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PAL to RGB

Discussion in 'Electronic Design' started by Alexander Pozhitkov, Jun 19, 2004.

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  1. Dear All,
    I have a source of a composite video signal which has PAL encoding. I want
    to decode it to RGB and synch signals. Does anybody know what IC is the most
    suitable for that?
    My numerous attempts to look it up in Philips, Texas Instruments and
    National Semiconductor totally failed: there is a lot of stuff for digital
    TV and DVD and weird decoders but nothing for my simple task.
    I'd appreciate any information.
    Alex.
     
  2. Tam/WB2TT

    Tam/WB2TT Guest

    Alex,
    To a first approximation you need to duplicate about 20% of a TV receiver.
    There is probably some IC that does all this. You need a synch separator,
    color subcarrier regenerator, and video processor. Also, possibly a sound
    detector. I am not an expert in this field, but have looked at some of these
    chips for other uses. Maybe somebody knows of a particular chip you can use.

    Tam
     
  3. **** Post for FREE via your newsreader at post.usenet.com ****

    Are you looking for the old analog Philips chips?
    The sync separator and 'castle pulse' generator was one chip,
    the decoder an other.
    You also needed a 64uS glass delay line, a about 0.57 us Y delay line,
    some tuned circuits, trimpot.
    Can give you some numbers for those (have to look it up).
    Probably very hard to get these days.
    Digital has advantages.

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  4. Hi Jan,
    Digital would be fine as well, I don't insist on the old analogue stuff.
    Texas Instruments has a bunch of digital decoders from PAL, NTSC and SECAM.
    This is actually what I want. But the output these decoders provide is not
    RGB, instead something I am not familiar with. Do you have any idea which IC
    of the digital decoders can sute my needs?
    Yours, Alex.
     
  5. Rich Grise

    Rich Grise Guest

    The problem is they have different scan rates. You'd have to have a two-
    port RAM, and some way to interpolate pixels.

    A little searching turned this up:
    TV Standard
    PAL NTSC
    Scan Frequency 50 Hz 60 Hz
    Number of Lines 625 525

    Video Resolution - ( H* = Horizontal, V* = Vertical )
    PAL NTSC
    DVD-Video 720 pixels (H*) 720 pixels (H*)
    576 pixeal (V*) 480 pixeal (V*)

    So you not only have different frequencies, but different pixel
    resolutions. (I don't know what a "pixeal" is.)

    Traditionally, this was done with a morphodite CRT with two electron
    guns, pointing from opposite ends at a plate in the middle. One gun
    would paint the raster on one side of the plate, and through some
    miracle of technology, the other gun would scan the raster at the
    other scan frequency.

    I'm sure it can be done digitally, but by someone much smarter than
    I am.

    Good Luck!
    Rich
     
  6. **** Post for FREE via your newsreader at post.usenet.com ****

    Hi, those chips have digital component out likely, you need a decoder to RGB,
    look for example here for one:
    http://www-us6.semiconductors.com/pip/SAA7111AH.html
    If you download the datasheet you will see an example (page 40 of the pdf)
    that uses a simple 74hct574 latch to make 8 bits R G and B.
    There is a multitude triple 8 bit DAC for RGB video on the market.
    It is a rather old chip.
    PAL delay line is digitally build in.
    You will need a micro processor to program the registers.
    Have not used this chip, just result of typing
    'philips PAL RGB digital datasheet decoder' in google.
    JP

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  7. Dear All,
    Hi Jan,
    This chip sounds better! In fact, my problem is the following, maybe you
    have a better idea than mine. I have a European VCR and bunch of tapes. All
    of this is of course PAL. I kind of want to watch them from time to time. I
    was thinking to decode the composite video which you can get from the VCR
    and feed RGB and synch to a computer monitor. Yes, sounds clunky, a
    multisystem VCR and/or TV would solve the problem, but these beasts are very
    expensive for watching just these tapes. Any better idea?
    Alex.
     
