Television Terms - TV Glossary
Ah, so that's what it means...
The world of televisions can be a confusing place, where lots of buzzwords and techno-speak can be daunting to the uninitiated.
We’re guilty of bandying some of them around, ourselves, in our in-depth hardware reviews but sometimes it’s just unavoidable to get the real meaning across. So, in this latest guide, we’re going to talk you through exactly what the most used words and phrases mean and, don’t worry, even when things get technical, we’ll try and make it as simple as possible to understand.
We’ve already shown you what to look out for when buying in store, how best to connect your equipment to your new TV and how to set up those sources once in situ. We’ve even talked you through 3D technology and whether you need a Freeview or Freesat capable TV but now it’s time for some jargon-busting to increase your awareness even further.
ScalingYour television will have a certain amount of pixels (tiny dots of light) that will form the overall picture at a certain resolution – the higher the resolution the more detailed and defined the picture will be. We’ve already covered what all the different resolutions mean in another piece but for most people, at this current time, we will be talking about either Full HD (1080p) or HD Ready (720P) televisions. Regardless of what resolution the source material is, your TV will then process the video signal to match the number of pixels it has. For example, if you’re playing a DVD your TV will take the signal which has a resolution of 720 x 576 and then process it to fully utilise all the available pixels. This process is called scaling and can be done both up and down, as some 720p (HD Ready) TVs are able to accept a Full HD (1080) signal. The quality of scaling in the latest televisions is generally very good but it’s always something we test for in our reviews.
Progressive & Interlaced signalsThis one is slightly more complicated but we’ll do our best to make it easy to understand. As a rule of thumb, most movies are shot in what is called a progressive format, whereas the majority of television is delivered interlaced. When we say progressive, what that means is that each frame of the material is presented one after the other with both odd and even lines shown together to make up the moving image. On the other hand, interlaced content is produced by blending elements from two adjacent frames, splicing odd and even lines together to form each frame (see image below) – one frame will have the first, third, fifth etc lines while the other will have the second, fourth, sixth etc and they are blended (deinterlaced) so quickly that the eye sees them as one solid image. In most cases, a high definition television should have no issues displaying progressive material but deinterlacing is more taxing on the processor and, again, it’s something we carefully test for in our reviews.
FramerateQuite simply this is the number frames displayed every second to produce the moving image. The majority of films are shot at 24 frames per second, progressively, whereas typical television content is captured at either 25 frames (progressive) or 50 frames (interlaced). In terms of Blu-ray discs, the vast majority will be what is known in shorthand as 1080p24, where 1080 is the number of horizontal lines of resolution, ‘p’ denotes the fact it is progressive and 24 is the number of frames per second. Most DVDs you have will be delivered to your TV at 576i50, where there are 576 lines of horizontal resolution shot at 50 frames per second in interlaced format. The same applies for standard definition broadcast TV signals but if you have an HD set-top-box, the signal being sent to your TV will either be 1080i50 or 1080p25 and hopefully you can now decipher what those both mean. Confusingly, in other regions of the World – notably the USA – broadcasters have elected to go with either 720p60 or 1080i60 as the standard.
