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HDTV Projector Advice from Just Projectors

Have you heard this one yet from a projector salesman…. "You don't want to buy THAT projector…it doesn't do TRUE HDTV." Well, certainly nobody would want to buy a projector that didn't do real HDTV, right? But they all claim to do HDTV. So what's the scoop?

It is easy to understand why the confusion exists. But it is also easy to sort it all out. First, let's start by defining HDTV. There are two common HDTV formats in use today, usually referred to as 1080i and 720p. The numbers refer to the number of horizontal lines in each frame of video (also known as "vertical resolution" since it is the number of horizontal lines as counted vertically from top to bottom of the screen). So in a 1080i signal, there are 1,080 lines per frame of video, and in a 720p signal there are 720 lines per frame.

 

The "i" and "p" indicate whether the signal is interlaced or progressive. In an interlaced signal, all of the even numbered lines are transmitted in one batch, followed by all of the odd numbered lines. (This is done to reduce transmission bandwidth.) In a progressive signal, all lines of the frame are transmitted at once in sequence. So with the interlaced 1080i signal, only 540 lines are recorded by the camera and transmitted at a time; they are then reassembled at the time of display. Meanwhile, with 720p, all 720 lines are recorded and transmitted in sequence.

Both of these signal formats maintain a 16:9 aspect ratio. That means the picture is 16 units in width for every 9 units in height. This is what has become known as the standard widescreen television format—all widescreen format TVs, plasmas, and projectors have a native 16:9 aspect ratio these days.

In order for an HDTV signal to maintain a 16:9 aspect ratio that matches the widescreen format, it needs to have 16 pixels on each line for every 9 lines of video in the frame. So a 1080i signal has 1920 pixels horizontally. That is why you will sometimes see the actual resolution of the 1080i format designated as 1920x1080. (If you divide 1920 by 16, then multiply the result by 9, you get 1080.)

Similarly, a 720p format signal has 1280 pixels on each line. So the physical resolution of the 720p format is often noted as 1280x720. (Once again, if you divide 1280 by 16, then multiply the result by 9, you get 720.)

So far, so good. Now….what is TRUE HDTV? This is where it gets confusing, because people use the term to mean different things. Some people think that the only real, legitimate HDTV format is 1080i because it has the highest physical resolution. So they refer to 1920x1080 as true HDTV. Others have been calling 1080i "full HDTV," presumably to distinguish it from the less full 1280x720.

Fans of the 720p format object to this. They point out that progressive scanning produces a cleaner, higher resolution signal when the subject is in fast motion. It has no deinterlacing fuzziness. And since the 1080i camera captures only 540 lines at a time, the actual resolution of 1080i when the subject is in motion is only 540 lines, not 1080. So many folks think 720p is better for rapid motion sports like football and soccer, while 1080i is better for, say, golf, where people are just basically standing around.

The fact is that both 1080i and 720p are great HDTV formats that look a lot better than standard television. Both formats are being broadcast by the major networks today, so your projector needs to be able to display both of them, and all projectors that are HDTV compatible do in fact display both of them.

So what does it mean to ask "does your projector display true HDTV?" Often what is really meant is, "does it need to re-scale the image?" In other words, does the video information coming in on the HDTV signal need to be either compressed or expanded to fit the physical resolution of the projector? In most cases, it does.

Any given projector has just one physical resolution, usually called the native resolution. Native resolution is the number of pixels actually available on the display. So an SVGA projector, for example, has display panels or chips with a native 800x600 pixel matrix. In order to display a 16:9 signal, it uses an active area of 800x450 on the display. So any HDTV signal that it gets, whether it is 1280x720 or 1920x1080, it must reformat (compress) that incoming signal into 800x450 before feeding it to its internal display. So no matter what, it cannot display any HDTV signal without compressing it, and losing a bit of image detail in the process.

This is true of standard XGA resolution projectors as well. They have a native resolution of 1024x768. In order to display a 16:9 image, they use an active portion of their display that is 1024x576, which is a 16:9 matrix. Therefore the HDTV signals, whether 1920x1080 or 1280x720, must be compressed to fit into a 1024x576 matrix before they are displayed.

Many new home theater projectors have native 1280x720 LCD panels or DLP chips. These are built expressly for the purpose of displaying HDTV 720p without needing to compress it or expand it. Some would say that projectors with the 1280x720 matrix are true HDTV projectors. However, some wouldn't, because when they get a 1080i signal these projectors still need to compress the 1920x1080 information into their native 1280x720 displays.

