Tutorial: How to save your Linux screen space
You probably already know that a tiling window manager is one of the alternatives often provided by distributions alongside the standard Gnome or KDE desktops. Instead of floating windows, with their ability to move anywhere, and stacked applications that overlap one another, a tiling window manager locks applications to the display, splitting as necessary to run applications side by side. When you run enough applications together, your desktop can start to look like a tiled bathroom, which is presumably why they're called tiling window managers.
But tiling managers can offer some genuine advantages over their more flexible rivals. A single application should run full-screen by default, for example, removing many of the distractions that can make a simple job last four times as long, and any applications you want to run at the same time are always visible.
There won't be any overlapping windows, unless you explicitly want them, and you don't have the distraction of playing with window borders.
If you're running a lower-resolution display, you'll make more effective use of your screen real estate by not having dead space. If you've got a high-resolution display, then you'll always be able to see the entire contents of the applications you're running, which is ideal if you're making notes or need a web browser open while you enter text into a document.
But making the transition from a regular window manager to the restrictions of a tiling window manager isn't easy. It can require a reprogramming of both your muscle memory and the way you think about your desktop.
We'll tackle both of these problems in this article, taking you deeper into the world of window managers and into the world of tiles.
KDE's hidden gem
It might be surprising, but a good place to start is with a desktop you're already used to, and the best choice is KDE. Starting with version 4.4, KDE took some tentative steps towards supporting tiling by enabling windows to dock next to one another, side-by-side.
Version 4.5 saw the idea through to its conclusion, adding a fully featured tiling mode that can turn your floaty KDE desktop into a strict matrix of windows.
These developments were presumably to help with the production of KDE's netbook interface, where applications will typically run as full-screen, and you need to make best possible use of the display. But it means that KDE 4.5 can now be turned into a useful tiling window manager.
As with most things in KDE, the option to enable tiling is hidden within several layers of configuration panels.
You can get to the option either from the title bar of an application or by opening the System Settings application, selecting Workspace Behaviour, switching to the Window Behaviour page and choosing Advanced. There's a large tick-box here that will turn off floating windows and enable window locking.
There are a few other options that can be used to fine-tune your experience. In the default layout of Spiral, for example, each new window will split the full-screen view clockwise. The first application will occupy the entire screen, while the second will appear on the right half.
Further applications will halve the lower quarter of the right half, and so on, until your display looks like a spiral of windows. The alternative is the two-column layout, as configured by choosing Columns, but we had problems getting consistent results with it.
Now that tiling is enabled, you can get a good idea of what a dedicated tiling window manager would feel like. You need to get used to a web browser filling the entire screen, for example, which can be a little disconcerting if the page you're viewing appears as a wide column. The biggest difference is with windows you usually leave floating, such as notifications, a Twitter client or instant messenger.
By default, KDE's window manager will force these to run full-screen, leaving you with a lot of blank space. The solution is to change how they appear from the floating window menu, which gives you some control on the amount of space they take up.
If you're looking for real control, you'll need to switch from KDE to a window manager designed to hand the power to you.
Tiling window managers are all about speed, and the quickest way to tell your computer what you want it to do is from the keyboard, since it's where your fingers are already resting. This is the primary motivation behind Ratpoison, a popular tiling window manager that hopes to convince you that your mouse is dead.
However, keyboard shortcuts need you to put in some effort before you actually start saving time using them, rather than running through the documentation. And most users will agree, Ratpoison has a steep learning curve.
You even need to prove you're up to the task before you can enter the environment – at least you do if you're running Ubuntu with the GDM login manager.
After installing the Ratpoison package, you'll need to either run the window manager manually or create a 'ratpoison.desktop' file in the ''/usr/share/xsessions' directory by copying the Xterm example and changing the executable path to '/usr/bin/ratpoison' and the 'X-Ubuntu-Gettext-Domain' to 'ratpoison-session'.
After that, you'll be able to see the new option in the login window manager menu.