Screen Refresh RatesIn simple terms, refresh rates refer to the number of times a television ‘scans’ the signal per second and is measured it Hertz (Hz). The reason different territories use different framerates is tied in to the electricity supplies used in the countries in question. In the UK our electricity is delivered at 50 Hertz (Hz), whereas in the USA, for example, their electricity runs at 60Hz. This is a historical thing and there’s no longer a need for the TV to be synchronised to the mains supply but we’re stuck with it for the time being. In actual fact, the vast majority of HD TVs can run just as happily in 50Hz as they do 60Hz and the majority will also refresh in multiples of 24 to match the frame rate used in movies, e.g. 48-, 72-, 96Hz etc. Having a higher number here is better as it means the image should exhibit no flicker and the perception of moving images will be smoother. You will now see televisions marketed as having extremely high refresh rates – anything up to 3000Hz – but this is slightly confusing terminology on the manufacturer’s behalf and actually refers to the number of times the backlight can be switched on and off, per second, rather than the number of times the screen is actually refreshing. Still, bigger is generally better but, once more, these are claims fully investigated during our reviews
Don't be misled by manufacturer claims of incredibly fast screen refresh rates
Motion ResolutionIn an ideal world, your TV would be able to display moving images at their full resolution with perfect clarity but limitations in the display technologies mean that is not the case. There are a few tests we can run to assess what an individual TV is capable of and a typical figure for an LCD/LED TV is around 400 lines of resolution, under movement, from a possible 1080. For most people this is fine and the eye and brain become accustomed to the inherent blur of images, when moving, but some are more bothered by it than others. For that reason most manufacturers include some optional motion processing, in their higher end models. This calculates what information should be contained in a given frame by analysing the ones either side. The processing then inserts a made-up (guessed) frame (or frames) to give the impression of greater clearness. Some systems are better than others, however, and based on our experience we would only ever advise using it at very moderate settings and rarely, if ever, would we engage it when watching movies, as the processing typically turns what was 24 frames per second content in to, effectively, 60 frames per second and thus spoils the look of the film.
Cadence DetectionIf you’ve managed to follow everything above, this will be a fairly simple concept to grasp. As an HD TV inherently displays images in a progressive manner, on top of the deinterlacing it sometimes has to perform, it sometimes has to deal with content that was captured progressively but sent in an interlaced signal. A good example would be your typical DVD player connected to your TV via a Scart lead. When watching a movie, in almost all cases the DVD player will be sending a 576i50 signal to the TV with material which was encoded at 576p25. A properly encoded DVD will contain metadata (think of them as flags) to instruct the TV that the adjacent 1/2, 3/4, 5/6, 7/8 frames actually contain the same information and therefore don’t require blending together (deinterlacing). If the TV fails to detect that fact then it will try and perform unnecessary deinterlacing which can result in unsightly picture artefacts.
Input LagInput Lag is defined as the time between when the user presses a button on a game controller and when the action happens on the screen. There are many factors that contribute to the amount of input lag, including whether you are using a wired or wireless controller, the network lag (if you are playing online) and the processing speed of the console itself.
However, the factor that we test for in our reviews is the input lag caused by the image processing of the TV. Image processing all takes time and increases the amount of input lag. Most TVs include a Game mode that is designed to bypass the majority of the image processing, thus keeping the input lag to a minimum. We use a special input lag tester that works by producing a standard 1080p HDMI signal and measurements are accurate to +/-0.1 milliseconds which offers far greater accuracy than other methods. Input lag is not to be confused panel response time, which is the time measured for a pixel to go from grey to white and then back to grey again.
You can see some of the most responsive TVs for gamers here.
Input lag is not to be confused with panel response time, which is the time measured for a pixel to go from grey to white and then back to grey again.
Industry StandardsThe industry standards tell us where the primary colours (red, green and blue) and the secondary colours (cyan, magenta, yellow) should be for playback. As these these are measurable and repeatable standards, i.e. a benchmark, this is the reason we always calibrate the review televisions.
For HD material the standard is called ITU-R BT.709 (or Rec.709) and for SD material we use the PAL standard, which is actually very close to Rec.709. Both of these colour standards have the same white point of D65 (see below). Film and TV productions use these standards for mastering and broadcast of content. A display must be able to conform to the standards to replay that material as intended.
By following industry standards we can objectively assess a display device to see if it is capable of playing back film and TV material as intended. AVForums is the only UK website where all our TV reviewers are ISF and THX trained and certified so we are capable of measuring displays against industry standards, using accepted techniques and equipment.
CIE ChartThis is a graphical representation of the accuracy of the colours measured in the TV. We use the chart in our reviews is to illustrate how close a display device is to industry standards. The triangular outline represents the full extent of the colour gamut (palette) we are measuring against and the small boxes at the points represent where we want the three primary colours (red/green/blue) to be at fully saturated levels. The boxes on the edge of the triangle, between each of the primary colours, represent the ideal points for the secondary colours – cyan, magenta and yellow.
