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Thread: Guides & Tutorials

  1. #21
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    Default TUTORIAL: possible fix for computer freezing or rebooting at

    Problem:

    Computer freezes or reboots at random intervals.


    Possible fixes:

    Update Windows. Ensure you have the latest service packs installed.

    Update all Device drivers. Driver issues, especially for video drivers, are a common cause of system crashes.
    Scan for viruses, malware, spyware. Click here for a complete list of free utilities that will perform a thorough scan of your system.

    Re-seat all cards & plugs.

    Test your RAM. Use this utility, and let it run overnight for best results.

    Test your HDD. Click Start --> My Computer. Right-click the disk you want to check (usually C: ). Select Properties. Click on the Tools tab. Under Error Checking, click Check Now. Select the Automatically Fix File System Errors option, and the Scan For and Attempt Recovery of Bad Sectors option. Click on Start.

    Defragment your hard drive(s). Click Start --> All Programs --> Accessories --> System Tools --> Disk Defragmenter.

    Confirm that system temperatures are not reaching critical levels. Processors are especially susceptible to overheating, but other components can also cause problems.Consult the forums for diagnostic tools that will analyze your system temperatures.


    Ensure your power supply is adequate to the needs of your system. If you have purchased a bare bones system to save a few bucks, and have added components over time (drives, video cards, etc.), these add-ons may be making demands that your power supply is unable to handle. Determine the wattage rating on the power supply in your machine; the label on it will usually provide this information. Then click on this link to calculate your system's requirements.


    Try to recall any changes you have made to your system. New hardware or software will sometimes cause conflicts, creating problems where none previously existed. If you begin having issues and can pinpoint their occurrences to a time immediately after a change was made to your system, the new hardware/software may be the problem.

    Clean the registry. A Google search will direct you to several free utilities that will scan and clean your registry.

  2. #22
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    Default Guide:How To Remotely Access Your Pc

    Windows XP Professional includes a basic PC remote control tool which lets you log onto your PC remotely from anywhere. Do you know how to use it


    It’s called Remote Desktop Connection, and when you’ve properly configured your PC, this handy utility will let you log into your computer from anywhere in the world and control it as if you were sitting in front of it instead of half a world away.

    If you’re running Windows XP Professional, you already have all the software you need to connect remotely to your PC. Whether you’d like to monitor a server, grab files from your home PC at work, or just keep an eye on your machines when you’re out, connecting remotely is easy to do. However, due to the vagaries of network configurations and various other quirks beyond your control, you may not be able to actually connect. Until now.



    Prepping your system

    First, you need to know the IP address of the computer you want to connect to. The only sure-fire way to always be able to connect to your PC’s is to use an ISP that provides you with a static IP address. Most ISPs give customers dynamic IP addresses, which can change every few days or even hours. Because your IP address is the way you’ll locate your computer on the net, you’ll need to know what your IP address is and monitor it as it changes.

    The good news is that there are loads of programs that will notify you of IP address changes, whenever they occur. We like IP Address Monster (www.ipmonster.com). It’s a small program that runs in your system tray and can be configured to e-mail you whenever your IP address changes.




    IP Address Monster should be your first stop to remote connectivity. This handy utility will keep tabs on your Internet address and send you an e-mail whenever it changes.



    Now that you know your IP address, you need to make sure that Remote Desktop Connection is enabled. Make sure your firewall is configured to allow incoming connections on port 3389 (firewalls vary, so check your documentation to find out how to open the port).

    You can turn on Remote Desktop Connection in the System Control Panel (Start, Control Panel, System). Check the Remote tab and make sure “Allow users to connect remotely to this computer” is checked. You’ll also need to have at least one user account that requires a password because accounts without passwords are prohibited from logging into Remote Desktop.





    To enabling Remote Desktop, open the System Control Panel, go to the Remote tab, and check this box.



    It’s important to make sure the passwords on the machine you’re going to remotely log into are “good” ones. This means you should use a mixture of letters and numbers, avoid words that are found in dictionaries, and change the password regularly to protect yourself from mischief.



