Assuming this means NTSC:
|NotTaR of Television Sets : Displaying computer video on a TV
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- You need to convert RGB to NTSC - there are single chips for this. Try
Sony, Philips, Motorola, and others. These will combine the R, G, B,
H sync, and V sync into a single composite video signal using a minimum
of additional components.
- You need to match the scan rate to NTSC - 15.734 kHz horizontal. Even
basic VGA is twice this - 31.4 kHz. If your video card can be programmed
to put out interlaced NTSC rate video then this is easy. If not, it is
more difficult. If you want to use anything higher res than VGA, it is
a very non-trivial problem requiring the construction of a scan convertor
which includes a video A/D, full frame store, interpolator/readout timing,
video D/A. Unless you are an experienced digital/analog designer, you
really do not want to tackle any of this.
For the special case of VGA->NTSC, you may be able to get away with just
storing a single scan line since the horizontal frequency is (almost)
exactly twice the NTSC horizontal of 15.734 kHz. A double buffer where
one buffer is storing while the other is reading out at approximately half
the VGA pixel rate should work. With appropriate timing, even lines become the
even field for NTSC and odd lines become the odd field (I may have this
backwards). It is still not a trivial undertaking. Also, keep in mind
that the quality you will get on NTSC will be poorer than the VGA due to
fundamental NTSC bandwidth limitations. Also, flicker for line graphics will
be significant due to the interlacing at 30 Hz. Even this is a non-trivial
The requirements for PAL are very similar. For 625 lines systems, the
800x600 is the format that most closely matches the TV resolution.
You can also buy little boxes to do this. Quality is general not great
as you are seriously limited by NTSC/PAL and the VCR. Except for
presentations on existing TV rate equipment, it is probably not worth
the effort. This is totally useless for any serious computer applications.
For professional presentations, modern video projectors are available that
use high resolution LCD panels and real-time scan conversion. However,
they are still relatively expensive).
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