Looking at the example in the pictures above and below, we can see the one at the top has colours measuring some way off their targets, while the one beneath is almost perfectly accurate, meaning it will make a far better job of displaying films and TV true to the industry standards.
Colour GamutThis is the range of different colours that a TV can accurately display; the more colours, the wider the colour gamut and the more saturated and intense the colours will be. Most modern displays have a wide colour gamut available out of the box, which when displayed on screen adds an artificial punch to the picture. If the gamut is over the accepted standards then picture quality will suffer with colour inaccuracies. Some people will misinterpret these bright, vivid and over saturated colours as being appealing, but when was the last time the football pitch in real life looked neon green?
Rec. 709The Industry Colour Standard ITU-R BT.709 (AKA Rec 709) is used in all production and mastering of HD TV and Movie content and it’s what me measure the TVs against, in terms of colour accuracy.
Rec.2020Rec. 2020 is not just a new colour standard for the new generation of Ultra HD TVs and content, it also defines factors such as resolutions and framerates. As we can see from the chart below, where the outside triangle represents the Rec. 2020 colour gamut and the one inside it the old Rec.709 colour points, Rec. 2020 has a far wider spectrum of colours available. We should point out that there are currently no TVs capable of hitting Rec.2020 colour fully and nor is their any content available. In the meantime, we anticipate that most Ultra HD content, including 4K Blu-ray disc, will be mastered in the Digital Cinema (DCI) colour space which is in between the two.
High Dynamic RangeIn simple terms, HDR is a way of displaying the wider dynamic range inherent in the original capture of content. A film camera or a modern digital camera is capable of capturing a higher level of brightness (luminance) and a wider array of colours than the Standard Dynamic Range (SDR) content we're used to seeing now. However, if a transfer can be created that retains all this luminance detail and a display is capable of showing it, then the resulting image will be a better representation of what the human eye is capable of resolving. It’s important to realise that HDR isn’t simply about increasing the brightness of an image, although that is a common misconception. The idea is to increase the overall dynamic range between black and white by making the dark parts darker and the bright parts brighter, whilst retaining detail when both are in the frame. So for example if the image was of the inside of a room you could see details in the dark shadows but also make out details through the brightly-lit window. However, it isn’t just about the difference between the darkest and brightest elements in an image, HDR also calls for greater expression and detail within colours too; so, HDR will use a wider colour space than the current standard of Rec.709 (see above).
D65D65 is a commonly used white reference approximating to daylight. The International Commission on Illumination (CIE) defined D65 as the numerical representation of average daylight. We can see in the CIE chart below that, in addition to the squares for the primary and secondary colours, there is another box towards the middle representing D65.
White BalanceWhite Balance, Greyscale, Colour Balance and Colour Temperature all refer to the correct colour of white within video signals. A display’s White Balance, Colour Balance or Temperature is referred to as the Greyscale. Most TVs will have user changeable presets for colour Temperature, Balance, or White Balance. These are normally called Standard, Cool, Warm and Natural. In most cases, the warm preset will be the closest to our desired D65 point. Video white is not a brilliant white colour.
GreyscaleThe greyscale is the colour of white from complete black (0% brightness or luminance) to full white (100% brightness or luminance). In a television, white is made up of Red, Green and Blue light mixed in the correct proportions. At every step from 0 to 100% the brightness or luminance is the only part that is reduced.
When looking at our graphs in the reviews you will see that the Greyscale is represented by Red, Green and Blue Horizontal lines. That graph shows 0% brightness at the left to 100% brightness on the right. This shows that Red, Green and Blue are mixed correctly to make the colour white in our greyscale and that we will not have any errors in the image where there is a colour cast or colour shift. For example, if there is too much green energy in the greyscale, pictures can exhibit an unnatural green tinge, i.e. a colour cast.
In the examples above and below the image on top has an inaccurate greyscale, with an excess of blue in the greyscale, where the one underneath has a virtually neutral mix of red, green and blue, meaning it will have no colour cast to the images.
