Newbie trying to understand scaling + dvi - please correct me if I am wrong

Discussion in 'Projectors, Screens & Video Processors' started by Nabs, Aug 3, 2006.

  1. Nabs

    Nabs
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    I have been reading about scaling and dvi etc and would like to ask those more knowledgable if I understand ok,

    From my understanding scaling can occur at 3 levels, in the source (e.g. dvd player), via an external box and/or in the screen (in my case this will probably be an lcd). I presume if scaling is done only once and with the best scaler (whereever that lies amongst the 3 levels) and kept in the digital domain in the rest then that would be better. Then the transfer in the digital domain will also lie on the quality of the digital interconnects.

    I presume if the display screen cannot take 1 to 1 pixel mapping from an external scaler and/or dvd scaler then that means that one with have 2 scaling operations anyway and hence theoretically will probably introduce more artefact.

    Now I think sdi means that the signal from the disc is taken unprocessed from the dvd in digital form and therefore bypasses the disc processor, this then can be either passed to a screen or an external processor (naturally the latter being a more expensive option). Therefore the best picture connecting dvd directly to screen would be:
    1. If the dvd player does not have a scaler - sdi output to screen. Even if the dvd player has an hdmi output I would presume there would be more processing anyway due to HDCP and therefore the sdi output would be superior.
    2. If the screen scaler is better than the dvd scaler - SDI dvd player feed direct to screen
    3. If dvd scaler is better than screen - dvd scaled and passed directly to the screen, unless the screen rescales the feed anyway (as it cannot perform 1:1 picture mapping)

    Of course if one has an external scaler then the 3rd tier would also apply but again benefit would probably depend upon the display accepting 1:1 pixel mapping from the scaler (at whatever resolution).

    So really what one needs is a list of which scalers/ scaling chips are better and where to find each!.


    Personally I am thinking of making a future purchase of the next generation Loewe spheros lcd, this is supposed to accept 1080p feeds but I am not sure if it does 1:1 pixel mapping yet. If one assumes it does then the best picture would then be simply dependant on scaling; given that I cannot afford an external scaler yet, then the best picture from dvd I probably will get, will be I presume an sdi-dvd player connected direct to display, or at a second an hdmi-dvd player connected to a display.

    As sound is equally important and as I have an Arcam AVR then if I think down the Arcam route then it probably would be an sdi Arcam 29 or would it be easier and equally good just to go via a straight Arcam 137 without sdi. Naturally this is currently theoretical and suggestions or corrections to my logic would be appreciated.
     
  2. Welwynnick

    Welwynnick
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    Nabs, I'd say you've pretty much got it, but I wouldn't presume to use SDI unless you decided to use a scaler that happened to have an SDI input. You won't find many screens with SDI inputs. Those are optional on Panasonics, but I've never heard of anybody using one.

    If you are going to use a scaler, then you really want a player and a display that will support digital video in the native format for that equipment. But that doesn't always happen; the interface is all too often 576p, 720p or 1080i, and that doesn't cover the native format of many sources or displays.

    However, if you just want to keep your options open for a scaler later, then you could have an after-market SDI modification done on a DVD player, but DO think carefully about the display interface. Most displays these days are 1366x768, but accept 720p over HDMI. May as well use 576p in that case, as it will eliminate one scaling stage.

    Nick
     
  3. Joe Fernand

    Joe Fernand
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    Hello Nabs

    Due to the lack of an encryption layer SDI is very firmly kept in the Pro Video market.

    As you have seen a few enterprising folk have come up with work arounds to enable you to modify certain Source devices to be able to output an SDI signal - though these are generally being used as a Transport to 'front end' an SDI equipped Video Processor.

    The Video Processor is then Outputting a Digital signal via HDMI or DVI as you wont find any Consumer Displays fitted with SDI (or with the option to mod them to accept SDI) and where you can fit SDI boards to 'Professional' Displays they often only work with a very narrow range of Input signal formats.

    The Arcam FMJ-DV29 is a great choice as its HDMI Output can be set to Output an Interlaced YPbPr signal which is as close to SDI as your going to get if you want to use it as a Transport for a Video Processor - and if you get the urge it can also be modified with an SDI Output board.

    Scaling is just one of the myriad of processes that go into producing a decent video image and whilst 1.1 pixel mapping is definitely something worthwhile it alone will not make a great image so don't focus on that one aspect of your video replay chain.

    In the long term the FMJ-DV29 (or DiVA DV79) is probably the unit for you to go with and aim to partner it in the future with a decent Video Processor.

    Best regards

    Joe
     
  4. Nabs

    Nabs
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    Thanks for your comments. Glad to know my understanding was not too of mark.

    Now to wait first for flat screen technology to reach where I wish it too and buy a display first.
     
  5. pure_geordie

    pure_geordie
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    trying to understand it myself too, this is a good thread.

    Am I being stupid here but how do you tell which bit of kit does what, ie
    configure the DVD player do the scaling or how do you get the projector to do it? is there a switch or something that you flick on a dvd player or projector to tell IT to do the scaling, wether up or down.

    Cheers, I think I have reasonable kit although will be changing my DVD player for a 696 and the best I can get is 576i, i think thats the lowest.
    720p 576p and 1080i are all not good quality. 768*576i or something like that set on the DVD player and when connected to my projector it changes to 1076i*576i. Now I know I've probably got my resolutions a bit, lets just say out but I think you know where I'm comming from

    Cheers
     

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