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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

Re: Ad Blocker


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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,

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sounds difficult. How
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last bit of the last few
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logo, using a flash
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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
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with a TV card and
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switches channel or
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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

Re: Ad Blocker


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 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!
--
 "Men will never be free until the last king is strangled with the
  entrails of the last priest." (Diderot, paraphrasing Meslier)

Re: Ad Blocker


On Fri, 12 May 2006 11:03:40 GMT, GB

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I guess you have never worked for a commercially succesfull software
business.

Re: Ad Blocker


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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.
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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,




Re: Ad Blocker



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the logo for each station is in the same place?
so you really only need to examine a small number of pixels?


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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


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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.

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there isn't always _one_, I think you'll need to do edge detection
and if you see enough edges in the right locations you're seeing the logo,

locations will vary form station to station, many logos are transparent..

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with a TV card and
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switches channel or
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that's what drivers are for.

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many dos tools are free.

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figure on 4 or more neurons per pixel, I don't know where to get nneural
network hardware.

Bye.
   Jasen

Re: Ad Blocker


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


Re: Ad Blocker


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.


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[snip]

Elektor had a design in 2004 that worked on this basis:
http://www.elektor-electronics.co.uk/Default.aspx?tabid27%&year20%04&month=-1&art51%778&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.

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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

Re: Ad Blocker
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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.

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all that's needed for a vertical edge detector is a differentiator
(high-pass filter) and a pair of limit detectors. (one for light-to dark,
one for dark-to-light)

then you just need to spot edges that are in the right place.

if you get 90% or so you've probably got the logo.

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--

Bye.
   Jasen

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http://www.elektor-electronics.co.uk/Default.aspx?tabid27%&year20%04&month=-1&art51%778&PN=On
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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.

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http://www.elektor-electronics.co.uk/Default.aspx?tabid27%&year20%04&month=-1&art51%778&PN=On
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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

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http://www.elektor-electronics.co.uk/Default.aspx?tabid27%&year20%04&month=-1&art51%778&PN=On
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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...

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Ah, a library... that's that big sort-of shop thingy where they let you
borrow stuff - for nothing! - innit?  ;-D

Happy reading!

Chris.

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ads
http://www.elektor-electronics.co.uk/Default.aspx?tabid27%&year20%04&month =-
1&art51%778&PN=On
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logo


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.



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 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
--
 "Men will never be free until the last king is strangled with the
  entrails of the last priest." (Diderot, paraphrasing Meslier)

Re: Ad Blocker



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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.

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