Hello.
Maybe I haven't exactly described the video source. It is really the
problem of Gain Control.
I have _extrenal_ multiplexr ( and chip has it's own too - internal )
so I have:
cameras:
1: --- |
2: --- |M ---- [TV input of chip ] ---
.. --- |U
8: --- |X
So i receive only one frame at the moment.
When chip detects blank frame it increases brightness ( not at the
moment, it lasts some frames ).
So it is really AGC.
Regards,
Dmitry.
P> On Thu, 13 Sep 2001, Dmitry Alexeyev wrote:
>> Hello.
>>
>> I have BT878 card and external multiplexer with several monochrome cameras
>> connected to it. If one camera is off ( blank screen ), bt878
>> automaticaly increases brightness, so I can see nothing on frames from
>> other cameras.
>> How can i turn off AGC ?
>>
>> Dmitry
>>
P> Seems your problem is the multiplexer not the AGC.
P> If properly clamped to black level AGC will probably
P> no longer interfere.
P> This of course requires minimum expertise to
P> clamp the multiplexer input to black level
P> when camera is off (using a capacitor, resistor
P> or combination, after analysing the input circuit).
P> However, if you have such ability it must be
P> pretty simple and "safe" once it's just a simple
P> clamping. (clamping activation via camera power)
P> But with today VLSI "closed source" trend things
P> simple like this may even be impossible. :-(
P> Open source hardware too will be great....
P> schematics, information access... or better
P> put the closed hard crap in trash together
P> with the closed source soft too. ;)
P> No need to mess the AGC that seems to be not
P> the cause but just the symptom of a floating
P> input signal.
P> Hope this helps.
P> --
P> HOM: http://www.momentus.com.br/users/hook/
P> GPG: http://www.momentus.com.br/users/hook/GPG-PauloCastro.asc
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