But you won't see anything. Ratpoison is probably the most zen-like desktop for Linux, and doesn't clutter the screen with anything that suggests it's running. You might notice a brief message telling you how to get started, but if you happen to be checking your watch at that moment, Ratpoison will look exactly like a crashed desktop – a completely empty X server.
To get from this point to usability requires keyboard shortcuts, and the bit of information you've just missed is how to see a list of the keyboard commands.
Keyboard shortcuts
The most used shortcut in Ratpoison is Ctrl+T. This places the desktop into a mode ready to accept further keyboard commands. You could add the '?' key, for instance, to reveal the help file listing all the other keyboard shortcuts you can use, but here's our pick of the most useful ones.
Following Ctrl+T with 'C' will open a terminal, and from there you can launch any other applications you need. You can also replace 'C' with '!' to run a single command line.
Applications will run in full-screen mode, and they won't have any window border, meaning you can't move them with your mouse. Instead, you can use the 'N' (next) and 'P' (previous) shortcuts to switch between your running applications, although you'll also find this switches between tabs in Firefox too.
You can see which windows are open with 'W', and they'll be listed in what Ratpoison calls its status bar, which defaults to the top-right of the screen. Switch between windows and tabs by using the number that appears in the list.
All this keyboard speed might seem like an advantage, but there's currently very little tiling. At the moment, each application is running full-screen. This can be remedied with another shortcut, 'S', which will split the display horizontally, or Shift+S vertically.
The application behind the current one will then fill the space, and you can continue splitting the display in this way until you've got as many viewable applications within each section as you need. You can then switch between each section using the cursor keys, and you can resize the selected frame using 'R' followed by some judicious use of the cursor keys to expand and contract the application borders.
All the other frames will scale automatically to accommodate your changes, and and when you want to remove a frame completely from the display, use the 'Q' shortcut.
Custom config
Finally, if you really want to customise how Ratpoison handles applications, you'll need to edit the configuration file, which can be found hidden in your home directory as '.ratpoisonrc'. If not, you'll need to create it.
The manual includes some excellent information on what you can accomplish here and, depending on your package installation, you should find good examples of what's possible in the installation directory. You can, for instance, create several virtual desktops for your applications, or try using what Ratpoison calls Hooks to add simple scripted behaviour to your keyboard shortcuts.
You can add shortcuts for running specific commands, and even dump and restore specific application layouts, which is useful if you want one configuration for web browsing and another for programming. But if it's customisation you're after, there's only so far Ratpoison will go. You'll need to look for an even more advanced option.
We're now ready to delve into a window manager that's going to require a little more configuration to be useful, and one of the most configurable is the modestly named Awesome.
It describes itself as the next-generation framework window manager, and openly admits it targets itself at "power users, developers and any people dealing with everyday computing tasks and who want to have fine-grained control of their graphical environment".
Awesome is the epitome of what tiling window managers are all about.
It's not difficult to install. Your chosen distribution should already have packages, and you just need to let it install these, log out of your current desktop, and log in again choosing Awesome as your new window manager.
At this point, there's a chance you might see nothing at all. This depends upon whether your distribution has decided to bundle a default and sensible configuration file with its packages, or whether it expects you to set up a productive environment from scratch.
If not, you'll need to hunt for the file called '/etc/xdg/awesome/rc.lua', which is used by default on Debian-based systems, and it's this you'll need to edit if you don't like the default configuration.
Windows sans frontières
The best way to describe the desktop you see using this specific configuration is austere. It looks more like the last generation of computer desktops than something designed for the next generation, but you'll find that applications launch blindingly quickly, and that Awesome's best feature – its window tiling – is already in full swing.
Just open the menu from the small, inconspicuous icon in the top-left corner of the screen. You'll find that this hides the standard list of applications installed on your system, as well as more direct links to a terminal client and an Awesome menu for quick access to documentation and the configuration file.
When you first launch an application, you should notice that it won't have the window border because Awesome doesn't want you to go dragging windows about. Instead, it takes a very strict approach to where each window is positioned, and how new applications appear on the screen.
To do this properly, it has to stop you dragging them around yourself, which is why there's no window border. But this also adds a slight level of inconsistency, because certain applications, such as Google's Chrome browser, have their own borders, and you will be able to drag these around.
