[mythtv-users] OT: White shadow

[Justin Hornsby]

The effect is known as 'bearding', possibly also referred to as
'bleeding' (which is more often than not associated with colour
'runs').

Bearding can be caused by oversaturated colours or luminance
(brightness) - the symptoms of which become apparent on CRT displays
because of limitations in the high voltage circuitry driving the
electron guns (more than likely the power supply and/or HT driver
circuits).

Broadcast & production video signals are usually very well regulated
between 'safe' limits (known as black level & peak white level) to
ensure effects such as bearding do not occur in normal circumstances.

For a more detailed explanation I recommend you read a book about
video signals or find a guide on the internet (e.g.
http://www.tek.com/Measurement/App_Notes/25_15215/eng/25W_15215_0_PartI.pdf).

It's more than likely a good idea that theme designers follow the
'broadcast safe' rules for colour & luminance - I don't (yet) but I
plan to in future.

Another factor you've probably not considered is that the TV encoders
on most VGA cards are more than capable of producing out of spec.
signals which some TVs can't cope with.  The only way to verify how
'in spec' your video card is would be to use a known good test signal
& either an oscilloscope or a vectorscope if you have access to one (I
do but I've never checked the quality of any VGA TV out signal).

All interesting stuff huh?

Regards,
Justin.
-- 
Justin Hornsby
Creator of ProjectGrayhem, blootube and neon-wide themes for MythTV
email: justin(dot)hornsby(at)gmail.com
web: http://www.juski.co.uk