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SubjectVHS backups (Re: NEWSFLASH! Linux ported to Commodore VIC-20!!)
Date
On 	Tue, 15 Sep 1998 03:05:26 -0500 (CDT), Oliver Xymoron said:
> The spec I gave - 320x200x8 at 15 frames per second - is the resolution of
> an old Fisher-Price video recorder that recorded on audio tapes. NTSC
> resolution is nominally ~640x~484x~18bpp(1) at 30 frames per second so my
> original estimate was allowing for more than a 16x degradation in quality,
> or looked at another way 16:1 ECC. VHS is bad, but not so bad that that
> wouldn't work.

You get a horizontal resolution of about 250-300 in the luma signal when you
record on VHS. The chroma signal is much worse and isn't worth bothering
with. To put it another way, the bandwidth of the VHS luma signal is about
2.5 MHz so base your figures on that. However, whatever encoding you use
will obviously have to include the correct horizontal and vertical sync
signals to avoid confusing the recorder and you will want to avoid the
head-switching noise which generally occurs during vertical retrace.

However, I have a feeling that some of the processing used in VCRs has
the effect of merging adjacent lines somewhat, so you might want to
trust only every alternate line.

imc

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