Speed == Efficiency
The best thing about Awesome is that it's quick, and this means you can switch between various tile configurations instantly.
There's even an on-screen button to make this easier, and you can find it in the top-right corner of the display. Clicking on this will cycle through the various layout modes on offer, and the icons are designed to illustrate what each mode does to your windows.
The first is a blank icon with a small blob on the bottom left, and this is the closest Awesome gets to being a floating window manager.
It means there's no layout, and you can move application windows as you need to. The next mode splits the main display into various sub-sections – two on the left half and six on the right – themselves split into two columns.
It's a layout that's perfect for a system administrator who needs plenty of terminals open showing log files, and perhaps a couple of sessions for doing some real work.
Many of the following modes are a variation on this layout, rotating the splits around each edge of the screen. But there are a couple that differ significantly, including the same spiral layout KDE offers, a single-application full-screen mode and a mode that seems to add windows randomly.
The best way to find one that works for you is to experiment with each one and see how you get on.
These tricks can also be accomplished by using key combinations. As we've alluded to before, getting the most out of a tiling window manager is all about learning the shortcuts that make things happen quickly.
Switching between tiling schemes can be accomplished by pressing the left Windows key on your keyboard and the Space key, and there are dozens of other combinations that can make using Awesome a much more pleasant experience than hunting through the launch menu might suggest.
You can resize individual windows by holding the Windows key and either H or Shift+H, and you can run applications from the command line with Windows+R.
You might also have also noticed that Awesome seems to have a considerable number of virtual desktops, as indicated by the horizontal list of numbers next to the launch menu. Clicking on these will switch desktops in the usual way, or you can use the Windows key plus a number to do the same thing from the keyboard.
But the interesting thing about Awesome is that these aren't called virtual desktops at all. They're called Tags, and they're one of its key features. The main idea is that you can send applications to a specific tag, for which you've created the most useful layout and configuration for that kind of application.
But to get this to work, you need to delve into the configuration file.
Configure or die
You'll quickly find that all paths within Awesome lead to the configuration file. Over time and use, it's likely you'll either get frustrated with the way a feature works, or with the unnecessary tiling modes, or will want to change keyboard shortcuts or add new ones. All of these things, and more, can be changed by editing a text file, and it's this that makes Awesome so useful.
The power within the configuration file comes from its use of the Lua scripting language. Every property within the file is defined using Lua and, as a result, you can create dynamic and adaptable solutions that wouldn't be possible with any desktop using a static configuration file.
To illustrate the lengths to which this can be taken, there's even an example configuration file that embeds a complete Space Invaders clone. However, before you attempt anything on quite that level, it's worth getting to grips with the basics.
To get started, move the global configuration file for Awesome into a '.config/awesome' directory within your home folder. Debian users will find the original file at '/etc/xdg/awesome/rc.lua', and moving this to a user's own configuration folder will ensure any changes you make to your own configuration won't be applied to anyone else's desktop.
You can then make changes with any text editor, although something with Lua highlighting, such as Gedit or Kate, works best. The configuration file is well documented, though you can make many small changes without resorting to the manual.
At the beginning of the file, for example, you'll find a section that lists the various layouts we scrolled through earlier, and you can easily remove any of them from your desktop by either deleting the offending line, or by commenting it out with a double minus symbol at the beginning of the line (--).
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Tutorial: How to perform a forensic PC investigation
When you have a technical interest in Windows or PCs in general, there are few things as fascinating as a good computer forensics package. This is partly because they're an excellent way to check exactly how someone is using a computer – the files they're accessing, the websites they're viewing and any information they may be trying to hide. It's a little sneaky, but if you have suspicions that, for example, an employee is doing something they shouldn't on a work PC, then this could prove very useful.
However, forensics programs also offer many other applications. They can help you recover deleted files, uncover even the stealthiest of malware, troubleshoot all kinds of PC problems, learn more about how Windows and your applications work, and let you pretend you're in your hometown's own version of CSI – perhaps.
