This is no small feat, as any researcher who has tried to program a computer to understand images will tell you. The only way we can see that this is actually happening is to blow the dots up so big that our brains can no longer assemble them, like this:. Most people, sitting right up close to their computer screens , cannot tell what this is a picture of -- the dots are too big for your brain to handle.
If you stand 10 to 15 feet away from your monitor, however, your brain will be able to assemble the dots in the image and you will clearly see that it is the baby's face.
By standing at a distance, the dots become small enough for your brain to integrate them into a recognizable image. Both televisions and computer screens as well as newspaper and magazine photos rely on this fusion-of-small-colored-dots capability in the human brain to chop pictures up into thousands of individual elements.
On a TV or computer screen, the dots are called pixels. The resolution of your computer's screen might be x pixels, or maybe x pixels. The human brain's second amazing feature relating to television is this: If you divide a moving scene into a sequence of still pictures and show the still images in rapid succession , the brain will reassemble the still images into a single, moving scene.
Take, for example, these four frames from the example video:. Each one of these images is slightly different from the next. If you look carefully at the baby's left foot the foot that is visible , you will see that it is rising in these four frames. The toy also moves forward very slightly. By putting together 15 or more subtly different frames per second, the brain integrates them into a moving scene.
Fifteen per second is about the minimum possible -- any fewer than that and it looks jerky. When you download and watch the MPEG file offered at the beginning of this section, you see both of these processes at work simultaneously.
Your brain is fusing the dots of each image together to form still images and then fusing the separate still images together into a moving scene. Without these two capabilities, TV as we know it would not be possible.
A few TVs in use today rely on a device known as the cathode ray tube , or CRT , to display their images. LCDs and plasma displays are other common technologies. It is even possible to make a television screen out of thousands of ordinary watt light bulbs!
You may have seen something like this at an outdoor event like a football game. Let's start with the CRT, however. The terms anode and cathode are used in electronics as synonyms for positive and negative terminals. For example, you could refer to the positive terminal of a battery as the anode and the negative terminal as the cathode.
In a cathode ray tube, the "cathode" is a heated filament not unlike the filament in a normal light bulb.
The heated filament is in a vacuum created inside a glass "tube. Electrons are negative. The anode is positive, so it attracts the electrons pouring off the cathode. In a TV's cathode ray tube, the stream of electrons is focused by a focusing anode into a tight beam and then accelerated by an accelerating anode. This tight, high-speed beam of electrons flies through the vacuum in the tube and hits the flat screen at the other end of the tube.
This screen is coated with phosphor, which glows when struck by the beam. There is a cathode and a pair or more of anodes. There is the phosphor-coated screen. There is a conductive coating inside the tube to soak up the electrons that pile up at the screen-end of the tube. However, in this diagram you can see no way to "steer" the beam -- the beam will always land in a tiny dot right in the center of the screen. That's why, if you look inside any TV set, you will find that the tube is wrapped in coils of wires.
On the next page, you'll get a good view of steering coils. The steering coils are simply copper windings see How Electromagnets Work for details on coils. These coils are able to create magnetic fields inside the tube, and the electron beam responds to the fields. One set of coils creates a magnetic field that moves the electron beam vertically, while another set moves the beam horizontally. By controlling the voltages in the coils, you can position the electron beam at any point on the screen.
A phosphor is any material that, when exposed to radiation, emits visible light. The radiation might be ultraviolet light or a beam of electrons. Any fluorescent color is really a phosphor -- fluorescent colors absorb invisible ultraviolet light and emit visible light at a characteristic color. In a CRT, phosphor coats the inside of the screen.
When the electron beam strikes the phosphor, it makes the screen glow. In a black-and-white screen, there is one phosphor that glows white when struck. In a color screen, there are three phosphors arranged as dots or stripes that emit red, green and blue light.
There are also three electron beams to illuminate the three different colors together. There are thousands of different phosphors that have been formulated. They are characterized by their emission color and the length of time emission lasts after they are excited. In a black-and-white TV, the screen is coated with white phosphor and the electron beam "paints" an image onto the screen by moving the electron beam across the phosphor a line at a time.
To "paint" the entire screen, electronic circuits inside the TV use the magnetic coils to move the electron beam in a " raster scan " pattern across and down the screen.
The beam paints one line across the screen from left to right. It then quickly flies back to the left side, moves down slightly and paints another horizontal line, and so on down the screen.
In this figure, the blue lines represent lines that the electron beam is "painting" on the screen from left to right, while the red dashed lines represent the beam flying back to the left. When the beam reaches the right side of the bottom line, it has to move back to the upper left corner of the screen, as represented by the green line in the figure. When the beam is "painting," it is on, and when it is flying back, it is off so that it does not leave a trail on the screen.
The term horizontal retrace is used to refer to the beam moving back to the left at the end of each line, while the term vertical retrace refers to its movement from bottom to top. As the beam paints each line from left to right, the intensity of the beam is changed to create different shades of black, gray and white across the screen. Because the lines are spaced very closely together, your brain integrates them into a single image.
A TV screen normally has about lines visible from top to bottom. In the next section, you'll find out how the TV "paints" these lines on the screen.
Standard TVs use an interlacing technique when painting the screen. In the absence of Helmholtz coils, a strong neodymium magnet should suffice to bend the electron beam. The beams of electrons are too dim for anything except a very small audience to see directly, and are something of a challenge for video equipment too!
A camera with a night mode, or manual control over gain or ISO and shutter speed will probably be necessary. The key here is that magnetic fields will bend the path of a moving charged particle, and we can make use of this effect to control a beam. Crucially for the Accelerate! Some of these fast-moving electrons crash into the gas inside the tube, causing it to glow, which allows us to see the path of the beam. Helmholtz coils can then be used to apply a quantifiable magnetic field by passing a known current through them.
Download this image ». A magnetic field will cause a force to act on the electrons which is perpendicular to both their direction of travel and the magnetic field. That goes for shows, movies, and live sports and other events. And YouTube TV is smart about it. Most recordings extend 1 minute past their scheduled end time. Sporting events, by default, record an extra 30 minutes — and YouTube TV can even detect if things are going to run longer and extend things from there.
YouTube TV also allows for up to six user profiles on a single account. YouTube TV is tied to your Google account, and the profiles will be available for up to five other family members as designated in your Google account. Many of the channels included with a YouTube TV subscription let you watch their shows after they initially air, on-demand.
It can be a handy way to catch up on older episodes or seasons that aired before you started to record them using the DVR function. YouTube TV has a cool feature if you own a Google Home speaker, like the Google Nest Mini, and use a Chromecast device to watch YouTube TV: You can use just your voice to control functions like selecting a TV channel to watch live, starting specific shows, recording a show, or using playback functions such as pause, resume, and rewind. One of the greatest things about mobile video apps is the ability to watch via picture-in-picture.
It really is a game-changer. This feature lets you jump to various segments within select news programs on YouTube TV. This feature is available on TV apps now and will come to mobile devices soon. YouTube TV also is one of the only first live streaming services in the United States to offer some live content in 4K resolution. The other is FuboTV. You might get a lower resolution for a few seconds before the buffer fills out and hits max capacity.
And it all depends on the strength of your home network, and speed of your ISP, in addition to however YouTube TV and its content providers are offering the show or movie or sport in the first place.
There are a lot of moving parts here. Generally speaking, YouTube TV has as competitive a slate of channels — both linear and nonlinear that is, something other than what you might find on traditional cable TV — as any of the other comparable offerings.
0コメント