For the purist with unlimited funds, the only real, genuine HDTV projector is one with 1920x1080 internal resolution. These will display 1080i without any compression. There are a small handful of projectors on the market with this resolution, and at the moment they cost $20,000 and up. But these units need to reformat 720p signals, scaling them up to fit their native 1920x1080 displays. Technically, then, you could say that even these units are not true HDTV when it comes to 720p format.

The bottom line is that all projectors are built to scale a wide variety of incoming signal formats into their one native display. They will all do standard television, they will all do DVD, and almost all of them will do HDTV 1080i and 720p as well. In addition, most of them will display a variety of computer resolutions, including SVGA, XGA, and so forth. Really, when it comes to HDTV, there are only two circumstances where scaling is not required: 720p for a projector with 1280x720 native resolution, and 1080i for a projector with 1920x1080 resolution. Other than for those two unique matches, scaling is always required no matter what.

So this whole issue about "true HDTV" misses the point. Even the cheapest low resolution projectors will display HDTV pictures that look better than any television you ever saw. The fact that you are seeing a compressed signal is quite beside the point. Scalers have gotten so good these days that even low resolution projectors deliver amazing HDTV quality for the money, even after the compression. So who cares if it isn't "true HDTV?"

The real question is how much are you willing to spend on a projector? Generally, the projectors with higher native resolutions tend to cost more than those of lower resolution. With higher resolution you get reduced pixelation, and usually a smoother, cleaner, more filmlike image. And you usually get these improvements, to varying degrees, on all video sources whether they be television, DVD or HDTV. Getting better image quality across the board is usually a more important key to your overall viewing satisfaction than the question of whether the HDTV image is scaled or not.

Yes, it is true that today's 1280x720 format projectors are indeed particularly impressive for 720p display. But the amount of 720p material you will view compared to everything else will probably be rather small unless your weekly video entertainment consists mainly of HD sports broadcasts from ABC, ESPN, and Fox. And meanwhile, 1080i can look spectacular on a 1280x720 projector, even though the 1080i signal is compressed and not "true" 1080i.

Therefore, next time a salesman says, "Don't buy that projector, it doesn't do true HDTV," think twice and don't take his word for it. That relatively inexpensive projector you are considering just might deliver the best possible HDTV picture for the money on the market.

The Essential Projector Guide - Click to find out everything you ever needed to know about Projectors. How to choose the right projector, how the differences in technology effect you. Explanation of Projector terms and what that means to you.

Projectors are what Just Projectors have been specialising in for the last 10 years. To understand what the benefits are of a projector , it is useful to know exactly what a it can do and also the different type of technologies which will help you decide which one  maybe say more useful as a business projector rather  than say a home cinema projector set-up. Firstly  what is a projector;  it is in fact an electrical device that when light is integrated with an optics system then the end result is a large image being displayed from say a computer , video source or a games console.  Projectors can be manufactured in 3 main types, LCD, DLP and  Lcos  .

DLP Projectors- which stands for digital light processing is the newest entrance and it has  revolutionised not only the pricing but also the longevity of the projector. So what are DLP Projectors, well Texas Instruments back in 1987 developed the DLP chip.  As with all things in the projector world things have moved on, in March 2008 the new DPP1500 chipset was developed which has brought about the Pico or micro projectors which amazingly means that it can be the size of a mobile phone, although it is time to say that these micro pico projectors still need to improve their light output to really be taken seriously.

DLP Projector have the advantage of being cheaper to make, hence a cheap projector price is available, the projector lamps do not deteriorate over their lamp life and the actual projector lamps are themselves in the region of £115 rather than a price tag of £220. So DLP projectors work in a different way from LCD Projectors

DLP  work by thousands of mirrors set out in an array of pixels to replicate the projectors resolution. Each mirror is thinner than a firth of a human hair. With the use of hinges the dlp chip mirrors create light and dark pixels by being either off or on. The white light generated then is shone through a colour wheel of up to six colours. The human eye sees all the colours and the result is a full colour image.

Features about DLP Projectors are that they do not require you to maintain the projector regularly as they do not any filter. They are able to achieve high contrast ratios which means blacks are black which is a particular favourite for a home cinema projector user.  So after reading all this about DLP projectors you might wonder why we sell other types of projectors such as LCD or Lcos Projectors, the simple fact is that often the colours are not as accurate. Benq, Acer, Optoma and Viewsonic are the main manufacturers of DLP.

