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Discussion in 'Hobby Electronics' started by Dave Goldfinch, May 12, 2006.

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  1. A recent letter to Silicon Chip suggested using the TV station logos
    as a trigger for an ad blocker. (the logo is not present when the ads
    are broadcast).

    While I recognise that my chances of getting this to work are slim to
    non existent, I think it will be educational to try.

    I found a data sheet for the LM1881 sync seperator and was pleased to
    find a description & circuit of a video line selector in the
    application notes. See http://www.datasheetarchive.com/.

    I have built this but am having didfficulties getting it to work. The
    problem appears to be that the Vertical Sync output 'disappears' at
    the input to the flip-flop formed by the 74C00.

    I can see the pulses on pin 3 of the LM1881, but on the other side of
    the .001 cap connecting to pin 1 of the 74C00, I only see a steady 5V
    which comes from the 2K resistor connecting this pin to Vcc. The
    resistor is paralelled by a diode - type unspecified, I used a 1N4148.

    Has anyone here built this circuit ? Any suggestions ?

    TIA

    Dave
     
  2. sam

    sam Guest

    I haven't seen the letter you mention but, as you say, doing it in hardware sounds difficult. How
    are you planning to do it? I guess that you'd need to capture and store the last bit of the last few
    lines in a frame then use digital image processing techniques to detect the logo, using a flash
    convertor and memory and a CPU.

    Have you considered doing it in software with existing hardware? Perhaps a PC with a TV card and
    software that periodically checks the captured image for the logo, then switches channel or
    interfaces to the remote control or whatever.

    Eitherway, a neural-network detector might be fun to try.

    Cheers,



    Cheers,
     
  3. Guest

    I looked into this about 20 years ago. Back then, most of the TV
    stations fade to black for a brief time, before and after ads. Perhaps
    this may be a simpler method.

    Trevor Wilson
     
  4. Yes, that is basically the approach I had in mind, except for the
    image processing bit - I am hoping to digitise a line or lines and
    look for a value that changes as the logo appears/disappears

    I had a look at doing it in software but you really have to get 'down
    & dirty' to process the image & Windows puts up massive barriers
    between you & the hardware. You could, of course look at doing it in
    DOS, but then you can't get drivers for available capture hardware,
    and I don't have the development tools. I do like the idea of a neural
    network though - I will have to do some more research.

    Dave
     
  5. GB

    GB Guest

    Why on earth would you lower yourself to doing it with *any*
    microsoft or microsoft-derived product when there are any
    number of unix and unix-like operating systems available completely
    free of charge that will give you direct access to all you need to
    develop working code, and numerous libraries that will do much of
    the work for you.


    GB, I have problems comprehending the ongoing use of microsoft
    products in business, but this, this is just... speechless!
     
  6. I guess you have never worked for a commercially succesfull software
    business.
     
  7. sam

    sam Guest

    I think that the logos are a sort of watermark thing; the logo pixels are reduced in intesity
    compared to the underlying image pixel. They're not of a fixed intensity. This could make detection
    pretty tricky, especially as the underlying image could be changing too.

    Edge detection followed by logo-specific detection might be the go.
    As someone else has pointed out, using an Open Source unix, most likely linux, is a much better
    option for this sort of project IMO, especially if it's dedicated hardware. I can elaborate if you'd
    like.

    I reckon that a reasonably small, bog-standard back-propagation neural network would do the job. I'd
    use a sampling of the edge detection data for the inputs. You'd probably have to train a net for
    each logo, but then again maybe not, then again the net might take care of the edge detection too.

    Cheers,
     
  8. rowan194

    rowan194 Guest

    One thing that might put the brakes on your hardware idea - at least
    one station slowly moves their watermark within a small area in order
    to avoid plasma burnin. You'll probably need more processing power to
    figure it out.
     
  9. the logo for each station is in the same place?
    so you really only need to examine a small number of pixels?

    Well, how do you add a watermark?
    Is it just a signal mix
    Can you detect that signal in the logo area?

    would it be a hue/saturation/?? difference

    or is it something simple as 50% of pixels become a set colour over the
    area. that should be easy to detect

    there was a package called motion (since renamed) that was designed to
    detect movement in a cam and start recording. It did this by % change in
    scence. I was thinking it might just give you the shell of the program
    and you just change the analysis to report what happens in the logo area.