    Making the connection

    At this point, your PC should be prepped and patiently waiting for a connection. To log in, you need to open the Remote Desktop Connection client on your remote PC. Go to Start, Programs, Accessories, Communications, Remote Desktop Connection. Input the IP address you want to connect to (courtesy of IP Address Monster) in the Computer field. Then enter your username and password.

    Now you’ll want to tweak a few settings to optimize your remote experience. Whiz-bang features gobble up bandwidth, so you should tune your settings to match your home net connection. We recommend you start with a minimal feature set. Press the Options button, then the Display tab. Change the display settings to full-screen, 256-color. This looks acceptable and consumes practically no bandwidth. You’ll also want to browse to the Experience tab and change the Performance setting to reflect your home PC’s connection speed.




    Switching to a lower color resolution and a smaller display area will greatly minimize the amount of data that has to transfer between your computer and the remote PC.



    Once you’ve tuned the connection a bit, you’re ready to connect. Press the Connect key and you’re in!



    What to do next

    At this point, you should be connected. You can run programs and manipulate files just like you’re sitting in front of your PC. In fact, you can even use your PC’s e-mail and web browsers. Do you want to start downloading Desert Combat now so you can start playing it when you get home That’s easy enough; just log into your PC using Remote Desktop, open your web browser, and download the file. It will be sitting on your machine waiting for you as soon as you get home. If all your PCs are running Windows XP Pro, and you enable drive-sharing in the Local Resources tab, you can transfer files from remote PC to local PC. You can even remotely transfer files between local PCs on your home network.


    Once connected, you can interact with printer ports and networked hard drives. This is a handy way to delete those “special interest” videos you downloaded before your wife finds them.

  3. #23
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    Default Google Earth: Planetary Phenomenon

    Google Earth: Planetary Phenomenon

    From its exit in August 2005, Google Earth became a true phenomenon. The receipt of its success? A brilliant concept (even if it is not new as we will see it) and an impeccable technical realization. The goal of the software? To provide an urban and geographical guide total, based on a representation 3d detailed and realistic of the Earth. In theory, Google Earth makes it possible to seek imports what on our beautiful planet: a pizzeria, a historic building, a route of its hotel to the cinema nearest. The software posts a level of detail such as one can even have access to a modeling 3d (simple) of the buildings over the detailed satellite images, themselves and taking account of the relief. Sum colossal of information is diffused in "streaming" since Internet (even if the images satellite can go back to a few years), in short, Google Earth is a mine of information on our planet, constantly updated.

    In practice, unfortunately, all that relates to currently only the United States: the buildings are reserved for 38 cities American and only some European cities have a level of high detail and information practical. Would Google Earth be thus a simple gadget with the interest limited for the remainder of planet? Certainly not! The force of the software is indeed to make it possible to the Net surfers to add their own information. Simple "bug" on the sphere with modeling 3d of a monument or a building, it is thus possible to personalize Google Earth with its own way and to benefit from innumerable information brought by a very active community.




    Earth with range of mouse: To discover Google Earth

    Let us start with the beginning, namely the remote loading of the software. Google Earth exists in several versions. The paying versions propose additional functionalities like the possibility of adding buildings in 3d or functions related to the GPS, but the free version is obviously sufficient to explore the Earth under all its seams. Google Earth is available under Windows and Mac OS X (10.3 minimum)

    Before launching us to the research of the villa of Zidane or desert of Tatooine, we with the interface of the software, broken up into three parts familiarize already:

    The principal window.
    The panel of navigation.
    The side panel.

    Navigation in Google Earth can be made several manners. Most intuitive is "to handle" the ground with the mouse, a method which uses all the buttons.

    The left button enables you "to catch" the terrestrial sphere and to turn it in all the directions.
    The right button allows zoomer ahead or behind, but it is much more practical to carry out this handling with the serrated roller of the mouse which lends itself to it to wonder.
    Lastly, the central button makes it possible to modify the slope and to swivel of left on the right.



    Short cuts keyboard are also available:
    + and - for zoomer ahead and behind.
    Pg Up and Pg Down to modify the slope.

    Lastly, you can use the panel of navigation which gathers the same functions:

    Central paving stone to turn around the sphere.
    The buttons left and right-hand side to carry out a rotation on the left or on the right.
    The small rule of left for zoomer ahead and behind.
    The small rule of right-hand side to modify the slope.