This normally comes at a huge cost, with the top forensics packages running to thousands of pounds, but now there's a rare exception. PassMark Software has released a beta of a new package, OSForensics, which you can download for free and use until July 2011.
Despite being a beta, OSForensics is already fast, generally reliable, and packed with a host of useful features, so there's never been a better time to find out what forensics software can do for you.
Recent activity
Checking up on how other people are using your PC sounds a little morally dubious, but if you believe that they're engaged in activities you don't approve of – and maybe trying to hide them from you – then it seems to us that you're entitled to try to discover the truth. OSForensics can help you accomplish this in several ways.
Launch the program, taking care to give it administrator rights if you're running Windows Vista or 7 (right-click the shortcut and select 'Run as administrator'). Click the 'Recent activity' tab on the left-hand menu.
Accept all the default settings for the time being, click 'Scan' and, after a moment, OSForensics will list details relating to websites you've visited, files you've downloaded, documents you've opened, USB flash drives that have been attached to your PC, wireless networks that you've accessed (if appropriate) and more.
Some of this information is available from other sources. It's not difficult to browse through your web browser's history, for example, or check any cookies that have been downloaded, but other details are more unusual. If you're investigating a work PC, for instance, you could view the USB details to see if someone may be attaching unauthorised drives, perhaps in order to steal data.
Filter scan results
There's a definite advantage in having every detail available in a single interface though, and it's filterable, too. If you only want to look at the files that have been downloaded, for example, you can do this by selecting 'Downloads' from the 'Show Only' list.
If you're only interested in the events of the last week, select 'Search date range only', change the 'From' and 'To' dates accordingly, and then scan your system again.
If you click the 'Timeline' view, you'll see a classic timeline graph that enables you zoom in on a period of interest. You can click a year, a month or a day, then drill right down to the activities during that period. Right-click to export the results that interest you in CSV, HTML or TXT format.
The majority of forensic packages provide easy ways to search a hard drive beyond any system that might currently be installed (such as Windows Search), and OSForensics is no exception.
Click the 'Create index' tab, for instance, and you'll be able to choose a start folder that defines the file structure you'd like to search. Any subfolders will be included automatically, so to search the entire C: drive, you would simply specify 'C:\'.
It may take a very long time to index the whole drive, so if you only want to search for something in the Documents folder, browse to 'C:\Users\[Name]\My Documents' instead.
SEE HERE: Thumbnail previews are available in searches, making it easy to find anyimages you need, such as photos you've deleted and want to restore
The indexing is tool is already comprehensive, but you can make it even more so with a few extra tweaks. Click 'Config', then select both 'Scan files with no extensions' and 'Scan files with unknown extensions' to try to uncover content that other tools might miss. Then choose 'Files and unallocated sectors' to look for content in files that may have been deleted.
When you've finished, click 'Create index', then leave the program for a while. It will have to scan a huge number of files and the process will therefore take some time to complete.
It's worth the effort though, because when it's finished, you can use the 'Search index' tab to enter your key words and pull up matching files, images, emails and more almost immediately, including content that wouldn't necessarily be available if you used Windows search alone.
Deleted files search
If you're especially interested in deleted files, there's no need to spend lots of time performing unallocated sector searches. Just click the 'Deleted files search' tab and you'll find that OSForensics comes packaged with its own easy to use, built-in undelete tool.
The tool may appear confusing at first, but is straightforward if you understand how it works. On our test PC, for instance, the deleted files search announced that it would, by default, search the disk '\\. \PhysicalDrive0' – which, if you're used to Windows drive letters, isn't exactly clear.
It's not that bad, though. All '\\. \PhysicalDrive0' means is that the program will search all the partitions on your first physical drive, however many there may be. If you want to restrict your search to a particular partition, then select it from the list, which for us produced something like '\\. \PhysicalDrive0: Partition 0, C: [931.21GB NTFS'. Rather lengthy, but you'll know what it means.
When you're finished, click 'Search', and the program will produce a list of all the deleted files it's found almost instantly. If you know what you're looking for, enter all or a part of the file name in the 'Filter string' box, and click 'Apply filter' to display only matching files. (You can also filter by multiple file specifications if you separate them with semi-colons, such as '*.gif;*.xls'.)
