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explain plz

Discussion in 'LCD & LED LCD TVs' started by 5tAr, Dec 28, 2004.

  1. 5tAr

    5tAr
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    Hi everyone

    Im new to this so bear with me plz :)

    can any of you guys explain the jiggerypokery about lcd screens and specs, eg do i need progressive scan, i have reviewed a lot of lcd tvs and some of the most expensive one dont have this.

    can somone explain contrast ratio?

    plus anything else i which is essential for a really good picture quality.

    thanxs

    ps sorry if i sound a little dumb :blush: but i find it easy to find out what specs each tv has but hard to find out what all the jargon means.
     
  2. ianh64

    ianh64
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    Hi and welcome to the forum.

    As far as LCD screens go, IMO, they have matured greatly over the last 9 months. So if you are looking for an LCD and great PQ, you need to get a rough idea on when it was introduced. Some bargain sets around at the moment are previous generations, and whilst whey may have been £6k when introduced, they would not look as good as a £3k display from the last 9 months. And those £3k displays from the last 9 months can now be had for 2/3rd of that price. As far as 32" and above displays are concerned, if its got a resolution of 1366x768, its pretty much guaranteed to be latest gen - at time of writing. One big exception is the 45" Sharp with screen 1920x1080. It is of even later spec and indicates the future direction of LCD panels, but at a price!

    Why do you want latest generation?

    Well, there are a number of things:

    Aspect Ratios:
    You really want 16:9 aspect ratio (which is 1.77 ~ 16/9 ~ 1366x768 ~ 1280x720 ~ 1920x1080 etc). 16:9 is useful as it is a standard for most widescreen broadcasts. Some DVD's are 2.35:1 or other, in which case you will still be letter boxed, by 16:9 is the best general purpose formats. Also of previous generations, whilst widescreen, are often 15:9 or 1280x768. If this is the case, you will either get borders, a squeezed picture, or both. If a DVD is 2.35:1 aspect ratio, if it takes your fancy, some dislays may have the ability to zoom the picture so it will be cropped or stretched.

    Contrast Ratios:
    Manufacturers often quote a contrast ratio. Whilst 800:1 is obviously better than 500:1, the actual value is meaningless in real life. The contrast ratio is the ratio between the measured brightness and dardness of the screen. One thing that LCD's are not so good at are black levels. Since they are backlit, you always get colour seeping through. So you could have alot of light seeping through but an extremely white white, and still have a very good contrast ratio. So it basically tells you nothing useful. The later panels are much better at pourtraying black and you can fine tune it with backlight settings and brightness. Unfortunately, short of seeing a correctly calibrated screen its something very difficult to judge. But, IMO, unless you are watching in a dark environment and want to compare a LCD with a CRT side by side, don't worry too much about numbers. You need to see if you are happy with the picture yourself. LCD's also have an advantage in rooms with ambient light at the matt finish of the display is good at reducing reflections so infact the LCD may not have such a good black leven as say a plasma, but as reflections are greatly reduced, the overall result is often better with LCD's.

    Response times:
    The latest generation screens have response times of 16ms and less. At this sort of rate, you are not going to notice issues except under very extreme conditions. I have a test disc that is worse case scenario and I see motion artifacts with a 14ms screen. I also see the same probelm with high speed scrolling horizontal titles, such as the closing titles of Balamory. Under normal viewing, I do not see any other instances of motion blur whether watching normal TV, fast action films, fast sport (F1 motor racing, football etc) or playing PS2 games. Motion blur was a problem, but with modern LCD's, it is pretty much a thing of the past.

    Progressive Scan:
    All LCD panels are progressive scan. So at some point, a standard definition video signal needs to be converted into a progressive signal. Whether this is best done in the source (DVD player etc) or in the screen all depends on whether the source or the screen is better at it. Progressive scan inputs are available via component or digital (DVI/HDMI) connections only.

    Scaling:
    A normal PAL TV signal is 720 pixels x 576 lines, interlaced. Assuming your LCD screen is 1366x768 pixels resolution, somehow it going to have to be scaled. This would normally be built into the display. However, like deinterlacing, this can often be done better at source using an upscaling DVD player or a standalone scaler. Again, scaled inputs are only acceptible via component or DVI/HDMI digital inputs. Some displays have marketing terms given to the scaling technology. Making a good looking scaled picture is not easy - information has to be generated from the source otherwise the image will look blocky. Some manufacturers give names to their technology that perform this, Philips call theirs PixelPlus, Sony call theirw Wega. However all displays need this technology so just because it does not have a fancy name, it doesn't mean that its not there.

    High definition:
    LCD's have the edge over other technologies for the future high definition services such as Sky, Blu-ray or HD-DVD. These future services and products will require the displays to beable to handle encrypted signals at certain resolutions and refresh rates. The encryption is called HDCP and is a digital only encryption that is optional on DVI inputs and mandatory on HDMI inputs. If your display does not have DVI+HDCP or HDMI inputs, you will not beable to make use of future high definition signals. Not all DVI inputs are HDCP compliant, infact most are not - these are for use as PC displays. Some screens are marketed as HD compatible but do not have these inputs. No matter what the guy in the Sony showroom says, or the guy in Curry's or Dixons, these screens are not HD compatible as the sticker was added before HD standards were published. The other thing about HD services is the resolutions and refresh rates required. As well as a DVI+HDCP/HDMI input, the display needs to accept 720p and 1080i input at 50Hz. Not all displays do or display without compromise. The majority of Sky transmissions will be in 720p and there is currently no information whether a 720p transmission can be output from the STB in 1080i or 1080i in 720p. Some sets are compromised with what they can display, for example the Philips 9986 cannot upscale a 720p (1280x720@50Hz) to the panel resolution of 1366x768 - the result is a bordered picture. Likewise, Sharp have admitted issues with some 1080i sources. My best advice is to see a demo of the source and display working together displaying non copy protected material.

    Native resolution:
    As has been mentioned, some latest generation displays have a display resolution of 1366x768 pixels. This is called the native resolution of the display. If you are using an external scaler, upscaling DVD player or using the panel with a PC, it is beneficial to get a 1:1 pixel mapping, often called dot for dot. You then run your scaler or PC at 1366x768 and the display does not have to scale the input further. Not all displays allow input at the native resolution, or allow the resolution but only at 60Hz. If this is important to you, then do a search of the forum for more information.


    I hope that this helps and does not make even more questions than it answers.

    -Ian
     
  3. 5tAr

    5tAr
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    wow thanks Ian

    you have really answered everything i needed to know :thumbsup:

    what a great forum, i will definatly post again if i am unsure of anything

    thanks again Ian for taking the time to answer :)
     

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