    Let us note then the presence of three buttons in bottom on the right of the interface to print a sight, to send it by electronic mail, or to add information in the form of a simple marker, a superimposed image or a modeling in 3d (this last option being reserved for Google Earth Plus, paying). We will reconsider this function later.

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    The side panel, multi-fonction pocket knife of the "Google-earthien"

    These possibilities of navigations already make it possible to have fun with the sphere and of zoomer on more detailed places (of the zones generally delimited by squares of color chestnut) to be filled with wonder at the level of precision of certain agglomerations. If you live Paris, Marseilles, Lyon, Strasbourg or Bordeaux, you will not have undoubtedly evil to find your house.



    Nevertheless, the essence of Google Earth is in the side panel. That Ci is divided into three parts.

    The module of research

    This one comprises three mitres "Fly to" makes it possible "to fly" towards a specific place by seizing the name. It goes without saying that during the first minutes of use of the software, it is one of the jouissives functionalities: what a pleasure "of leaping" from Paris in New York, Rio or Peking in a few seconds! "Local Search", as its name indicates it, consists in seeking a trade or a monument in a city. Lastly, "Directions" makes it possible to calculate a route between two points. The last two mitres are more or less reserved for the American public.

    The module "Places"

    This module is the equivalent of the bookmarks in a navigator. You can safeguard your places preferred there to reach it later on of a simple double clic. It is also in this panel that the places added with the files added by the users are stored.

    To exploit this module, one uses the button of the panel of navigation. A clic on this button opens a menu proposing to you to add a marker ("placemark"). You can also add other types of information as more precise charts which are superimposed on those provided by defect, or even of the models 3d of buildings or monuments, but this requires jurisdiction which exceed this article. We will however see some very successful examples of these additions.

    To add a "placemark" is as simple as to add a bookmark to your navigator. You can use the button bug and choose "placemark", use the short cut Ctrl+N keyboard or, in the panel "Places", carry out a clic right and choose New > Placemark. A dialog box opens, in which you can name your marker, to assign another icon to him or to place it in an existing file (or to create new).

    Note the buttons of reading in bottom of the module. Those enable you to carry out a turn of the world of your markers. To give an account of their interest to you, launch the turn of the places available by defect: campus of Google to the Imperial Palate of Tokyo while passing by Berlin or Peking, there is what to return jealous Jules Verne!

    The module "Layers"

    It makes it possible to post or mask a great number of copies on the sphere (borders, reliefs, buildings in 3d, roads, trade, schools, churches...) by notching them. The principal copies (real, reliefs, roads, lodging, restoration, borders) are also accessible since the panel from navigation.

    This system of check box also functions in the panel "Places", from where interest to create files sets of themes where to arrange your favorite places. By notching or stripping the file, you will be able thus to post or hide all the markers who are there.




    A software in perpetual motion

    Several types of information can be added to Google Earth. These additions can be simple markers posed on an existing place (a subway station, a monument, a building...), but also the superposition of an image over the information provided by defect, like a more precise air sight of a city. For most senior, it is also possible to add models in 3d of monuments or buildings. The addition of information and in particular of modelings or charts is a relatively complex subject which exceeds the framework of this article. We nevertheless will teach you how to benefit from this richness from information.

    As we saw previously, it is possible to define markers in precise places. It is also possible to safeguard these markers in the shape of a file KMZ which could be carried out by any user of the software, the place being then automatically added to the panel "Places".

    The Community Google Earth
    The first level of personalization is provided by the community Google Earth. The software indeed places at the disposal a forum where find impassioned virtual sphere.


    The places added by the members of the community are classified and integrated every month into Google Earth. You can reach it by notching Google Earth community in the panel "Layers". By unfolding small Google Earth Community, you will notice that the places themselves are classified in various categories: travel information, transportation, nature & geography...

    An example? Turn over on our good France old woman and zoomez on Paris. You ensure that the category Google Earth Community is stripped and unfold it. Now, notch "Transportation": the subway stations of the capital appear. Strip this option and notch "Education now" and you will see appearing the Sorbonne and Sciences Po.