BACK FROM THE DEAD: A simple Undelete tool enables you to view and recover deleted files
What the report won't give you, unfortunately, is any preview thumbnails, so if you're looking for images then you won't be able to spot them at a glance. However, if you suspect you've found the right file, then OSForensics can usually display it for you. Simply right-click it, select 'View with internal viewer', and the program will display the image. Not the right one? Use the 'Back' and 'Forward' buttons to step through the list.
When you've found what you need, right-click the file and use one of the 'Save' options to bring it back from the dead.
Signatures
One particularly interesting feature of OSForensics is its ability to create a signature of a particular set of files, folders, or an entire hard drive. You could create one signature now, for example, and another tomorrow, then use the program's 'Compare signature' option to show you everything that's been changed – that's new and modified files.
This clearly has all kinds of applications. You might use it to highlight changes another user has made to your PC. You could also compare signatures taken before and after installing an application to view the changes that it's made to your PC.
What about creating a signature of your Windows folder, then looking for changes that could indicate malware? Then you might create a signature of your entire system partition every day, then compare it to the previous version and look for unusual activity – whether it's malware or just applications that are creating unnecessary files.
Whatever your reasons, this is definitely worth trying and is very easy to do. Just click 'Create signature', then specify the starting folder for whatever you'd like to scan (try an entire drive to begin with), and click 'Start'. The process only takes a few seconds to complete, and you can save the results to your desktop.
Open a browser window and visit a site or two, then switch back to OSForensics and click 'Start' again to create a second signature of the same area. Finally, click 'Compare signature', point OSForensics to the two signature files and let it highlight the differences.
It's quick, easy to use, and can be very informative.
Our favourite OSForensics feature, for its sheer originality, is the Mismatch File Search. The core idea is a simple one. All you have to do is point the program at a starting folder – 'C:\' , say – then click 'Scan'.
The program will begin to scan your files, looking for any where the content doesn't match the extension. This might uncover all kinds of odd behaviour. If another user of your PC has renamed some videos to have ZIP extensions, for example, then the Mismatch File Search will reveal what's going on.
If a piece of malware has renamed key executables to an apparently harmless TXT extension, then again, this OSForensics report will highlight the change.
What's in a format
More generally, you'll discover the real file formats behind many of your applications. The program revealed that our old Empire Earth '.ee3sav' save game files were actually ZIP files, and that CyberLink's '.thl' files were PNG thumbnails – information that could come in very handy if these files were ever corrupted and we needed to make manual repairs.
In our experience, the file search can be an extremely revealing look at what's really going on with your PC. The same can be said of almost all of OSForensics' utilities – the program has many possible applications, and there's no telling what it might be able to do for you until you try it.
So give it a try – download a copy, explore the functions and see what this excellent forensics package can uncover about your computer, its software and users.
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Review: Dynavector DV-20X2L
We have yet to encounter a Dynavector cartridge that we don't like, but new ones don't come along very often, so when two arrive like buses on a cold night, it's a cause for celebration. As is the Japanese company's style, the new DV-20X2 is available in low and high output varieties, the low output version requires a transistor phono stage or step-up device, while the high can be used with valve and MM phono stages.
This, combined with a traditional two-gram down-force, makes the DV-20X2 a very easy cartridge to accommodate on modern turntables, or even older ones as long as they don't have a very low mass arm.
Flux control
As the name suggests, the 20X2 is the second incarnation of the 20X, a cartridge whose lineage goes right back to the eighties.
The 20X2 distinguishes itself with a new body – in fact, the body from the £1,000 XX2 MkII. It's made in machined aluminium and provides a rigid mounting for the otherwise nude generator and magnets. The flanks provide protection for the delicate innards and make alignment considerably easier.
This is the easiest Dynavector we've ever set up – hardly any kerfuffle at all.
