Dumb question...

[~Yuckfou~]

I'm having a "blonde" moment

What resolution is TV?

I ask because I'm burning some home video to dvd and trying to keep the file sizes as small as possible, while maintaining image quality.

Ta muchly.

 

[Tom]

PAL = 768 x 576, 4:3

Anamorphic 16:9 is the same resolution

 

[~Yuckfou~]

Ta

 

[SheepCow]

DVDs are 720x576

 

[Tom]

Do DVDs use square pixels? Doesn't sound like it.

 

[SheepCow]

A 16:9 DVD is stored on the disk as a squashed 1024x576 image down to 720x576, the player/tv then stretches it back out to 1024x576 for correct viewing aspect ratio

 

[Tom]

Its just odd that they use 720 pixels. Does this figure include line sync pulses, or is the data stored without them, and the DVD player generates them when outputting to PAL?

The process 'squashed' is actually known as anamorphic (although your Grandma can already suck eggs I reckon), and is still used in cinema projectors today.

 

[mookie]

interesting topic, its something i've never really understood, seems like a good chance to sort it out?

from what i've just read, anamorphic 16:9 is just standard resolution 'stretched' and then put on the disc?.

just like when the parents put the tv in 16:9 mode and make everyone look chubby?

 

[Tom]

Thats exactly right.

In cinema, when you're making a film in widescreen, you run standard 35mm film through the camera, but the lens on the front of the camera anamorphically 'squashes' the image horizontally (this is optical, not electronic), so you can fit more picture information in each frame. If you turn the lens 90degrees, the angle of compression changes as well. The resolution of film is more than high enough to make this process pretty much invisible in terms of any loss in quality.

Its pretty much the same in video, but on television cameras, rather than have 3*4:3 chips, you have 3*16:9 chips, and no 'squashing' takes place, as broadcast mediums record the full 16:9 resolution without any squashing. Television lenses are not anamorphic.

When it comes to transmission over the air/cable/satellite, all stations transmit in 4:3, because they have to remain compliant with the PAL standard. The widescreen channels, even while broadcasting in 4:3, anamorphically squash the 16:9 image. When you watch it on your 16:9 TV, the TV stretches the 4:3 image back out to the correct dimensions. This results in a loss of horizontal resolution, but its not normally noticeable (although you will see a noticeable difference on monochrome broadcasts).

I was just wondering how the picture information is stored on a DVD. Does it store the full 16:9 resolution, and then convert it to a 4:3 anamorphically compressed image for your television? Or is the movie/video/whatever written to the DVD as anamorphically compressed 16:9?

 

[SheepCow]

They are stored in 16:9 anamorphic MPEG2 on the disc

 

[Tom]

So, basically a 4:3 image?

 

[old.user4556]

It depends on the disc/film doesn't it?

DVDs can have 4:3 or 16:9 iirc...

 

[SheepCow]

Nope, DVDs always have a 4:3 image stored on the DVD, the MPEG headers (I'm assuming) tell the DVD player to stretch it out to 16:9 or not.

 

[Tom]

I think something on the video data causes the DVD player to change the voltage on a pin at the SCART lead, and the TV detects that and auto-switches.

Its a bastard really, cos my Tivo isn't clever enough to do that for me

 

[old.user4556]

Nope, DVDs always have a 4:3 image stored on the DVD, the MPEG headers (I'm assuming) tell the DVD player to stretch it out to 16:9 or not.

Ah I see, we're both correct on this point depending on how you word it. I googled for it for a better explanation, and from the DVD faq i got this:

DVD is specially designed to support widescreen displays. Widescreen 16:9 video, such as from a 16:9 video camera, can be stored on the disc in anamorphic form, meaning the picture is squeezed horizontally to fit the standard 4:3 rectangle, then unsqueezed during playback.

So yes, it's in 16:9 but the picture is technically 4:3 or a 'squeezed 16:9 to fit a 4:3 TV' picture. By setting the DVD player to 4:3 in the setup, I expect it shows the 16:9 picture letterboxed in the 4:3 frame (it does on my projector anyway).

Personally i think 4:3 is the spawn of satan and needs binned. I see the US are decommisioning NTSC in 2006 in favour of 16:9 HDTV.

Tom, being a broadcast/TV blokey; where do you see UK broadcasting going in the next couple of years? Anything similar to HDTV?

G

 

[~Yuckfou~]

jeez, looks like I turned over a stone here

 

[mookie]

this is a really interesting document that just explained all my questions about dvds. well worth the read.

 

[smurkin]

Good Thread

 

[Tom]

Tom, being a broadcast/TV blokey; where do you see UK broadcasting going in the next couple of years? Anything similar to HDTV?

G

There was a big debate on an industry forum I use recently, regarding the selloff of frequencies later in this decade. The original plan was to give everybody access to digital television in one form or the other, and then 'switch off' the terrestrial analogue frequencies we currently use. It looks like that date is going to be pushed back, because the takeup has been slower than expected. This will happen, but the debate was over Channels 68 and 69, which currently house frequencies used to wireless radio mics. At £2000 a pop (I now have 3 of them), its a very significant sum to ask sound recordists to find in order to reinvest in newer equipment, not to mention all the systems owned by production companies, hire companies, etc. Looks like channel 69 is to be left alone for now

They will do it eventually, just like they turned off the old 405 line system (in the 80's?).

I personally don't believe HDTV will come anytime soon. Its not something that consumers seem to be interested in, and the costs involved for the broadcast industry, and the consumer, would be significant. Perhaps SKY would consider a HDTV movie channel, but it would be very expensive, SKY would have to charge quite a high price to recoup their costs on each transmission. In the US I think its more successful, but they have a much larger market.

For now, widescreen is the flavour of the month. I just wish that producers/directors would pay more attention to sound issues (thats mostly what I do these days, record audio), most of them are totally ignorant of what is required for good quality sound on programming. Everybody has stereo televisions, but whatever I shoot, nobody ever wants stereo recordings! Bloody annoying, especially when they overlay stereo music onto the footage!