Wide screen TV woes

One just wonders then, why did TV reinvent the wheel and go for a close but
not the same aspect ratio in the first place?

Brian

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Brian Gaff....Note, this account does not accept Bcc: email.
graphics are great, but the blind can't hear them
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"Andy Burns" wrote in message
...
On 09/12/2007 22:36, Bart C wrote:

The image could have been scaled vertically to use 576 lines then
adjusted on the TV.

Would you have preferred it to be stretched vertically leaving everything
tall and thin, or stretched in both directions and then have the edges cut
off?

Not all DVDs (barely any films on DVD) are 16:9, they tend to stick close
to the cinema ratios.

"Martin Jay" wrote in message
...
On 09/12/2007 22:36, Bart C wrote:

Most of my movies are 4:3 B&W, haven't tried those yet.

Oh dear. I have a feeling you'll be disappointed with the black bars
down the left and right hand side of the picture.

I saw one last night (in technicolour though). Strangely those bars aren't
as annoying. I'm looking at presumably the full 576x720 information from the
DVD, and the picture is just as tall, maybe 1-2cm more (on this 26" set) as
on my previous 21" CRT. So it doesn't seem like I'm missing out on anything.

It seemed to me that changing to wide screen often meant losing vertical
height on your existing TV (bad) instead of gaining width compared to your
existing TV (good). But most people didn't seem bothered.

Bart

"kim" wrote in message
...

No they can't. DVD is restricted to a maximum of 720 horizontal pixels so
whichever way they're pulled off the disc you're going to lose picture
resolution. To do as you suggest would require a DVD with around a 1,000
horizontal pixels, a third of these being wasted in zoom mode.

Everybody is talking about 720 horizontal pixels but when I did the maths it
seemed to need 768 pixels for 4:3 aspect, when the pixels are square. 720
gives you 5:4 aspect on square pixels. So SDTV pixels are not square
especially stretched for wide-screen. Wide-screen 16:9 would need 1024x576
for square pixels, which strangely is what you've said.

(I used to build frame grabbers many years ago so have a bit of a
preoccupation with the figures)

"Bart C" wrote in message
. uk...

"kim" wrote in message
...
Bart C wrote:
"Andy Burns" wrote in message
...
On 09/12/2007 22:36, Bart C wrote:

I like the picture to fill the screen vertically, no wasted blank
areas. And no distortion (so people look neither tall nor fat). That
would mean losing left and right portions of cinemascope-type movies
(they can still be on the DVD but scaled off the TV when viewed this
way).

No they can't. DVD is restricted to a maximum of 720 horizontal pixels so
whichever way they're pulled off the disc you're going to lose picture
resolution. To do as you suggest would require a DVD with around a 1,000
horizontal pixels, a third of these being wasted in zoom mode.

This is a murky area for me. So wide screen on DVD is achieved by
squeezing the horizontal into the same 720 pixels as used for 4:3?

Then yes a lot of picture detail would be lost when scaling a cinemascope
picture equally to fill the screen vertically: the sides chopped off and
the visible pixels stretched horizontally.

The solution then, for movies to be viewed in 16:9, would be to pan&scan
them into 16:9 and to fill the frame. Then all the available resolution
would be utilised. That would suit me.

I know exactly what you mean. Isn't it annoying to have a nice TV only to
find bits chopped off the picture. Wouldn't you think that the TV could
"fit" the picture to the screen size correctly. If I watch a 14" portable I
don't just get the middle square of a picture I would see when I watched a
28".
Why can't I get a DVD that will fill the screen. Why are TVs made to a
certain screen size if the manufacturers know no one can use them fully.

On 10/12/2007 12:59, John wrote:

I know exactly what you mean. Isn't it annoying to have a nice TV only to
find bits chopped off the picture. Wouldn't you think that the TV could
"fit" the picture to the screen size correctly.

most TV's can alter the aspect ratio, to zoom/stretch/crop pictures to
suit, yes you lose resolution and/or sections of the picture by doing
do, and it you do it badly (like Joe Public) you get stretched pictures
too boot.

What alternative do you suggest?

On 10 Dec, 00:55, "Bart C" wrote:

The solution then, for movies to be viewed in 16:9, would be to pan&scan
them into 16:9 and to fill the frame. Then all the available resolution
would be utilised. That would suit me.

You will enjoy broadcasts of greater-than-16:9 films on TV then - they
often to this.

I think it looks horrible - even worse than 2.35:1 pan-and-scan to 4:3
- you might lose less going to 16:9, but it's harder to make something
that looks "nice" in its own right.

Cheers,
David.

"Bart C" wrote in message
k...

"kim" wrote in message
...

No they can't. DVD is restricted to a maximum of 720 horizontal pixels so
whichever way they're pulled off the disc you're going to lose picture
resolution. To do as you suggest would require a DVD with around a 1,000
horizontal pixels, a third of these being wasted in zoom mode.