    The other information, considered to be less interesting by the community, is stored in the subcategory "Unranked". You can nevertheless find there information rather amusing. Always on Paris, a Net surfer indicated several places where a short film of Claude Lelouch was turned, another famous Café of the Two Mills of Amélie Poulain. Let us benefit from this example to use another functionality of the software: its integrated navigator. When you click on a marker, this one posts a bubble of information which can contain a bond towards the subject of the Community forum or an external site bringing more information, for example on a monument. A panel emerges then, allowing you of surfer on this site inside even of Google Earth. The software exploits engine Internet then To explore.

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    A little tourism

    We saw it, Google Earth allows to post modelings 3d of buildings over the satellite charts. Nevertheless, this functionality relates to currently only 38 American cities. Fortunately, of many buildings 3d, created by the users with third software like SketchUp (repurchased since by Google), can be downloaded on many blogs. Here a selection of modelled monuments. To visualize them, ensure you to have notched the category "Buildings" in the panel "Layers" or the panel of navigation.

    The Eiffel Tower

    Paris has a sight relatively detailed in Google Earth, but the Eiffel tower seems to have been crushed on the ground. This file gives again all its splendour to him, at the point to even put at knees the most modest configurations.



    Colisee


    Vestige emblematic of the Roman Empire, Colisée of Rome east reproduces in a rather faithful way with this model.



    Hollywood

    The famous letters of the hill of Hollywood overhang Los Angeles. Have fun with the camera, the vertiginous sight on the town of Los Angeles is impressive.



    The guide of the celebrities

    The "people" are with the honor on Google Earth. Human curiosity being what it is, temptation to fly over the properties of the stars of Hollywood or the personalities of this world is large. Among the multitude of markers available on the site Sauce Ketchup , we can thus steal such Tom Thumb of the villa of Zinédine Zidane to Madrid to the property of Bill Gates to Seattle while passing by the house of impossible to circumvent Tom Cruise... Unless you did not prefer David Hasseloff (the drafting declines any responsibility on the use of these bonds). These files are simple markers, you will not be able to thus visualize the properties under all their seams.






    One finds some places of turning (even of pilgrimage for the fans): the desert of Tatooine, in the first Wars Star, was turned to Tunisia, but also to Arizona, at the place of this marker.



    Peter Jackson put a point of honor to turn the entirety of the Lord of the Rings in his native New Zealand. Many places of turning, the volcano used to represent the Mountain of the Destiny, where Frodon must throw the single ring, is undoubtedly one of most impressive.



    Lastly, magic of Google Earth and the cinema (sic), we finish this turn of the world express train by the gendarmerie of Saint-Tropez, to return visit in Cruchot, Gerber and the others. Is that worth the Earth of the Medium well, not?

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    NASA World Wind: Another manner of scanning the Earth

    Google Earth, even if its quality is undeniable, is not the only free virtual terrestrial sphere. Its "competitor" is called NASA World Wind and even if it shows a light delay on certain points vis-a-vis Google Earth, it is far from being uninteresting and has some specific qualities, in particular a more scientific approach. On the other hand, contrary to Google Earth, NASA Worldwind does not have vocation to be a total urban guide allowing to find its way or the pizzeria nearest. Contrary to Google Earth, it is of more available only for Windows.



    The interface of NASA World Wind is rather different from that of Google Earth: one does not find panels multiple, but a bar of icons in top of the window. It gives access quickly the posting (or not) of the multiple layers of information suggested by the software: satellite images, charts topographic, meridian, borders, flags of the countries or monuments.



    As for Google Earth, the most detailed information and sights relate to only the United States, in particular the sight USGS Urban Area which provides very precise representations of the urban zones (but in black and white and without building in 3d contrary with Google Earth). Returned relief is comparable so that Google Earth proposes. The management of the relief is effective for the mountains, but NASA World Wind has the annoying tendency to plate an artificial relief on the cities, which causes somewhat hazardous results.

    Europe is even more badly parcelled out in World Wind and it is useless to seek there such precise sights of large French cities. Even Paris is much less detailed there.

    The volcano of theSaint-Helene Mount with NASA World Wind



    The volcano of theSaint-Helene Mount with Google Earth



    Which is then the interest of NASA World Wind compared to Google Earth, more especially as it is definitely bulkier? The answer lies in the excellent module Scientific Visualisation Studio.

