Thanks, that is generally how I recall it and much more.... > -----Original Message----- > From: opendtv-bounce@xxxxxxxxxxxxx > [mailto:opendtv-bounce@xxxxxxxxxxxxx]On Behalf Of S J Birkill > Sent: Friday, December 15, 2006 2:33 AM > To: opendtv@xxxxxxxxxxxxx > Subject: [opendtv] Re: PAL; 405 line pictures > > > Walter Bruch and his PAL team at Telefunken tackled the major > shortcoming of NTSC: hue errors due to distortion in video amplifiers > and modulators. It was the cumulative phase errors through dozens of > amplifiers in a TV studio complex, hundreds in a terrestrial > distribution chain, plus transmitter modulators and receiver demods, > essentially non-linear circuits, that spoiled NTSC. It's easy to > forget that before satellite distribution in the 1970s, Americans > seldom saw accurate color on their screens. > > Differential phase was the killer. Those non-linear stages > systematically shifted chroma phase according to the instantaneous > luminance level (above black, burst reference) the chroma was riding > on: flesh tones took the brunt, yielding NTSC's traditional green, > orange or purple faces; hence the system's need for a 'hue' control. > PAL eliminated this, converting phase error to a small amplitude > error -- diff phase distortion looked just like diff gain, > introducing only a slight desaturation at the higher luminance > levels. One less knob on the set. > > PAL's line-wise alternation of the V (R-Y, give or take small > differences in scaling, matrixing and gamma-correction) chroma > component's modulation phase, serves to correct chroma phase errors > by optical (simple PAL, long obsolete) or electrical (delay-line PAL) > averaging. The delay-line method halves vertical color resolution, > which then matches (again approximately, so don't take me to task on > the numbers -- this is from memory) its band-limited horizontal > resolution. NTSC retains the higher vertical color resolution -- > that's the *only* loss from PAL coding. In fact there's a slight > collateral gain: the phase switching dithers the CSC pattern, making > for a less visible diagonal 'dot crawl' in saturated picture areas; > CSC notch filtering in the receiver could be relaxed a little. > > ['Composite video over telephone lines' is misleading: 625-line video > distribution in the UK (for instance) was from its very beginning > (1964) via 5.8-MHz equalized co-axial cable within studio centers and > across cities, and via 2GHz or 7GHz FM microwave links between > studios and transmitters. Even in the 405-line days when video > bandwidth was 3MHz, STLs on the main distribution backbone were in > Post Office co-axes using an HF carrier system, with a combination of > rebroadcast and microwave radio links for the more remote stations.] > > Hue error correction is just one component of the reason the PAL > pictures looked so much better than NTSC in the early days. There > *were* different production values: European lighting and set > designers avoided the gaudy sets used in US studio productions to > 'show off' color TV, instead letting natural color prevail (alas > those values have largely been lost!) The 576 active lines (versus > 480) plus the increased video bandwidth (by about the same ratio) > helped a lot. In PAL-I countries at least, the bandwidth could be > better exploited, as there was space for HF luminance components > above the 4.43MHz CSC notch, before cut-off at about 5.5MHz and the > receiver's 6MHz sound (aural) notch; things were much tighter between > 3.58 and 4.2MHz in NTSC land. And of course for PAL the distribution > was shorter: rather than syndicates 'out west', BBC TV's furthest > outpost was Shetland, a mere 600 miles from London. > > I don't feel the black level/blanking level difference was > noticeable. IIRC it was designed to minimise the visibility of sync > pulse overshoots during the line flyback (horizontal retrace) period, > but with improved blanking (suppression) in color TVs it became > unnecessary. In any case it was accepted practice even in PAL studios > to apply a set-up ('lift') of between 2 and 5% to the picture, which > amounted to much the same thing. The reduction of video dynamic range > (an SNR delta of <1dB) due to the IRE blanking level was surely > insignificant in analog days. > > 405-line pictures of course looked sharp because there *was* no CSC. > But still it needed good STLs, careful transmitter alignment and a > good TV to realise the system's potential 3MHz video bandwidth -- > most of the time you'd be lucky to see 2.5MHz in the home. 377 active > lines was only three-quarters of what US viewers were accustomed to, > and it showed. Don't forget also that sync separators were more art > than science in the pre-color days: TV sets frequently lost interlace > totally, giving the effect of seeing the world through a stationary > 188-line raster! And let's not forget the 10.125kHz line whistle and > the 50Hz field flicker on those fast-phosphor B&W tubes. That > delegation must have been used to some pretty rough 525-line stuff! > > SJB > > > > ---------------------------------------------------------------------- > You can UNSUBSCRIBE from the OpenDTV list in two ways: > > - Using the UNSUBSCRIBE command in your user configuration > settings at FreeLists.org > > - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the > word unsubscribe in the subject line. > > ---------------------------------------------------------------------- You can UNSUBSCRIBE from the OpenDTV list in two ways: - Using the UNSUBSCRIBE command in your user configuration settings at FreeLists.org - By sending a message to: opendtv-request@xxxxxxxxxxxxx with the word unsubscribe in the subject line.