[opendtv] Re: HD vs. 625 vs. 525 vs. 405

I would like to share a few thoughts on quality perception of broadcast 
television.

The 405 system (System A) produced subjectively sharper pictures due to a 
number of factors. The original transmissions from London (until 1956) were 
double sideband (instead of vestigial sideband for all other systems 
since). This would lead to somewhat better video phase response due to the 
presence of both sidebands. Also, the Kell factor was 1.0 instead of 0.6 
for 525 systems. This lead to better horizontal resolution. I was impressed 
with off-air 405 years ago: the pictures looked good to the critical eye.

The move to vestigial sideband and Kell factor of 0.6 were motivated by the 
need to reduce transmission bandwidth. Like interlaced scanning and 
interleaved analog quadrature modulated chrominance systems (NTSC and PAL 
color), the analog bandwidth reduction methods were crude but of great 
benefit in the days before digital television signal processing became 
available. I constantly find amusement in the fact that we in the TV 
business still rely on these bygone methods and technology.

I mentioned earlier that the BBC no longer accepts PAL format tapes for 
transmission.  The move is slow in the US to abandon NTSC production and 
delivery and I feel this is slowing down the DTV transition in this 
country.  Broadcasters and service providers are going to have to go the 
extra mile to ensure that production and delivery is cleaned up.

Also, the public perception of HDTV is curious after experiencing the 
following incident. I was in a large major television showroom only last 
weekend and was pleasantly surprised to see an 'Olympics DTV' display. 
However, upon closer investigation, I discovered the 61" Wega display 
costing retail $19,000 was displaying the HD Olympics from our local NBC 
affiliate off-the-air with noticeable NTSC chroma crawl. I questioned the 
Sales Manager. He insisted it was HD....he pointed to a DTV set top box and 
to the big display.

I pointed out to him that the display was connected via the composite NTSC 
interface: I helped him set it set up and the difference was dramatic. It 
was like this for a week with the NTSC interface and why nobody noticed 
escapes me.

Bravo to Sinclair for taking the lead as a broadcaster promoting over the 
air DTV.  However, more consumer education is definitely required.

Regards,

Terry Harvey
------------------------------------------------------------------------------

At 06:32 PM 8/27/2004 -0400, Mark Schubin wrote:
>Having just returned from a shoot in New Zealand, I thought I'd throw my
>two cents in on this.
>
>Back in the early 1950s, a U.S. delegation toured UK TV facilities to
>try to determine why UK pictures looked better.  At the time, the UK was
>405 lines, not 625, but it was still said to have better pictures.  The
>delegation determined it was because the UK equipment was better
>maintained -- clean lenses, etc.
>
>I found the same in New Zealand.  The equipment was in impeccable shape.
>
>Food for thought:
>
>- The resolution of human vision tops out at about 30 cycles per degree,
>nominally about 22.
>
>- U.S. viewers sit about 9 feet from their TV sets (the Lechner distance).
>
>- Those two facts combine to make it impossible for viewers to see more
>than 480 lines on a 25-inch 4:3 TV at normal viewing distance.  If it's
>22 cpd and 16:9, it's no more than 480 lines on a 42-inch set.
>
>- Meanwhile, because the psychological sensation of "sharpness" is
>proportional to the square of the area under an MTF curve and the use of
>HD in production leads to a higher MTF curve at all detail resolutions,
>a viewer watching a non-HD set will nevertheless see an improvement in
>sharpness from HD-shot programming.
>
>TTFN,
>Mark
>
>
>
>
>
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