LCD Projectors have been in existence longer than any other technology. The colours on these are extremely accurate and if you need a projector for use as a photographer or graphic designer then we would always recommend a LCD Projector. How does an LCD or sometimes known as 3LCD projector actually work, well there are three liquid crystal panels , a lamp , prism and filters. In lamp shines white light through a polarizing filter, then a series of dichroic mirrors .The three colour red, green and blue are then sent to a separate LCD panel; remember there are three of them. From there the LCD panels send the light through the dichroic prism which recombines the light and sends it out the main lens in the LCD projector to the surface against which it is projected. Each LCD can control one colour. So if you were to see a picture of a red plane against a blue sky, the green LCD would block the light from passing to the dichroic prism and out the lens. This is very technical but the upshot is that accuracy of colours is the key reason why people choose LCD projectors.  The projector lamp prices are higher and there is often deterioration over a period of time but the quality of an LCD is superior to a DLP Projector and when buying a HD home cinema projector that is what Just Projectors would recommend. The main manufacturers for LCD are Epson, Sanyo. Hitachi and higher end Mitsubishi.

Lcos or Liquid crystal over silicon projectors are a hybrid of LCD and DLP .  LCOS will produce the most accurate video that is capable of far better than either LCD or DLP. How does Lcos projectors work, light passes through these LCD panels on the way to the lens and is modulated by the liquid crystals as it passes. Thus it is a "transmissive" technology. Lcos uses liquid crystals instead of individual mirrors. Three LCOS chips, one each to modulate light in the red, green, and blue channels which is like LCD panels  The end result is a very high resolution image, they tend only to start at SXGA (1365x1024). So if the technology is so good why aren’t all projectors made that way, the simple reason is price, which out of the reach of most people who are buying a business projector. The contrast ratio on a Lcos projector is often restricted to around 500:1, lamp life is often shorted with them not achieving much more than 1500 hours so cost of ownership tends to be very high. And finally they are not any ultra portable Lcos projectors .LCOS  technology is usually very high resolution, and typically higher in price than most LCD and DLP products. There is no such thing as an SVGA resolution LCOS projector, and we know of only one very rare XGA resolution machine. Generally LCOS machines begin to appear in the resolution class and higher. So by definition they are not cheap to produce as are not many are sold there are few volume efficiencies achievable. If you can afford Lcos then the well-informed people buying home projectors will recognise that Lcos projectors have a lot to offer as they have all the benefit of LCD but without as the pixels are significantly smaller there is no chicken wire effect. Also the pixels are much smoother then DLP sharp edges, which again helps provide the smooth image quality. Typical manufacturers of Lcos projectors are Canon and JVC

So now Just Projectors have explained how projectors work and the different types of technology it is important to work out which one is suitable for your needs. There are 5 main choices you have when buying a projector; what resolution, what brightness, what technology, what inputs can it take and what is the throw ratio. Looking at all of these in turn.

Brightness is measured in Ansi lumens, this is standard that every projector is measured against so that you know if its 3000 Lumens then its brighter than say a 1500 lumens. It is not true to say that a brighter projector is always better as especially for home cinema projectors you would really be looking for a high contrast and the more lumens then that will reduce the contrast available. So it’s important to get the right lumens for the right requirement. We typically recommend 1200-1800 lumens for home theatre and over 2000 lumens for the business projectors. Education projectors often tend to be lower lumens but in recent months it seems that 2000 Lumens now is the minimum requirement. If you have an audience size of more than 50 people which in turn means you need a larger projector screen then the lumens output should be in the regard of 3000 lumens. Large venue projectors or projectors for meeting rooms should be around 3500 lumens upwards. If you are a mobile projector user then lower lumens is often acceptable as you are trying often to have ultra light projectors which usually are no so bright. With the emergence of Ultra short throw projectors then the lumens output can be reduced as the image doesn’t have to travel so far to get to projector screen and the ambient light has less effect on the projector image. Typically ultra short throw projectors are around 2000 lumens.

Resolution is the number of pixels that the projector displays its native resolution. Often projectors will claim to be SXGA projectors but in fact that is not their native resolution and some compression is taking place. The lowest resolution that is acceptable is SVGA (800x 600). These are the cheapest projectors and really you should only buy these is you have a very low budget. Take a look on your computer and change the display to see what SVGA resolution looks like and you will see that it is quite poor. If however you only want to use a it for showing Dvd’s or video content then a SVGA projector would be suitable. We sell more XGA projectors (1024 x 768) than any other type; although surprisingly this isn’t the resolution most people pcs or laptops run at but as these are the most affordable and there are more of these than any others available.  WXGA projectors (1280 x 720) are increasingly becoming popular now that people are beginning to enjoy viewing presentation is wide screen format. WXGA projectors also have the benefit that they mimic a HD resolution 720p, so if you wanted to have a business projector but also take it home and maybe use it for gaming then it would be more suitable than an XGA projector. In the last few years people have wanted HD projectors to view TV, play games or look at blu-ray dvd’s. In the past these have only targeted the home cinema market but there is now an emergence for HD projectors for graphic design and web design companies. The increased brightness of say the Optoma EH1020  with its 3000 lumens and 1080p projector HD resolution is a prime example of how the market is changing. Canon in the past have really had the corner on the SXGA+ (1400 x1050) projector market with their Canon XEED range but again with the HD range increasing this seems to be a less popular resolution. We do however still recommend SXGA+ projectors for camera club and photographers mainly because they use the Lcos technology which has been previously explained above.