Everybody is talking about 720 horizontal pixels but when I did the maths
it seemed to need 768 pixels for 4:3 aspect, when the pixels are square.
720 gives you 5:4 aspect on square pixels. So SDTV pixels are not square
especially stretched for wide-screen. Wide-screen 16:9 would need 1024x576
for square pixels, which strangely is what you've said.

(I used to build frame grabbers many years ago so have a bit of a
preoccupation with the figures)




not all the image is visible - some of it is offscreen - used for teletext
in broadcast for example.


--
Gareth.

That fly... is your magic wand.
http://www.last.fm/user/dsbmusic/

Bart C wrote:
"kim" wrote in message
...

No they can't. DVD is restricted to a maximum of 720 horizontal
pixels so whichever way they're pulled off the disc you're going to
lose picture resolution. To do as you suggest would require a DVD
with around a 1,000 horizontal pixels, a third of these being wasted
in zoom mode.

Everybody is talking about 720 horizontal pixels but when I did the
maths it seemed to need 768 pixels for 4:3 aspect, when the pixels
are square. 720 gives you 5:4 aspect on square pixels. So SDTV pixels
are not square especially stretched for wide-screen.

Correct. The pixel shape was compromised for a resolution of somewhere
between 4:3 and 16:9. They could easily have opted for 1024 pixels for
widescreen movies but for some reason chose not to. You have to remember
that when the DVD spec was first drawn up hardly anyone owned a 16:9 screen.

(kim)

Brian Gaff wrote:
One just wonders then, why did TV reinvent the wheel and go for a
close but not the same aspect ratio in the first place?

The same aspect ratio as what? Early movies weren't widescreen.

(kim)

kim wrote:

Everybody is talking about 720 horizontal pixels but when I did the
maths it seemed to need 768 pixels for 4:3 aspect, when the pixels
are square. 720 gives you 5:4 aspect on square pixels. So SDTV pixels
are not square especially stretched for wide-screen.

Correct. The pixel shape was compromised for a resolution of somewhere
between 4:3 and 16:9. They could easily have opted for 1024 pixels for
widescreen movies but for some reason chose not to. You have to
remember that when the DVD spec was first drawn up hardly anyone
owned a 16:9 screen.

All digital (SD resolution) consumer video formats - VCD, DVD, SVCD, DV,
DVB, etc. - are, in one way or the other, based on a standard called
ITU-R BT.601. (Or "CCIR 601", by its old name.)

This standard defines that analogue video be sampled at a 13.5 MHz
sampling rate.

Since each scanline lasts 64 µs, this sampling rate yields 864 pixels
per scanline (13.5 MHz * 64 µs = 864). Not all of that information is
needed, however, since a significant part of each scanline is used for
horizontal blanking and the synchronization signals and colour burst
that occur during that time.

Since the "active" part of each 64 µs scanline (i.e., the part
containing picture) only lasts for 52 µs, the rest (that is, the
horizontal blanking - 12 µs) can be ignored.

52 µs * 13.5 MHz = 702 pixels, but in reality, ITU-R BT.601 mandates
that 53.333... µs (720 pixels) be sampled.

The 9 extra pixels on the sides are padding whose purpose is best
explained in these two old messages:

http://google.com/groups?selm=01c131...%24712b7c0a%40
pc-l301385.wn.bbc.co.uk

http://google.com/groups?selm=01be9b...%24652b7c0a%40
pc-234866.wn.bbc.co.uk

Originally - when video and tv cameras still were analogue - those 9
extra pixels on the sides would only have contained black. These days,
however, many video cameras record full digital picture all the way to
the edges. (Some still don't, though, and there's black on the edges.)

The tricky thing in all this is that the correct picture geometry is
always calculated based on the original analogue video definition: 52 µs
(702 pixels at a 13.5 MHz sampling date) and not from the full width of
720 pixels in digital video formats.

If you need square-pixel equivalents of the common digital video
resolutions and aspect ratios, they would go as follows:

For full-frame 16:9 625/50 format with ITU-R BT.601 13.5 MHz pixels, the
pixel aspect ratio is 512/351 (x/y):

720×576 DVD/DV pixels in 16F16 mode =~ 1050×576 square pixels
704×576 DVD/DV pixels in 16F16 mode =~ 1027×576 square pixels
702×576 DVD/DV pixels in 16F16 mode == 1024×576 square pixels

For full-frame 4:3 625/50 format with ITU-R BT.601 13.5 MHz pixels, the
pixel aspect ratio is 128/117 (x/y):

720×576 DVD/DV pixels in 12F12 mode =~ 788×576 square pixels
704×576 DVD/DV pixels in 12F12 mode =~ 770×576 square pixels
702×576 DVD/DV pixels in 12F12 mode == 768×576 square pixels

--
znark