On Sun, 27 Jan 2002, David Fries wrote: > I also have been experimenting with capture with mp1e and what I > haven't figured out is what the highest capture resolution is. I > would have to thank Brian J. Murrell for mentioning it on the list, > once I found it, it didn't take any time to get it installed and > working (compared to about all other aspects of the tv tuner). When I > capture at say 640x480 it is interlaced (and my K6-2 300Mhz can't > compress it real time). xawtv also captures captures interlaced > images no matter what and zapping only seems to want to capture at > 320x240. The tv card box claims 1500x1125, I know TV doesn't have > that resolution, but I wouldn't expect it to be interlaced. I'm > capturing cable or from VCR tapes. Is there anyway I can have the tv > card tell me how many lines of resolution it is pulling in? Hi, In the vertical direction, TV has 576 "active" lines (PAL), 480 lines (NTSC). This is split over two fields as you know. In the horizontal direction its hard to quote a resolution in pixels. The transmission is analogue, and the encoding gives the luminance (black&white picture) and the chrominance (colour) different resolutions. For a PAL encoded composite signal, there's around 4.3MHz bandwidth available for luminance before it starts to interfere with the chrominance subcarrier. Active portion of a horizontal scan line is about 52us. So resolution will be about 450 pixels by my calcs. Higher resolution can be driven, but colour artefacts will tend to appear. For NTSC the colour subcarrier is 3.58MHz, active line time around 53us, so resolution around 370 pixels. For s-video, bandwidth available is higher due to the fact that the chrominance is separate and so interference is avoided. Assuming generously 6.5MHz bandwidth, that's about 680 pixels of resolution. If you are capturing from VCR, there's only a couple of MHz of luminance bandwidth, probably horizontal resolution will not be much more than 300 pixels. And vertical resolution is no more than 200 lines or so for standard VHS. Its not quite so simple as these calcs, of course. In practice my experience (with PAL, and capturing composite video, playing back to a TV) is that a 720x576 capture is for sure sharper than 352x288. But 352x288 looks much better than you might expect. One thing to be aware of - you will need a high bit rate to capture your VHS tapes. The poor quality playback brings lots of noise, dropouts etc. These are hard to encode. So use a low resolution and a high bit-rate. Steve