Inputs on a projector are so important so do not ignore them when buying.. All machines will be supplied with composite video (yellow) connection which is the simplest but poorest quality signal. All are supplied with at least one VGA or also known as RGB connection which links to your laptop or pc. The better ones have two VGA inputs which always you display more than one input source at a time. Having a VGA output is useful when you want to display both your projector image and also to be able to view your monitor at the same time.  Component video or BNC which is the red/green/blue connection is a much higher quality than the composite video as it provides a correct display of the signal

S-Video is a standard connection supplied and like composite it is used for video it does slightly differ as it splits the video signal into two different components: Luminance and Chrominance which results in a better image quality than composite video. HDMI is fast becoming the must have connection as it is the basically a digital version of a scart connection and it has the advantage that it also carries audio.

Having a RS232 is basically a control connection to allow your projector to communicate with other devices such as electric screen.

Projector Throw Ratio Probably one of the most important specifications of any projector but most people don't know about it or don't know how to calculate this very simple formulae. If you are in mobile situation you might have limited space so knowing the throw is important. If you are installing then it is vital. If you know you screen size width say in metres (SS) then multiply the throw ratio (TR) and that will say how far away - distance (D) you need to place the projector. If there are two TR's then that is the zoom within that range SS x TR = D Eg screen size 2m , Throw Ratio 1.9 - 2.1 = 3.98m-4.2m Calculation 2 (SS) x 1.9 (TR) =3.98m away - distance the projectors needs to be from the screen 2 (SS) x 2.1 (TR) =4.2m away - distance the projectors needs to be from the screen Another example- a projector with a fixed lens- so must be placed at a exact distance SS x TR = D Eg screen size 2m , Throw Ratio 0.5 = 1m Calculation 2 (SS) x 0.5 (TR) 1m - distance the projectors needs to be from the screen So as you can see the lower the throw ratio (TR) the close or short the throw the projector is. Handy Hint 1: - If you have a tricky installation situation choose a projector that has a larger Throw Ratio range eg 1.4-2.1 which will give you greater flexibility Handy Hint 2: If you choose projector with an unusually large throw or short throw then bear in mind that any installation that you set up will mean that the next time you purchase a projector you will need to get a projector with the same throw ratio, and therefore maybe limit your choice in the future. If you want to know how big an image a certain projector will produce from a certain size then the calculation is still very simple Distance away from the screen (D) divided by Throw Ratio = Screen width (SS) Eg distance away 4m , Throw Ratio 1.5 - 1.8 = 2.22-2.6m image width or screen size Calculation 4 (D) / 1.8 (TR) =2.66m width of screen required 4 (D) / 1.5 (TR) =2.22m width of screen required So at 4m the image size will be between 2.22m and 2.6m An example- a projector with a fixed lens- so must be placed at a exact distance D/TR = SS E.g. distance away 4m , Throw Ratio 2 Calculation 4 (D) / 2 (TR) =2m width of screen required This means if you need a larger or smaller image then you have to move the projector as there isn't any zoom on the lens Every one of projecotr pages has a projector throw distance /screen size calculator too to make it easier for you

The last thing to mention is what is the future of projectors , certainly getting smaller for the mobile presenter, led technology has seen the emergence of the pico projectors or micro projectors which weigh less than 50g’s and Just Projectors believes that the low lumens output will be resolved within the next 5 years. Led projector with a combination of DLP technology has also seen the first lamp free projectors being made available, notably the Casio XJ-S range. They have a lamp life of 20,000 hours and without the mercury in any lamp is now the green option. 3D Projectors have always been available but now they are affordable. Using active technology DLP projectors can now show 3D using a single projector using the active shutter glasses and the prices are under £500 for a 3D solution. However a note of caution as yet 3D projectors only works with Sky TV if you purchase an Optoma 3d-xl adaptor.

Hopefully you would have found this article about projectors to be useful but please contact us at Just Projectors for all your projector needs.


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