The cartridge benefits from Dynavector's softened magnetism and flux-damping technologies. These are two methods by which the company's founder Dr Tominari, claims to minimise magnetic fluctuation. Something that while only minimal in MC cartridges is, in the doctor's opinion, detrimental to sound quality. It's possible to see the coil winding that is designed to damp stray magnetic flux on the front pole piece of the 20X2.
The 20X2's stylus is the same micro-ridge as found in Dynavector's 17D3 moving coil. It's bonded to a 6mm-long aluminium pipe cantilever. Signal is generated with the aid of neodymium magnets, the H model producing 2.8mV and the L a more modest 0.3mV.
Solid gone
The new bodywork makes the 20X2 look like a lot more cartridge than its predecessor, but this Dynavector is as solid as anything in the needle world. Value is really down to sound quality for the money, there are no features to consider, but if there were then ease of installation puts this in the top league.
Its competition comes from Goldring's Legacy (£595), the Ortofon Rondo Blue (£525) and the Grado Reference Master (£599), a wooden-bodied moving magnet.
The Goldring is probably the strongest, but we didn't find that it has quite the openness and power
of this Dynavector.
On the record
We set the 20X2L up in a Funk FX-R tonearm aboard the trusty Townshend Rock 7 and got the vinyl spinning, a process that continued way longer than the job required, but it was just too good to stop.
It took a little bit of fettling to get the best result – raising the downforce to the maximum recommended proved beneficial, for instance – but with that done there was an awful lot of musical detail flowing from the speakers.
It doesn't have the speed of its brother, the Karat 17D3, and the bass is a little on the relaxed side,
but the midrange and highs are extremely fine.
With a great phono stage, it achieves a degree of openness that's truly mesmerising. That's with the right record, of course, but that's almost any record that ain't heavily compressed and contains great music as far as we can tell.
The way that the various instruments and voices in a mix are presented in relation to one another is particularly good, as is the ability to cope with denser passages without the soundstage closing up.
Match point
Just to make sure all the bases were covered, we tried the 20X2L in an SME 20 with Series V arm.
This resulted in a similarly inspiring result and one where the bass was distinctly tighter. Which suggests
that this more conventional turntable is a better tonal match.
We also found that the DV likes a high-input impedance, 47kohm is usually best for MMs, but this MC sounded its best with the phono stage thus set.
This is a powerful, precise, revealing and open cartridge that warrants hi-res ancillaries, but will work a treat in any respectable turntable. In other words, the search for a Dynavector that we don't like will have to go on!
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Explained: How it works: the complete guide to HD
Next time you slip a DVD into your player and relax in front of your new 1080p HDTV to watch a crystal clear movie, take a moment to consider the digital video manipulation that's going on. After all, your DVD is encoded in one resolution and your HDTV is another, and not an exact multiple at that. How does it display a clear video with minimal image artifacts?
Television in the old days seemed pretty simple: it was analogue, it existed in the air around us and it used cathode ray tubes (CRTs). That was about it really, from the viewer's point of view.
Behind it all though, there was some pretty clever stuff going on – for the time. First, the framerate was geared to the frequency of the AC power that fed the television.
In England and the rest of Europe, which uses the PAL encoding system, the AC frequency was 50Hz, and so the framerate was set at 25Hz – enough to fool the eye into interpreting a rapid succession of frames as continuous motion. (The SECAM system is similar to PAL, at least as far as this article is concerned.)
In the US, which uses the NTSC system (people joked that NTSC stood for 'never twice the same colour'), the AC frequency is 60Hz and so the framerate was set to 30Hz (29.97Hz to be precise).
That's oversimplifying the situation a little. A television CRT displays the signal as a series of lines from left to right – a process known as scanning – jumping back to the left before scanning the next line. Scanning proceeds not by processing the lines in order, but by skipping lines.
The CRT scans all the even lines, jumps back to the top left, and then scans the odd lines, as shown in below. This is known as interlacing.
The display of all the even lines (or all the odd lines) is known as a field, with two fields per frame. This means that the field display rate is equal to the AC frequency (50Hz in Europe and 60Hz in the US).
For the PAL system, there are 625 lines per frame (only 576 lines are visible, the rest carry other information), and for NTSC there are 525 (of which 486 are visible).