The easiest way to get your head around the differences between colour points such as in a CIE chart for Rec.709 and the Greyscale is to think of video being delivered in two separate parts. Think of it as a black and white backbone which is the Greyscale and a coloured element is then added on top of that, this is our colour points or colour gamut.
In technical terms gamma represents a numerical parameter that describes the nonlinearity of luminance reproduction. It is a complex subject, not made any easier by the official term that is now EOTF (Electro Optical Transfer Function), and can be quite difficult to understand because it involves concepts from four different but related disciplines: physics, biology, photography and video. Well done if you've read this far...
The easiest way to think of gamma is as the brightness of white. We set a gamma target prior to calibration (usually between 2.2 and 2.4 for a darker room) and our software will then measure the TV against that. The higher the gamma number the darker the picture.
Delta Error/ deltaE/ dEThe DeltaE is a number that represents the extent of a particular error. A delta Error of 3 is considered as imperceptible to the eye and a DeltaE up to 5 is typically considered as acceptable. If we are measuring delta Errors above 5, you are likely to notice a colour cast, as explained above.
Dirty Screen Effect (DSE)Dirty Screen Effect (DSE) is a panel uniformity issue that looks exactly as it is described. It will be most easily visible on solid blocks of colour and it’s usually worse where the camera is panning across the scene. Typically it is characterised by a mottled effect on screen, with grey or grey/brown splodges visible – think of something like mud hitting a car windscreen. You can sometimes mask it slightly by reducing Backlight and/or Contrast settings.
Panel Banding/ Array BandingSimilar to DSE, discussed above, with LCD/LED TVs it is sometimes possible to see the internal structure of the panel behind the screen and, again, this is usually easiest to spot when the camera is panning. It will normally manifest as vertical lines (aka bands) on the screen with alternating levels of brightness, e.g. dark/light/dark etc. Again, you can slightly limit the effect by reducing the panel brightness using the Backlight control.
Colour Banding/PosterisationThis is an entirely different kind of banding effect where there are problems with showing colour tones correctly. Pictures are usually made up of colours blending gradually (gradations), from one to the next, but sometimes these transitions can be seen, resulting in banding being visible. This can be caused by both the video source not being top notch or it can be as a result of the TV not handling the images correctly. In the latter case, it is something we would associate more with plasma TVs but LCD/LED TVs with cheap panels can sometimes show it.
Clouding, Light Pooling, FlashlightingThree words to describe the same thing and they all refer to screen uniformity issues. On your LED/LCD TV you might be able to see patchy areas of the screen that are brighter than the rest. It’s easiest to see when the screen is black, or at least very dark, and it’s caused by uneven dispersion of the backlight. This is something we regularly see in review samples, to some extent or other and if it is particularly bad it can be very distracting.
Edge Bleed/ Corner BleedThese traits are very similar to the issues noted directly above, only as the names would suggest, they are uniformity issues specific to edges or corners of the screen. Again, most visible on black or very dark screens but you might be able to see it in other situations.
HDMI 1.4/2.0/2.0aFor regular High Definition (1080P) video, and for that matter 3D content, an HDMI 1.4 port on the back of your TV will be sufficient. If, however, you’re planning to take the leap in to 4K with an Ultra HD TV, you will want to check its ports are at least HDMI 2.0 compatible. The latest revisions of the HDMI spec are really all about 4K Ultra HD. Whilst HDMI 1.4 is capable of carrying a resolution of 3840 x 2160 pixels, it can only do so at low frame rates, so it is not future-proofed against advances in Ultra HD delivery technology. Where an HDMI 2.0a connection becomes important is when your TV is High Dynamic Range (HDR) capable and a 2.0a port is needed to process the HDR (meta)data.
HDCP 2.2The very latest version of High-bandwidth Digital Content Protection (HDCP) is 2.2 and you should get compatibility via any HDMI 2.0 labelled input; meaning when 4K Blu-ray players arrive, or if you want to use any other UHD video source, this will be your go-to connection. For connected devices with older HDCP compliance that are connected to HDMI 2.0 inputs, you might need to change a setting in the user menus concerning HDCP version, to ensure everything works as expected – check your owner’s manual for details.
