In article , David Looser
wrote:
"Jim Lesurf" wrote in message
...

You presume also that the entire display area, and every pixel, *must*
be used at all times. :-)

No I'm not, quite the opposite.

OK. Then given a display with a number of pixels to match the highest
definition in use, you could choose to use a subset for low definitions,
and then no processing of the image data would be required.


...but with an analogue CRT none of the 'faffing about' causes any
addition delays for the displayed image. One of those cases where a
simple analogue method works quite neatly.

Only if that option exists.

....as is true for anything. I agree, though, that if you don't have CRT,
then you can't use it. :-) Doesn't make my point invalid, though.


DVD players and DVB boxes can optionally convert 16:9 material to either
"pan & scan" or letterboxed 4:3, This is a digital process. I do agree
that this is performed fast enough not to cause lip-sync problems, but
it is very definitely "faffing about".

....and you are referring to the source behaviour, not the display.

With a CRT in principle all you have to do is allow the CRT to switch scan
width. No need for any 'pan and scan' or 'letterbox' processing by either
source or display.

The letterbox option *can* be acheived simply by reducing the vertical
scan amplitude, but only a minority of 4:3 TV sets have that facility.

In such cases the image data isn't 'processed', so no 'faffing' about
of it is required. In principle, all that happens with CRT is some
analogue scan waveforms are altered, essentially just in amplitude.

When done by the TV, yes. When done in the DVD player or DVB box, no.

I had thought we had been discussing lip synch delays caused by *displays*.
For fairly obvious reasons, if a source like a DVD player or tuner has to
have a process delay for the image it can easily then apply a similar delay
to the sound. This just requires the designer to know what they are doing.
However when the display has a vision delay, the designer may have no
control over the sound path from an external source feeding video to the
display.

Slainte,

Jim

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