🚀 go-pugleaf

In article: <830283694snz@longley.demon.co.uk>  David Longley <David@longley.demon.co.uk> writes:
><snip>
> > > > I was more interested in capturing 'still' images than 'movies'. I have
> > > > some video tape with pictures of my now deceased nephew on them, and I
> > > > would like to capture some images of him.
> > > >
> > > >
> > > I think you'll find the quality disppointingly poor...
> > 
> > Is this due to the quality of a single video frame?
> > 
> > What sort of device would provide an acceptable result at a reasonable
> > price?
> > 
> I'd be interested to hear what others say on this, but VHS is not as good
> as broadcast, and when I've captured VHS to disk using a Miro DC1 card, I
> can't say the quality has anyway matched say a digitized 35mm camera shot
> as a slide. 
It won't get near to a 35mm slide. Look at the Photo-CD standard. 18mB, for
a single 35mm frame. Compare this to under 1mB, for the best that an S-VHS
video frame, can approach.

> 
> I'd be grateful if someone who has the figures could explain in detail how
> the image loss comes about from say VHS --> half PAL capture --> MPEG
It is suprising however, what can be done. You have both 'bandwidth' and
nominal 'resolution'. Standard TV, uses 312.5 lines per frame, and a
bandwidth such that you should be able to resolve about 700 points/line.
VHS, limits the bandwidth to the point, where you can only guarantee
about 3-400 points/line. S-VHS, or High-8, give near to broadcast levels,
Betamax, was significantly better than VHS, but not quite as good as S-VHS.
but each successive record/playback transfer degrades performance.
Cheap 'single-frame' grabbers, can give you a realistic 320*200, from a
VHS video frame. This will reproduce, as a _very acceptable_ picture
at 3*2 inches, or 4*3. If you try to enlarge this much further, it will start
to look very poor. S-VHS video, grabbed with a really good card, can
reproduce at 5*4 inches, and look remarkably good. The first thing 
to degrade, is the picture colour, and a bit of care, with one of the
picture editing packages, can help here. The human eye, accepts far
lower resolutions, in a moving image, than in a static image, effectively,
starting to 'look for detail', as soon as the image stops. This is why
the relatively poor resolution of a VHS recorder, is acceptable, but the
same image looks very poor stationary. A 'grabbed' frame, tidied up,
and displayed in perhaps 1/4 of a 14" monitor, can look quite OK.
Look around, for the original Videologic 'captivator', or the Rombo
frame grabber. Both work quite well, if you do not require to grab fast
movies. The latter 'Captivator Pro', requires a video card, with the
'VMC' connector, and is really designed to grab movie information.
'Vine', in Kent (Margate I think), used to also do some effective
grabbers. 'Up-market' grabbers, can link the information from two
successive video frames, to increase the number of lines available
over 312, but anything from a VHS camera, only has about 200
useable lines available. S-VHS, has usually double the resolution
in the camera, and with the better recording bandwidth, can give
about 500*400 points with the right grabber. Many grabbers can
take more points than this from the incoming stream, but all this
does is use more disk space, without any increase in final
resolution. You have to also seriously consider what output device
you are going to use. A laser, or inkjet printer, may have a nominal
300*300 point resolution, (or more), but this is only of on/off dots.
To print a picture, patterns of these dots are used to reproduce
various intensity levels, and this is where the big difference exists
in the printing industry, where quite high quality photographs are
only printed with a 'mask' of 100 to 120DPI, but each 'dot', can be
itself, any of many thousands of different sizes, to give good
colour/intensity reproduction. A 300 DPI laser printer, will only
be able to give a reasonable number of different dot patterns, at
30-45DPI, which is why pictures printed this way, look relatively
poor. Modern 'typesetting' machines (not really, but photo-
typesetters), function just like a laser printer, but at 4 to 8 times
the resolution. To get good photo quality colour printing, look
for devices such as 'dye-sublimation' printers, that can produce
300*300DPI images, but with hundreds of different die intensities
at each point.
Hopefully, the original poster, will be able to produce some reasonable
small snapshots from his video, but shouldn't expect to acheive
miracles.

Best Wishes

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