    This module, accessible since a pressure on the F1 key, gives access to you many animations which are superimposed on the surface of the sphere. Those Ci describe scientific phenomena classified by categories: climatic changes, natural disasters, evolution of the vegetation... Each animation is accompanied by a description (in English) of the phenomenon. Google Earth, through the many files made available by the community, also proposes a certain number of animations of this type, but they are not centralized in a module of the software, which concentrates rather on practical information.

    Another interesting possibility of NASA World Wind, in addition to the Earth, the software also proposes a visualization 3d of the Moon. Google proposes these charts in the form of service Web, but not of three-dimensional version.

    With final, the two software is relatively complementary. NASA World Wind is ended a little less graphically and does not have the dynamic community of Google Earth, but it remains a very good tool.

    Services Web: Earth since its navigator

    Google Earth or NASA World Wind has beautiful being of the applications of quality, they require a relatively powerful configuration all the same to function in a fluid way. The more modest users of machines can nevertheless turn to services Web proposing of the functionalities similar, but based on cards in 2d.

    Google is obviously present in this field with Google Local (in the past Google Maps) which uses the same satellite images as Google Earth. Unfortunately, just like Google Earth, the service has of real interest only for the Americans, the aspect "guides proximity" being completely ineffective for the other countries, of which ours. Useless thus to seek a pizzeria in Bordeaux or Marseilles. On the other hand, not of problems for New-yorkais.

    The war that Google and Microsoft are delivered on the Web obviously led this last to propose its own alternative to Google Local, Windows Live Local . As for Local Google, it is based at the same time on charts and images satellite, resulting from NASA.

    The service proposes rather interesting functionalities. By taking again our search for pizzeria on New York, the service allowed us zoomer until an air sight of the street of the required pizzeria! For us other French, Windows Live Local is on the other hand of an interest even more limited, the French cities, including Paris, being locked on a level of very insufficient zoom.

    Microsoft also gives access to beta of an interesting technology which consists in exploring a city through a series of multiple photographs in subjective sight, in particular effective to represent a route visually.

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    Future for the Services

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    Which future for the services of cartography?

    We are clearly with the stammerings of the type of applications suggested by Google Earth or NASA World Wind. Already very impressive, those must nevertheless make with some limitations: whatever the software used, it always arrives a moment when the sight becomes fuzzy. Google Earth proposes its sight "buildings", but one begins to dream of modelings even more detailed of the streets. This progress themselves is limited by the colossal task that the virtualisation of our planet represents and inevitably influenced by their geographical origin. For the moment, the two software headlight is American. Google Earth has a very significant Community support which largely helps to fill the international gaps of the software. Multiple projects are born: the near total of Germany thus has been just covered in high resolution and a project of modeling of the streets of London is in hand. Nevertheless, the software takes all its direction only if one lives in the United States or that one projects to go there. In the state, the "local" side of this type of services is still far from being exploitable for other countries.

    The most promising initiative remains "Google Earth French" promised by the IGN. Few information still filtered on this project, which should be partially paying, but it should restore a certain balance and to reach a level of detail without precedent of our territory the IGN thus promises a precision of a pixel for 50 cm thanks to photographs taken during mission of overflight in the plane. 400.000 stereotypes would be thus used to cover the hexagon and the DOM supplemented by 3600 charts sets of themes on the scale (excursions, river, drills, parks...). Partners as the Land register could them also bring their data. A video first of demonstration of the service is available since the blog of Jean Michel Billaut


    While waiting, Google Earth remains currently the most advanced application in its kind and the "total" dimension of the software is as for it a mine of information on our planet. Good explorations!

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    Complete Video Compression Guide

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    Complete Video Compression Guide

    We will start with basic discussions of analog and digital video, continues with the principles of video compression, and concludes with a description of three compression methods designed specifically for video, namely MPEG-1, MPEG-4, and H.261.


    Analog Video

    An analog video camera converts the image it “sees” through its lens to an electric voltage (a signal) that varies with time according to the intensity and color of the light emitted from the different image parts. Such a signal is called analog, since it is analogous (proportional) to the light intensity. The best way to understand this signal is to see how a television receiver responds to it.


