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Video Processing

Discussion in 'Projectors, Screens & Video Processors' started by gbrown, Aug 18, 2004.

  1. gbrown

    gbrown
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    Prior to getting my Lumagen HDP I read up on de-interlacing algorithms and I think I've got most of it straight.

    I was concerned that since I was feeding the HDP with an analog signal from my DVD I was adding an extra A-D conversion, but I realised that since I will be feeding my Plasma with DVI in fact the scaler is only doing the A-D that the plasma would have to do. Is this right?

    Just want to be sure that my HDP was a good investment! :D

    Now I have a better idea of what 3:2 and 2:2 pulldown and bob and weave, etc. mean it leaves me with a lot of un answered questions. The main one is how do you find out what algorithms are used by what equipment. Since they can make a big difference to the picture quality, it seems important to know.

    Another question is how do you find out what encoding has been used on a DVD. This seems important to determine the best mode to output the data. If a disc stores progressive data then I guess Prog Scan is best, but if the data is interlaced then I guess it is best to output interlaced and let the HDP de-interlace, since that is what it is best at.

    What happens if progressive encoded material is output as interlaced, is each field just the full frame as stored on the disc. How will the lumagen handle this?

    I look forward to playing with my kit when it arrives, and finding out if these questions are as important as they seem! :thumbsup:

    Cheers,

    Geoff
     
  2. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Geoff:

    Re: interlaced out prog out. My undestanding is that it doesn't matter how it's encoded on the disc. At present all mpeg decoders in players output interlaced signal which is then de-interlaced internally for prog output or fed out interlaced for processing down the line. At least that's what a major DVD player manufacturer told me.

    The style of algorithm is important but so is the implimentation so two motion adaptive per pixel algorithms may not be of same performance.........

    Easiest way to find out what sorts are used by different manufacturers is probably to ask them.

    You are correct that instead of the plasma doing A to D it's now happening in the scaler. Which will have superior AtoD and associated crcuits for this job.

    Gordon
     
  3. gbrown

    gbrown
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    > Re: interlaced out prog out. My undestanding is that it doesn't matter how
    > it's encoded on the disc. At present all mpeg decoders in players output
    > interlaced signal which is then de-interlaced internally for prog output or
    > fed out interlaced for processing down the line.

    I read something that said much the same. The question therefore just moves up the chain to the decoder chip. I guess if the content is progressive the algorithm just puts out each interlaced field using a complete frame. When the lumagen de-interlaces this I hope it doesn't degrade it, or perhaps it has a way of detecting it.

    If it is true that all DVD's decodes put out interlaced signals then feeding a scaler with interlaced would appear to be a better bet than using a prog feed, where extra messing about may have been done.

    Cheers,

    Geoff
     
  4. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    Do you mean when outputting interlaced or progressive?
     
  5. gbrown

    gbrown
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    > Do you mean when outputting interlaced or progressive?

    Interlaced.

    You said "At present all mpeg decoders in players output interlaced signal"

    My comment was then "The question therefore just moves up the chain to the decoder chip. I guess if the content is progressive the (decoder) algorithm just puts out each interlaced field using a complete frame."

    I am curious why all the decoders should ignore the progressive flag and just treat it as interlaced. I wonder what this does to the PQ, but I guess they only do it because it has little effect. Do they just output the whole frame for each field. Then what happens if these are de-interlaced for progressive output. Combining 2 identical fields could give no errors, but it must depend on the details of the algorithm used.

    I get the feeling that the issues involved in de-interlacing and 4:2:0 upscaling to 4:2:2 (or 4:4:4) are very complex and the details of the algorithms used are not published so it is hard to be sure when it is done properly. Therefore it becomes difficult to say that it is better done in any particular DVD player, display or an external processor without subjective testing.

    I suppose it boils down to a question of faith, that the video processor only exists to do a better job of de-interlacing and scaling so therefore it must use better techniques. I look forward to testing mine out and seeing it for myself! :D
     
  6. Gordon @ Convergent AV

    Gordon @ Convergent AV
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    OK:

    It's not possible to output a whole frame as an interlaced field. That would be progressive not interlaced. The player creates the two interlcaed fields form the progressive frame and sticks them out. For NTSC/R1 source material it also adds in the repeat field every fifth field to create the 60 required from the 48 stored(2:3 sequence).

    Some prog scan DVD players actually do look at the flagging of the data to de-interlace the material back to progressive. Unfortunately this data is often not there or is wrong.

    It's all a bit weird to me. There is a book (BIG AND THICK) called DVD De-mystified that should give you all the data you want. It's one of those books that I look at though and just can't bring myself to read. Perhaps I'll get it fo rmy next long haul flight!

    The most robust way to do de-interlacing is to look at the actual picture iinformation in each field and process it. That's where you get differences in ablity to recognise what is film, what is video and what is a bad edit etc.

    Hope this is a little use.

    http://www.amazon.co.uk/exec/obidos...1960/sr=2-1/ref=sr_2_27_1/026-8286034-5715649

    Gordon
     
  7. gbrown

    gbrown
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    Thanks for the book reference. Like you say, interesting but at that level of detail perhaps a good cure for insomnia. :rotfl:

    I had a quick look at the Descaler open source project last night, perhaps I'll have a look at some of the source code, it might give some insights. Or perhaps I'll just wait for my kit and spend the time watching movies instead. :)
     

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