    Just some idea. Not my area.
     
  10. chris

    chris Guest

    [snip]

    Elektor had a design in 2004 that worked on this basis:
    http://www.elektor-electronics.co.uk/Default.aspx?tabid=27&year=2004&month=-1&art=51778&PN=On

    It used an embedded micro with a learning IR tranceiver to transmit a
    'pause' signal to the VCR.

    Would require modification to use in Aus because it looked for the logo
    in the top 1/4 of the picture (as in Europe, aparrently).

    FWIW.

    Chris.
     

  11. Hi Chris

    Thanks for that - it appears to do exactly what I would like.

    At least this suggests that it is possible to use the logo, not just a
    hopeless dream.

    Dave
     
  12. Mark Harriss

    Mark Harriss Guest

    If you digitised the image then there are some math functions
    that could look at that corner of the image and pick up a sudden
    fixed change in the value from one pixel to the neighbouring one
    caused by going from a non watermark area to a digital watermark.

    The key would be to look for a relatively fixed number of pixel
    transitions changing by a fixed amount up (whiter) and almost the
    same number of transitions going down by the same fixed value for
    every scan line.

    You would have to play with tolerances a bit but it should work.
    The hardware would be complex though, possibly a PC and frame
    grabber.
     
  13. GB

    GB Guest

    Forgive me to leaping into this thread so late, but as a matter
    of interest, Phillips recently gained a patent (In the US I
    suspect) for a system that would force punters to watch advertisements
    by disabling pause/ffwd/channel-change/etc functions for the
    duration of the advertising.

    Notwithstanding that the company made noises about their intent
    being to lock it up to protect anyone from actually doing it,
    there were there to-be-expected round of "patent on stopping people
    from buying Phillips televisions, etc, etc" whinges.


    All the Free Software/Open Source Software folks who are involved
    in authoring PVR type code took a very different view. Theirs was
    "Thanks Phillips, for creating a system that tells us reliably
    when the advertisements start and end"!!!


    GB
     
  14. chris

    chris Guest

    I have the original article if you're interested.

    Dunno if I have the CD (with article in PDF format) for that year - I'll
    have a look. Otherwise I could probably scan it for you - if you have no
    deadlines to meet (read: it may take some time!) ;-)

    Still for the price of ~1 quid from their website...

    Chris.
     
  15. Thanks for the offer. I went & had alook at their website & was about
    to download the article but was put off by their paying arrangenments
    - they seemed to want far too much personal detail - I am probably
    just a bit paranoid about disclosing card details over the net, but
    this really seemed over the top. Have you used this service ?

    Fortunately the WA library service gets Elektor & so I have just been
    into town & got a copy of the article - will sit down now to read &
    digest.

    Dave
     
  16. chris

    chris Guest

    Since I've been getting the mag for a few years now, I haven't had to,
    no. It is annoying when they want all those details, & there's always
    *some* risk entering card details...
    Ah, a library... that's that big sort-of shop thingy where they let you
    borrow stuff - for nothing! - innit? ;-D

    Happy reading!

    Chris.
     
  17. Mr.T

    Mr.T Guest


    Yes, but you would miss the start of each segment as the logos are often
    slow at coming back.
    Surely the FF control is a lot cheaper anyway.

    MrT.
     
  18. David Segall

    David Segall Guest

    Apart from the possible inconvenience of waiting for a new card, what
    is the risk? If someone uses your credit card fraudulently the issuer
    will bear the cost. In any case, there is probably far less risk of
    that than someone obtaining the details from the hard copy you used in
    a local restaurant.
     
  19. tim

    tim Guest


    There already is an Ad blocker. The ABC.

    Cheers
     
  20. GB

    GB Guest

    They've got more ads (albeit for themselves) than the
    rest of 'em put together!


    GB, and every day I walk past about a dozen of 'em standing out
    the front having a fag^H^H^Hsmoke. I want my eight cents back,
    damnit!
     
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