    The CRT

    A television receiver (a CRT, or cathode ray tube), is a glass tube with a familiar shape. In the back it has an electron gun (the cathode) that emits a stream of electrons. Its front surface is positively charged, so it attracts the electrons (which have a negative electric charge). The front is coated with a phosphor compound that converts the kinetic energy of the electrons hitting it to light. The flash of light only lasts a fraction of a second, so in order to get a constant display, the picture has to be refreshed several times a second. The actual refresh rate depends on the persistence of the compound . For certain types of work, such as architectural drawing, long persistence is acceptable. For animation, short persistence is a must.

    The early pioneers of motion pictures found, after much experimentation, that the minimum refresh rate required for smooth animation is 15 pictures (or frames) per second (fps), so they adopted 16 fps as the refresh rate for their cameras and projectors. However, when movies began to show fast action (such as in westerns), the motion pictures industry decided to increased the refresh rate to 24 fps, a rate that is used to this day. At a certain point it was discovered that this rate can artificially be doubled, to 48 fps (which produces smoother animation), by projecting each frame twice. This is done by employing a double-blade rotating shutter in the movie projector. The shutter exposes a picture, covers it, and exposes it again, all in 1/24 of a second, thereby achieving an effective refresh rate of 48 fps. Modern movie projectors have very bright lamps and can even use a triple-blade shutter, for an effective refresh rate of 72 fps.

    The frequency of electric current in Europe is 50 Hz, so television standards used there, such as PAL and SECAM, employ a refresh rate of 25 fps. This is convenient for transmitting a movie on television. The movie, which was filmed at 24 fps, is shown at 25 fps, an undetectable difference. The frequency of electric current in the United States is 60 Hz, so when television came, in the 1930s, it used a refresh rate of 30 fps. When color was added, in 1953, that rate was decreased by 1%, to 29.97 fps, because of the need for precise separation of the video and audio signal carriers. Because of interlacing, a complete television picture is made of two frames, so a refresh rate of 29.97 pictures per second requires a rate of 59.94 frames per second. It turns out that the refresh rate for television should be higher than the rate for movies. A movie is normally watched in darkness, whereas television is watched in a lighted room, and human vision is more sensitive to flicker under conditions of bright illumination. This is why 30 (or 29.97) fps is better than 25. The electron beam can be turned off and on very rapidly. It can also be deflected horizontally and vertically by two pairs (X and Y) of electrodes. Displaying a single point on the screen is done by turning the beam off, moving it to the part of the screen where the point should appear, and turning it on. This is done by special hardware in response to the analog signal received by the television set. The signal instructs the hardware to turn the beam off, move it to the top-left corner of the screen, turn it on, and sweep a horizontal line on the screen. While the beam is swept horizontally along the top scan line, the analog signal is used to adjust the beam’s intensity according to the image parts being displayed. At the end of the first scan line, the signal instructs the television hardware to turn the beam off, move it back and slightly down, to the start of the third (not the second) scan line, turn it on, and sweep that line. Moving the beam to the start of the next scan line is known as a retrace. The time it takes to retrace is the horizontal blanking time.

    This way, one field of the picture is created on the screen line by line, using just the odd-numbered scan lines. At the end of the last line, the signal contains instructions for a frame retrace. This turns the beam off and moves it to the start of the next field (the second scan line) to scan the field of even-numbered scan lines. The time it takes to do the vertical retrace is the vertical blanking time. The picture is therefore created in two fields that together make a frame. The picture is said to be interlaced. This process is repeated several times each second, to refresh the picture. This order of scanning (left to right, top to bottom, with or without interlacing) is called raster scan. The word raster is derived from the Latin rastrum, meaning rake, since this scan is done in a pattern similar to that left by a rake on a field. A consumer television set uses one of three international standards. The standard used in the United States is called NTSC (National Television Standards Committee), although the new digital standard is fast becoming popular. NTSC specifies a television transmission of 525 lines (today, this would be 29 = 512 lines, but since television was developed before the advent of computers with their preference for binary numbers, the NTSC standard has nothing to do with powers of two). Because of vertical blanking, however, only 483 lines are visible on the screen. Since the aspect ratio (width/height) of a television screen is 4:3, each line has a size of 4/3 of 483 = 644 pixels.
    The resolution of a standard television set is thus 483×644. This may be considered at best medium resolution. (This is the reason why text is so hard to read on a standard television.)The aspect ratio of 4:3 was selected by Thomas Edison when he built the first movie cameras and projectors, and was adopted by early television in the 1930s. In the 1950s, after many tests on viewers, the movie industry decided that people prefer larger aspect ratios and started making wide-screen movies, with aspect ratios of 1.85 or higher. Influenced by that, the developers of digital video opted for the large aspect ratio of 16:9.