Other Review Terminologies
Black LevelsBlack is black, right? Well, not quite in the world of TVs. Due to technological constraints most TVs emit some level of light even when the video signal is telling them to display black, resulting in what is actually a dark shade of grey. For the technically minded, that is referred to as the Minimum Luminance Level (MLL) but we usually just term it as the black level to avoid confusion. Some TVs can produce a much darker grey than others, meaning the ‘blacks’ look nice and deep and this produces pictures with greater contrast (see below). Whilst all the hardware team do have very accurate measurement tools, we always warn that our black level readings should be taken in context against other measurements we have taken, and not as a reference. We use the internationally recognised cd/m2 (candelas per square metre) unit of measurement for our luminance readings.
Contrast RatiosThis one is easy-peasy. The contrast ratio of a TV is simply calculated by measuring the brightness of white (peak luminance) and then dividing that by the black level (minimum luminance level) measurement. So, for example, is a TV produces 120 cd/m2 for white and 0.05 cd/m2 is its black level we get a contrast ratio of 2400:1. The higher the contrast level, the more striking the picture will be, so a higher number is better here.
On/Off Contrast Vs ANSI ContrastWe typically measure contrast ratios in two ways. The first method is called On/Off contrast and is calculated by measuring an all-white screen and an all-black screen and then the white measurement by the black one. The other method is to use what is called a chequerboard pattern (see below) where the screen is divided equally in alternating black and white blocks. We measure all the black and white blocks and then get an average for each and then divide the average white level by the average black. This is called the ANSI contrast and should be more representative of what a TV is capable of in real world performance terms. After all, it is rare that you will be watching anything that is completely black or white.
Dynamic RangeThis is akin to contrast but slightly different. Where contrast is just the difference between the darkest elements of the image and the brightest, dynamic range is easiest to think of as the expression of everything in between. A given colour has almost limitless shades (steps of brightness) that the eye can see but the content you see on your TV is limited by compression techniques. For many years we have been watching 8 Bit video, which provides 256 shades per colour, but the 4K revolution means we will soon be seeing content based on 10-bit video, which will provide 1,024 steps per colour. That should mean images that have far more realism as it’s closer to what we observe in real life, i.e. they have greater dynamic range.
Viewing AnglesThis is a very simple one to consider, really. Without going in to the technicalities, some TVs are better than others when viewed from off-centre. When moving to the sides, you may notice that colours and contrast are more washed out and, depending on your room lay-out, this might be an important factor when considering a new TV. If you’re in the market for a new LED/LCD TV, look out for those that advertise themselves as having an IPS panel if wide viewing angles are a necessity. Or, if you have plenty to spend, OLED TVs offer the best off-axis viewing experience.
Backlighting SystemsWhilst a Liquid Crystal Diode (LCD) pixel will illuminate, it can get nowhere near bright enough to produce an acceptable picture on your TV. For that reason, an LCD TV will need some form of backlight and these are almost all Light Emitting Diode (LED) based nowadays. In the early days of LCD TVs they would typically use Cold Cathode Fluorescent Lamp (CCFL) systems but LED’s are more energy efficient and allow for slimmer designs. The LEDs can be placed behind the panel, which is termed as direct or full array backlighting, or at the sides which we call edge-lit. In theory, a direct backlighting system should cause less screen uniformity issues but that’s not always the case and it’s something we always assess in our reviews.
Dimming SystemsBroadly speaking, dimming systems fall in to two different types and they are found in many LED/LCD televisions to improve the perceived contrast and black levels. A dimming system can be global or local, where global refers to an overall dimming of the picture and local means that smaller portions, aka zones, of the screen are dimmed. Clearly, a local dimming system should be more accurate than a global one and the more dimming zones the better. On top of that, a TV with direct LED backlighting (see above) should have better local dimming than one that is edge lit although, again, this is not always the case.
So there's a summary of some of the most common terminologies and nomenclature you will hear and read when researching your next TV. If we've missed any that you would like to see explained, please let us know in the comments section, accessed from the 'Discussion' tab below.
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