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

Eh? My CRT TV switches both. It switches between 16:9 and 4:3 - by
altering the horizontal scan width. It switches also for PAL/NTSC. No
idea where you got the idea that CRT TV "never had" this after 405
line. Not all do, I guess, but I doubt my set is unique!

The widescreen sets that I have experience of switch between 16:9 and
4:3 by time-compressing 4:3 video in the digital process area rather
than altering the scan width.

Erm...

For CRT that would make little sense to me. Perhaps you aren't making it
clear, or are confusing different things. Are you saying every 16:9 CRT
you've used displays 4:3 by scanning the entire 16:9 area, but puts the 4:3
image into the central portion? if so, why does it do this when fed with
something like 4:3 via SCART? Seems a weird option to me. Changing
the amplitude of the horizontal scan level seems a trivially easier
way to deal with the matter, and probably gives better results.

Mind you, I never cease to be impressed by the mindless ways some TV
manufacturers invent 'around the barn' ways to make things needlessly
complex so as to sell the result as being 'clever'. Bolony still
baffles brains, I guess, even after all these years... :-)

But so far as I can tell, when my TV CRT sees the input change to 4:3
from 16:9 there is a click as the horizontal scan amplitude alters, and the
picture falls back into the central portion of the screen. No scanning
outwith that area. Since it is a pretty standard Panasonic CRT set bought
just a few years ago I assume this is a fairly standard option. Seems like
sensible engineering to me. But if what you say is right Panasonic seem to
have shown rather more sense than other makers. Are they unique? I'd
be surprised to find they were given the simplicity of the method.

I'd agree that the levels used for the scans are set 'digitally', though,
as the widths, etc, are all accessible via onscreen menus - once you have
found the hidden service menus. :-) I assume this just means the scaling
voltages are held in something like a non-volatile RAM and then used to
reference the sizes of the analogue scan waveforms. But perhaps they do
write waveforms into RAM to get shapes right, then read the RAM series
during each line and frame. Not exactly what I'd call 'digital processing',
though. Just like using look up tables with a cheap sig gen.


Once the digital box is present it's cheaper to do it that way. But if
your set does it by altering the scan width then clearly not *all* do it
digitally.

Depends what you mean. See above. You may be confusing a 'digital box'
(i.e. external tuner) having to do the job with the display coping
with changes in aspect.


OK, I'll rephase my remark as "Since the end of 405-line
transmissions 4:3 TV sets (as opposed to computer monitors) have never
had switching for horizontal scan frequency or width".

Your point being that sets made with no provision for other than 4:3
have no provision for other than 4:3? I can see the logic of that. ;-

Slainte,

Jim

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