  8. **** Post for FREE via your newsreader at post.usenet.com ****

    Aha, if you have a European VCR, then it likely has a SCART connector
    (On multipole on the back).
    And it that case it may well have already RGB and sync out on that.
    It is sort of a standard over here.
    YMMV
    Did you google for PAL decoder? If you are into electronics get an old scrap
    PAL TV, better even, here they sell for 190 Euro (36cm)...
    Websearch?
    There is also an other way, get a video capture card, digitize the PAL to
    DivX (get free codec from www.divx.com) 352x288, then throw away the VHS.
    You can play that on the computer monitor, process it too.
    Does any of this make sense? I digitized all my VHS to DivX about 3 years ago.
    JP

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  9. Tam/WB2TT

    Tam/WB2TT Guest

    ......................................................
    Alex,
    Just get a video capture/TV tuner card for your PC. They sell for U$ 50 -100
    over here; so, price in pounds should be about the same, since you people
    pay about a 1.5X surcharge on everything.

    You might want to check out www.atitech.com if they make a PAL card. NTSC
    is sort of trivial since 640 x 480 60 Hz VGA was based on NTSC. My offhand
    guess is that PAL would require 800 x 600 75Hz monitor settings.

    Tam
     
  10. Great, this makes sence. In line with the Jan's recomendation digitization
    by a computer is much simplier than bothering with DIY decoders :)
    Alex.
     
  11. Tam/WB2TT

    Tam/WB2TT Guest

    Hi Alex,
    I just realized I had placed you 3000 miles in the oposite direction. If you
    get a PAL video capture card, make sure it works with the refresh frequency
    of your PC's video card and monitor. I know that neither my card, nor
    monitor will do 50 Hz. I would hope that the thing works at 75, or maybe 100
    Hz.

    Tam
     
  12. This is not needed, I can view PAL on a 85 Hz PC in 800x600 (now).
    So can you view NTSC on a 85Hz V freq monitor...
    In the modern world in 95% of the cases, there is no V sync to the incoming
    video.
    The way this works is framedrop (every now and then).
    It is true that using 100Hz for PAL is better, but hard to see the difference here.
    It is even more true that getting a video card that supports this sync is better,
    but there are only a few (for Linux, not even sure about win).
    Anyhow the result will be usable with an odd frequency.
    I have made PAL animation in 1280x1024 25 Hz progressive, playing on a 1280x1024
    85Hz monitor...
    Play with it :)
    JP
     
  13. Tam/WB2TT

    Tam/WB2TT Guest

    This is sort of what I was hoping was true. BTW, I think Alex's original
    proposal would have required a 50 Hz interlaced monitor. We all missed that.

    Tam
     
  14. But what if I digitize the video stream using this video capture cards and
    store on the hard disk, will it still preserve the characteristics of the
    European standard? I think after processing I should be able to convert it
    to any standard and play on any monitor hooked up to the computer, isn't it?
    Alex.
     
  15. Tam/WB2TT

    Tam/WB2TT Guest

    That is what Jan is saying. The information is still coming in at 25 frames
    /50 fields per second. So, something in the software must know how often to
    update the data for display. I don't know how the internals of display
    driver software work. It might just "know" that. Conceptually, a 75 Hz
    refresh should be simple; each frame would be displayed 3 times in
    succession. Try to find likely capture cards, and see if you can download
    their manuals. I think ATI manuals are available on line.

    Tam
     
  16. Ryan

    Ryan Guest

    Something like this should fit the bill:

    <http://www.averlogic.com/video_converter/AL250.html>

    You can purchase the "cheesebox" evaluation board for $150 USD I think.

    Ryan
     
  17. Yes, 25fps
    In theory yes, in practice you need software for that.
    I have not done any PAL to NTSC conversion yet on the PC.
    If you have a 19inch monitor watch the PAL on the monitor.
    There has been a thread on PAL to NTSC conversion in rec.video.desktop a
    little while ago, check www.dejanews perhaps.
    In my case I would just write some plugin for Linux transcode if I needed it
    and could not find anything perhaps (maybe it already exists).
    One would have to repeat frames every now and then (and keep the sound
    the same), have not tried.
    Ah, it exists in transcode:
    http://www.theorie.physik.uni-goettingen.de/~ostreich/transcode/
    From the manual:
    fps - convert video frame rate, gets defaults from -f and
    --export_fps
    fps was written by Christopher Cramer. The version
    documented here is v0.2 (2003-08-10). This is a video
    filter. It can handle RGB and YUV mode. It can be used
    as a pre-processing or as a post-processing filter.

    options: <input fps>:<output fps> example: -J
    fps=25:29.97 will convert from PAL to NTSC If
    no options are given, defaults or
    -f/--export_fps/--export_frc will be used.


