Matrix displays bite arse

Sure, CRT displays are bulky, consume piles of power and are heavy. But they can change resolution without a loss of … resolution.

See, High Definition TV runs at 1920 x 1080 – which, incidentally, a vanishingly small number of TV sets run at (ignore advertising about sets being HD-ready – all it means is the TV will understand a HD signal and happily convert it down to it’s native resolution). But converting a raster image from it’s native resolution down involves a loss of information; worse yet, if that resolution isn’t an integer multiple of source resolution, the downconversion algorithm has to make some judgement calls about which new pixel to push the old pixel’s information – so you can have some odd looking images, like horizonal or diagonal lines going… funny. Colour transitions can become forced too with a visible loss of colour depth. Converting up can also be a little strange, with some pixels odd colours (making the image look blurry) or straight lines becoming jagged. Given that signals might also appear in 704 × 480 (Standard Defintion) or 1280 × 720 (a high quality high definition signal not broadcast in Oztralia), aspect ratios on the pixels involved mean you need a native resolution not likely to be obtained for many years to get clean conversion between the resolutions.

CRTs don’t give a rat’s arse about conversion algorithms, and happily change the number of lines they throw on the screen in response to the number they’re given. The only difficulty you might encounter is the shadow mask or aperture grille.

LCD and Plasma display screens – generally TV monitors, and LCD projectors (and for that matter, any other matrix-based projection technology) have a failure mode that analogue CRT displays don’t exhibit:

Dead pixels.

Stuck on or stuck off, dead pixels are a one way street. You don’t see that kind of failure in CRTs. And I’m not aware of any TV manufacturers who guarantee their product against this particularly annoying failure. No-one is told about it at purchase time, but I’m predicting in three to five years time there’s going to be an uproar about it.

Anyone bought a new matrix TV lately? Happy about it?

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1 thought on “Matrix displays bite arse

  1. Martin

    My (perhaps limited I admit) understanding is that there are good filtering algorithms to upscale and downscale the resolution of raster images. In fact you could hardly call them algorithms, they are relatively simple formulea (harder to derive but simple once derived). I am sure I have seen them in action and they looked quite good. I think I have even seen them on HD TV’s showing standard resolutions. And I think that on a hi res CRT screen, upscaling a normal image looks better than dispalying it at its natural resolution. Well OK, I wouldn’t go so far as to say that it worth spending big bucks on a 720 line HD TV if we are only ever going to get 1080 transmisions, but I don’t think it will look worse than a standard res TV.
    These algorithms don’t work that well on computer monitors because the images on these have sharp edges. But movies are a completely different issue.
    These algorithms are very well known amongst engineers and are light weight enough to cheaply implement in real time. So I would expect manaufacturers do use these on high end TV’s, at least the big name manufacturers. They should work well for non integer multiples/fractions.
    I cannot really recall for sure if I really have have seen these things in action and working well, but until I read this I was sure I had and thought this simply was not an issue. In fact I do wonder if you have really seen these problems on TV’s not just computer monitors.

    And yes I do have a standard res LCD TV and am really very happy with it. This doesn’t say much as it replaced a 41cm Teac from KMart. We bought it mostly for its asthetics as we don’t like 51+cm globs of plastic in our lounge room. (OK some look more like desgner blocks of plastic than globs). Had it for about a year and it certainly is better than the TV it replaced in most repsects. We had quite a few concerns about it (the image scaling was not one of them, or really the dead pixels either) but we have been satisfied in every respect including image quility, sound, reception, colour range and even viewing angle. We paid well above CRT prices lot for it a year ago and would like to think it will keep working well for at least 5 years which is something we will have to wait and see. (Well really I would like 10 years but that is unreaslistic). Since it is standard res and we are using it with analog signals there are no issues about scaling. For widescreen signals, even some videos are wide screen – yes the tape type things, it seems to display in widescreen with a black bar on the top and bottom, more so than CRT TV’s. This really doesn’t seem to bother us. (And it may acually mean the TV is doing some vertical scaling.) It does mean we might have been able to get a better overall image size, for the ever incresing number of wide screen transmissions, with a wide screen TV of lesser vertical dimensions.

    But overall I agree that the Hi Def standards are a mess (even if that isn’t really the gist of your article). I don’t know what digital transmissions are or will be, even if they are Hi Res. I know what 1080i and 1080p mean but I suspect most peaople don’t and I certainly don’t know what campatability issue this raises. If 1080 (i or p) is going to become the standard then this is a problem as 1080 TV’s are still uncommon and haven’t enjoyed the price drops of 720 and standard res TV’s. Compatbility with HD dvd’s is still completely up in the air. And whilst I think 720 line TV’s will nearly always look better than standard res TV’s (even for LCD/plasma), I dont think they are worth the extra cost.

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