Re: TV Charater Overlay - food for thought

[Wayne <wayne@xxxxxxxxxxxxxxxxxxxxxx>]

Thanks all!
Was wondering if this thing was an 'easy goer' but guess not... :(

A couple of things spring to mind though. Taking on board whats been
said about composite video, would a tv convert an rgb / svideo signal
>from
into) into composite video on a second socket? If this is the case then
(and a few leaps of faith are going on here) would it be possible to
'flip channels' by our new 'box' just while it displays the text - I
realize that the output of that would be composite video, but for 5
seconds (or some other manual response) or so it takes to acknowledge
the message is it so bad? It isnt as though your focus is on your movie
at this point. The other thing from that is getting this 'thing' to
release the channel and take you back to where you were before it
started or is this something thats variable depending on how the
manufacturers implement scart?

as a PS. did a 'Google' on the STV5730A chip Kieth talks about - to say
that this was a popular chip seems to be an understatement! although I
found this http://alternatezone.com/electronics/vtg.htm
which (about
half way down) suggests that this chip is now back in production! -
Would this be good news? (or fiction? - cant find it on a manufactures
web site) - although this then makes my original idea a little harder as
its now a case of working with chips rather than modules (no plug n play
:) )

Wayne.


Keith Doxey wrote:

>Quoting Des Gibbons <des@xxxxxxx>:
>
>
>
>>Wayne,
>>
>>
>>The problem with on screen display, is that nobody I know watches
TV using a
>>composite signal.
>>
>>
>>
>
>Unless they are watching Terrestrial through the TV's tuner but most TV
now
>would be from Tivo/Digibox/Cable/Freeview so valid point
>
>
>
>>There is no easy way of interlacing OSD onto a s-video or RGB
signal, (for
>>easy read cheap :)
>>
>>
>>
>
>Not quite true. No easy way for RGB but for S-Video you can switch the
Luma (Y)
>signal through the OSD device and get a monochrome overlay. The colour
of the
>picture may slip slightly to left or right whilst doing this but it may
not be
>noticable.
>
>Y IN ------ OSD ------ Y OUT
>C IN ----------------- C OUT
>
>
>For Colour overlay on S-Video you can use a couple of S-Video/Composite
adapters
>to drop down to Composite whilst overlaying the message and split it
back to
>S-Video afterwards but there would be noticable softening of the image
whilst
>doing this. eg
>
>NORMAL VIEWING OSD CIRCUITRY BYPASSED
>               /---------------------\
> Y IN---------/                       \----- Y OUT
>
>                Adapter-OSD-Adapter
>
> C IN---------\                       /----- C OUT
>               \---------------------/
>
>
>OVERLAY MODE S-Video-Composite-OSD-Composite-S-Video
>                ---------------------
> Y IN---------\                       /----- Y OUT
>               \                     /
>                 Adapter-OSD-Adapter
>               /                     \
> C IN---------/                       \----- C OUT
>                ---------------------
>
>
>As I say, it is possible but whether the results would be acceptable
depend on
>the individual. By far the best chip for this was the STV5730A which
could do
>RGB overlay but that is being discontinued with no replacement :-(
>
>Keith
>
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