[MPlayer-users] Re: which deinterlace filter

[Stefan Seyfried]

D Richard Felker III <dalias at aerifal.cx> writes:

> Maybe I misunderstand what you mean, or misunderstand analog/RF
> circuits, but I still fail to see how having a 60Hz clock source helps
> in making a TV.

the problem is not the clock source, the tv synchronizes itself with
the received signal. The problem is filtering the "ripple" off the
DC voltages. Until mid-1970s tv sets worked mainl with tubes, not
semiconductors. These had to be supplied with voltages of > 200 volts.
At such high voltages, you cannot just put in a big electrolytic capacitor
:-)
So you would get some variation in luminance in the picture. If this is
almost synchronized with the picture, you see (in the worst case) a darker
bar moving slowly over the picture, which is hardly visible (in fact, the
"pumping" was not that much). If you have it at 60-50=10Hz, you notice
the picture flickering at 10Hz, which is very noticeable, even if the
variation in luminance is small. 
The 60-59.94=0.06Hz are also not visible.

It was relatively unimportant how much effort had to be put into the
professional equipment of the tv studios when generating the frequencies,
but the television sets for the consumers had to be as cheap as possible.
And they still have to be :-)

About Japan having mixed 50/60Hz power, probably they just had more
expensive tv's or had to suffer from bad flickering :-)

regards,

    Stefan
-- 
 Stefan Seyfried, seife at gmane0305.slipkontur.de
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