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    Composite and Components Video

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    Composite and Components Video


    The common television receiver found in many homes receives from the transmitter a composite signal, where the luminance and chrominance components [Salomon 99] are multiplexed. This type of signal was designed in the early 1950s, when color was added to television transmissions. The basic black-and-white signal becomes the luminance (Y ) component, and two chrominance components C1 and C2 are added. Those can be U and V , Cb and Cr, I and Q, or any other chrominance components. Figure 6.5a shows the main components of a transmitter and a receiver using a composite signal. The main point is that only one signal is needed. If the signal is sent on the air, only one frequency is needed. If it is sent on a cable, only one cable is used.

    Composite video is cheap but has problems such as cross-luminance and crosschrominance artifacts in the displayed image. High-quality video systems normally use component video, where three cables or three frequencies carry the individual color components (Figure 6.5b). A common component video standard is the ITU-R recommendation 601, which uses the YCbCr color space (page 626). In this standard, the luminance Y has values in the range [16, 235], whereas each of the two chrominance components has values in the range [16, 240] centered at 128, which indicates zero chrominance.

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    Digital Video

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    Digital Video



    Digital video is the case where the original image is generated, in the camera, in the form of pixels. When reading this, we may intuitively feel that an image produced this way is inferior to an analog image. An analog image seems to have infinite resolution, whereas a digital image has a fixed, finite resolution that cannot be increased without loss of image quality. In practice, however, the high resolution of analog images is not an advantage, since we view them on a television screen or a computer monitor in a certain, fixed resolution. Digital video, on the other hand, has the following important advantages:

    1. It can be easily edited. This makes it possible to produce special effects. Computergenerated images, such as spaceships or cartoon characters, can be combined with reallife action to produce complex, realistic-looking effects. The images of an actor in a movie can be edited to make him look young at the beginning and old later. Editing software for digital video is already available for most computer platforms. Users can edit a video file and attach it to an email message, thus creating vmail. Multimedia applications, where text, sound, still images, and video are integrated, are common today and involve editing video.

    2. It can be stored on any digital medium, such as hard disks, removable cartridges, CD-ROMs, or DVDs. An error-correcting code can be added, if needed, for increased reliability. This makes it possible to duplicate a long movie or transmit it between computers without loss of quality (in fact, without a single bit getting corrupted). In contrast, analog video is typically stored on tape, each copy is slightly inferior to the original, and the medium is subject to wear.

    3. It can be compressed. This allows for more storage (when video is stored on a digital medium) and also for fast transmission. Sending compressed video between computers makes video telephony possible, which, in turn, makes video conferencing possible. Transmitting compressed video also makes it possible to increase the capacity of television cables and thus add channels. Digital video is, in principle, a sequence of images, called frames, displayed at a certain frame rate (so many frames per second, or fps) to create the illusion of animation. This rate, as well as the image size and pixel depth, depend heavily on the application. Surveillance cameras, for example, use the very low frame rate of five fps, while HDTV displays 25 fps.

    Even the most economic application, a surveillance camera, generates 5×640×480×12 = 18,432,000 bits per second! This is equivalent to more than 2.3 million bytes per second, and this information has to be saved for at least a few days before it can be deleted. Most video applications also involve sound. It is part of the overall video data and has to be compressed with the video image. There are few video applications do not include sound. Three common examples are: (1) Surveillance camera, (2) an old, silent movie being restored and converted from film to video, and (3) a video presentation taken underwater. A complete piece of video is sometimes called a presentation. It consists of a number of acts, where each act is broken down into several scenes. A scene is made of several shots or sequences of action, each a succession of frames, where there is a small change in scene and camera position between consecutive frames. The hierarchy is thus piece- act- scene- sequence- frame.

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