Interlaced video reduces the bandwidth of the television signal by half, and helps smooth out motion (at least on an interlaced TV).
The odd field is displayed in 1/25 of a second, and remains on the screen (the phosphors on the screen maintain the image for another 1/25 of a second as they decay) as the even field is displayed. This remains on the screen for the 1/25 of a second that it takes for the next odd field to be displayed, and so on.
The fields are taken 1/50 of a second apart. In other words, a single frame isn't broken apart into odd and even frames; the frames are shot separately.
Converting framerates
Since film is shot at 24 frames per second, it must be converted to another framerate for viewing on TV – a process called telecine.
For Europe, the solution was to speed up the film by 4 per cent and convert the frames of the film into fields (usually by duplicating frames). The audio had to be corrected to ensure it wasn't too high pitched. This meant films ran quicker on television (a 90-minute film is 129,600 frames, which would take 86.24 minutes to show on TV), but this wasn't noticeable.
For the US, the problem was more acute: the framerate had to be increased from 24 to 30 frames per second. One simple way would be to duplicate one frame in four. However, this would produce jerky motion and was therefore never used.
In fact, the US telecine process (known as 3:2 pulldown) works by adding extra duplicate fields. In essence, four frames (or eight fields) were converted to five frames (10 fields) by duplicating two of the fields. This ensured much smoother motion in the video. The image below shows the process.
Each of the fields for each frame is shown in different tints of the same colour, with the earlier field as the lighter hue. As you can see, frame three of the video is formed from the earlier field of film frame two, coupled with the later field of film frame three; frame four is formed from the earlier field of the film frame three, coupled with the later field of film frame four.
The computer age
This was all good until computer monitors came along with the ability to display video, especially from DVDs. The biggest issue with computer monitors is that they don't use an interlaced scan system – they use progressive scan.
The display is still made up of lines, but the monitor scans them in strict sequence to build up a complete frame, not as an odd field followed by an even field. A PC monitor is also pixel-based – the signal displayed is digital.
The main issue then with displaying video on a computer monitor is that the signal, which is interlaced, needs to be converted to a progressive scan. This is called deinterlacing.
Each frame must be recreated from two frames, one odd and one even. Since each of the frames in a pair is taken at two slightly different times (1/50th second apart), if they were simply combined in a single frame, the motion of objects being photographed would be discernible as visible defects.
These defects are commonly known as combing, because the scans from odd and even fields wouldn't match up and would be visible as short lines. The image below shows the effect with a box moving from right to left.
The top part shows the interlaced version playing on an interlaced scan device; the bottom part shows that simple deinterlacing and playing on a progressive scan device produces a comb-like pattern.
Deinterlacing methods
Deinterlacing isn't just a simple algorithm. Much research has been done to improve the quality of deinterlacing algorithms, but the processing remains time consuming and complex, requiring the display to buffer fields, process them into frames and display them.
There are three key deinterlacing systems: field combination deinterlacing, field extension deinterlacing and motion compensation.
The first combines two succeeding frames to form a frame. Since the simple algorithm of weaving the odd and even scan lines in order produces combing effects, there are other techniques, such as blending (averaging out succeeding lines) and selective blending (averaging out succeeding lines for motion only, otherwise weaving them for frames that don't change). The problem with these techniques is that the resulting video tends to look soft or blurred.
The second system, field extension, either views the fields as actual frames (at half-height, essentially) so other techniques such as edge detection or sharpening can come into play, or doubles each line in each field. The problem with the latter method is that stationary objects in the video tend to bob up and down, and the height resolution is halved. This is known as the line-doubling technique.
The final system blends output from all the others to produce the best picture quality possible. The algorithms here try to predict the direction and speed of motion of objects in the video, minimising combing and softening.
All modern TVs (LCDs and plasmas) are progressive scan systems, but there are still problems once we factor HDTVs into the picture. Consider the standard DVD – it contains a video in what's known as 480p format. This is 480 pixels high (and usually 640 pixels wide for the 4:3 aspect ratio), and uses progressive scanning (the 'p' stands for 'progressive').
