you have anaglyph glasses, you can feel again that 3D feeling with the trailer of Avatar in anaglyph 3D
Internet source :
Different website, but all the informations also appear on the Wikipedia article