    You could try using the NTSC video out of the graphics card on a normal NTSC TV,
    but that of cause gives quality loss.
    But simplest solution.
    JP
     
  18. **** Post for FREE via your newsreader at post.usenet.com ****

    Yes, 25fps
    In theory yes, in practice you need software for that.
    I have not done any PAL to NTSC conversion yet on the PC.
    If you have a 19inch monitor watch the PAL on the monitor.
    There has been a thread on PAL to NTSC conversion in rec.video.desktop a
    little while ago, check www.dejanews perhaps.
    In my case I would just write some plugin for Linux transcode if I needed it
    and could not find anything perhaps (maybe it already exists).
    One would have to repeat frames every now and then (and keep the sound
    the same), have not tried.
    Ah, it exists in transcode:
    http://www.theorie.physik.uni-goettingen.de/~ostreich/transcode/
    From the manual:
    fps - convert video frame rate, gets defaults from -f and
    --export_fps
    fps was written by Christopher Cramer. The version
    documented here is v0.2 (2003-08-10). This is a video
    filter. It can handle RGB and YUV mode. It can be used
    as a pre-processing or as a post-processing filter.

    options: <input fps>:<output fps> example: -J
    fps=25:29.97 will convert from PAL to NTSC If
    no options are given, defaults or
    -f/--export_fps/--export_frc will be used.


    You could try using the NTSC video out of the graphics card on a normal NTSC TV,
    but that of cause gives quality loss.
    But simplest solution.
    JP



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  19. Tam/WB2TT

    Tam/WB2TT Guest

    Jan,
    Seems like no matter what, the capture card need to know it is getting a PAL
    signal. Not just the frame rate, but the color subcarrier is at a different
    frequency. And of course, there is the phase alternating thing. Once the
    software knows it is PAL, it should know everything it needs to know.

    Do you know what the card does about the fact that the input signal is
    interlaced? My guess is that it just puts two fields together, and calls it
    a frame.

    BTW, I will be looking at video capture cards myself. Want to put a bunch of
    camcorder tapes on a DVD. All NTSC, of course, so there is not the added
    complexity of scan conversion.

    Tam
     
  20. **** Post for FREE via your newsreader at post.usenet.com ****

    There are basically 2 sorts of cards.
    What camcorder do you have? These sometimes a have firewire interface.
    If it is a digital one then it is DV format (sort of like jpeg pics for each frame).
    So, now about the capture cards.Thre are hardware mpeg2 capture cards available
    now that should handle the interlaced video (DVD is also interlaced) so no need
    to change anything (but of cause check it is PAL capable!).
    Then there are 'TV cards wit ha digitizer, that output YUV directly, or, if
    you select a codec (talking windows now) a compressed format such as DivX (as a
    Avi stream).
    Most common used program in MS widows circles is virtualdub (free), you can
    do some cutting with it (there is a mpeg2 version).
    Anyways if you get a mpeg2 card it will likely come with capture software,
    some DVD players do too.
    In the worst case you need 3 cards hehe, one firewire, one mpeg2 hardware,
    and one (TV)digitizer type...
    So, you work it out, best is to ask in rec.video.desktop 'which is the best card',
    so many people so many opinions, I am not venturing there.
    I digitized my VHS with the ASUS VT7700 I think it is, in MS win, directly in DivX,
    325x288 (so that way you do not have to de-interlace).
    This cause a bit of quality loss, but the videos were already pretty worn out..
    Still in DivX I can get one hour on a CDR at 1500kbps with good quality.
    And no wear and tear as with the VHS tapes.
    If you seriously go DVD, try 640x480 interlaced, as it is a DVD standard,
    and use one of those hardware mpeg2 encoder cards.
    Lets us know how it worked out too please.
    JP

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