Some DVDs are 480i, where 'i' stands for 'interlaced'. A normal DVD player can read either type of DVD, decode and decompress, and produce output using interlaced scan for CRT televisions or progressive scan for LCD or plasma boxes.
If we connect the output from such a DVD player to a TV via the analogue inputs (composite or S-Video), we'll will get an analogue, interlaced display of the video on the DVD. It won't be completely sharp – it's not digital, after all.
It's better to pipe the video from your DVD into an HDTV digitally using the DVI or HDMI connection – avoid converting to analogue at all costs. The problem here is the difference in resolution. Suppose your HDTV is 720p. That means it has at least 1,280 x 720 pixel resolution for a widescreen display, and uses progressive scan.
Considering only the vertical pixel height, we have to convert 480 pixels into 720, unless we want to view the DVD output directly in a tiny window in the middle of the HDTV. We have to stretch the video approximately 1.5 times in size.
Video upscaling
Enter the video upscaler. This device sits somewhere on the path from the DVD player to the HDTV. It can be integrated into either device or can be a separate box altogether, although it's usually part of the DVD player (on the premise that upscaling should be done as close to the source as possible).
What the video upscaler does is analyse the pixel values and interpolate the values of extra pixels between them in order to stretch the 480 lines into 720. This is sometimes known as resampling.
The simplest scaling algorithm is bilinear interpolation. This is a simple extension of linear interpolation that you probably learned at school. With linear interpolation, you're trying to find the value of a function at some point given two known values at either side.
Essentially, you 'draw' a line between the two values at the end and interpolate along that line the value at the point in question. In the example below, we know the populations of England and Wales in 1811 and 1861, and estimate the population in 1851 using linear interpolation.
Bilinear interpolation moves that algorithm into two dimensions: you know the values of the function (in our case, colour values) at the corners of a square and you want to find the value at some point within the square.
Look at the bottom of the above graphs, where you're trying to find the value at x given the values at a, b, c and d. You perform a linear interpolation across the top (corners a and c, interpolated as ac) and bottom (corners b and d, interpolated as bd) of the square, and linearly interpolate between those two new points (from ac to bd, interpolated as x).
Bilinear interpolation is simple to code up, but when applied to images as we stretch them to fit a larger resolution, it causes aliasing artifacts and visual defects.
The process of bilinear interpolation relies on four pixel values to calculate another pixel value. This assumes that the values don't vary wildly across the image (we assume the colour function is fairly continuous with no major breaks), but as we know, images and video frames aren't like that. There are object edges where colour changes dramatically – 'breaks' in the smoothness of colour information.
In these cases, we should use more data points in our interpolation. This has the benefit of coping with edges in the original image, and providing a 'smoother' interpolation.
This is normally equivalent to using a quadratic interpolation. For a video upscaler, one of the most popular non-adaptive algorithms is bicubic interpolation, which relies on not the four closest pixels, but the 16 closest. Those pixels closest to the required point have a higher weighting than those further away, but all 16 are involved in the calculation.
The algorithm is known as non-adaptive because the whole frame is treated equally; no effort is made to identify fast-changing parts of the scene and other video effects.
Non-adaptive algorithms
Bicubic interpolation has the benefit of a fast calculation (slower than bilinear, but fast enough for video), but isn't the only non-adaptive algorithm. Others include nearest neighbour, spline, sinc and Lanczos.
To achieve better visual results, there are many patent-protected scaling or sampling algorithms that detect edges and apply algorithms to them to minimise the visual interpolation defects in those areas.
Others try to detect motion of objects in the video over several frames and apply algorithms to make motion smoother. With video, these algorithms have to be written to spot scene changes and not assume that they are fast motion.
These algorithms have to be fine-tuned for performance; they do, after all, scale video at 25 or 30fps.
The upscaler can't create detail out of nothing, but it does a good job of converting video without artifacts.
For better video, there's nothing for it but to use Blu-ray discs in a Blu-ray player. These are designed to provide 1080p video at 24 frames per second, and will play on a 1080p HDTV without upscaling.
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