What can a PAL-TV actually display??

[Atax]

Hi all,

the video-material on a PAL-DVD is stored in 720 x 576 pixels, but can a PAL-TV even display this resolution?

A PAL-TV-Pictures is bild up by 625 vertical lines, so there should be no trouble displaying the 576 pixels making up the vertikal resolution, right? But how is it with the horizontal resolution??, ... any idea how it is with that?

Thanks in advance

Atax

[hakko504]

Almost all TV:s have a resolution good enough to find the individual pixels from the 720x576 DVD - if it is transferred properly from the DVD player to the TV, i.e. using RGB. Start mucking with S-video or CVBS and you'll loose resolution in the transfer. S-video will not loose very much though, maybe just a few % where CVBS will visibly degrade the quality of the picture. Small TV:s (and some larger ones too) will cheat though by cropping the picture, sometimes by as much as 10% on each side, leaving only 576x460 as the active viewing area. Many newer TV:s of a cheaper kind use this trick to gain compatibilty with NTSC!

[ultimatebilly]

The PAL-standard is described in the ITU-R BT.601-5, if you really want to know the details, you should get the document, if I remember correctly, you can get 3 documents for free from the ITU-Homepage...
Back to PAL:
If you divide one second by 25 frames, then you get the duration of a PAL frame, 40 milliseconds.
If you divide this by 625 lines, then you get 64 microseconds.
Thus a single PAL-line has a duration of 64 microseconds.

The sampling frequency of the luminance-information is 13.5 MHz, that means the information in the luminance-part of the video is sampled 13.5 million times in a second.
If you multiply the sampling rate by the duration of a single line, you get 864 samples per line...

13500000 Hz*0.000064 s = 864 samples.

Note that this is only brutto, because there is much of line synchronization, blanking information and field synchronisation in it...
The active picture area is according to the ITU only 52 microseconds long...
The ITU says also that a line has 720 active samples, the rest is blanking information (do they still say so? I'm not up to date).

If you divide the duration of a single line by the samples in it, you get the length of one sample:

64/864=74.074ns

Multiplied by the value of samples the ITU regards as active, you get a "active line duration" of 53.3333microseconds:

74.074ns*720=53.3333 microseconds.

But according to all sources, the duration of the active part of a line is 52 microseconds (the ITU is contradicting itself here).
If you calculate with that value, you get a different result:

52 microseconds/74.074ns=702.0007 - 702 pixel per line.

Thus the active duration of a line is 702 pixel plus 9 pixel overscan per side, 720 pixel total.
You see now, that there is no difference between the resolutions 704x576 and 720x576, because they contain exactly the same motion area...

But that's not all...
The standard aspect ratio for PAL is 4:3...
But 576*4:3 is 768...
How does this fit into the ITU-recommendation of 702 pixels active line duration?
This is because TVs have, contrary to PC-monitors, a pixel aspect ratio, which is 59/54, the pixels are more broader than high...
That means that every pixel is not square, but rectangle.
If you divide 768 by 59/54, you get 702,92 pixel, which is almost the active picture duration according to the ITU...

So, coming back to your question:
The PAL-TV-Standard has a horizontal resolution of 702 pixels...

I have to admit at this point that it's not me that is so smart, I have blatantly copied all calculations in this thread from the wonderful guide "Capture-Karten und aspect-ratio für Dummies ;-)", written by Der Karl, presupposing his permission.
Find the original (in german) here: Videoxone (http://www.videoxone.de/cgi-bin/load.pl?page=derkarl)

Additional information about correct resizing can be found here:

http://www.mir.com/DMG/aspect.html

and here:

http://www.iki.fi/znark/video/conversion/

If you're wondering why there is an "Follow the ITU"-option in GordianKnot which gives you an aspect ratio in relation to 788x576, this is because many many people in the world of video obviously don't understand this whole mess correctly and use therefore the whole 720x576 resolution of the DVD, and not only 702 (or 704)...
If you multiply this by 59/54, then you get 788 (well, something near enough)...
So, if you have a DVD with 720 pixel active picture information, and you believe that the composers of the DVD were smart enough to process the data in a way that it is shown correctly on the TV, then you should use this option and resize to something compliant to 788x576, otherwise you will get (very) slight eggheads...
There are many people who don't believe in the ITU-Recommendation, but I do as you can see :D

Another note:
I really prefer 704 over 720 for another reason:
704 has not only less overscan, it is in addition to that divisible by 32...
What's so great about that?
Well, since all MPEG-formats rely on macroblocks which use 4 8x8 blocks, in whole 16x16, you achieve of course better compressibility when using resolutions divisible by 16, but even better compressibility when the resolution is divisible by 32... Why so? Because there is a better chance that the macroblocks will find a match in the previous or following frame when there is an equal amount of them, not an odd one...
And even when one is letterboxing to 720, then the additional 2 half horizontal macroblocks are better then 2 half macroblocks of active picture (which can't be seen on TV anyways).
But then you have two columns of macroblocks which are more unlikely to match, because they can only match above or below them, not right or left of them (well, if there is one macroblock that is exactly the same, with the half of it black, then it's a different thing of course)...
With XviD, the mod32-resolution is not that mandatory, because the codec can store 4 vectors per macroblock (and XviD is great, anyway :D )

[magnetoskop]

ultimatebilly,guy just asked how much of res. can pal-tv display,and you teached us all about...hmmm,what precisely?

in fact,horizontal resolution question is pretty interesting,for further reading see this (http://forum.doom9.org/showthread.php?s=&threadid=34122&highlight=pal+resolution+is+AND+vhs+resolution+is) link........

to condense that knowledge it all comes down to this:while vertical number of scanlines is the number you mentioned,the h.res varies with the bandwidth of the signal itself:vhs has lower bandwidth than broadcast signal,and therefore will transmit less detailed image....
the highest res of analog system is the number of vertical lines (for example alternate b/w trees or so..) that can be diferenttiated on the screen.........

the usual numbers say that vhs is cca.240 lines of this (h) resolution(or cca. 3MHz bandwidtht),and normal broadcast tv probably lies at the cca. 4MHz or 320 lines of h.resolution.......
if you have a video source capable of 5Mhz and tv capable of reproducing this,then consider yourself lucky
(i guess you can get some dvd test discs that would show you what's your gear capable of.....)
i believe that dvd video signal (after d/a conversion in dvd player) won't give you 5MHz(5x80=400 lines) figure for a number of reasons (one obviously being the lossy nature of the codec...)
(5MHz is absolutte theoretical roof which you cannot brake on consumer pal-tv....it's usually more like mentioned 4MHz that draws the lines on your screen....)

the dvd test disc i'm talking about should have same test paterns as the ones you might see sometimes before the end of tv transmission for that day....those vertical lines etc.

also,after the mpeg2 signal is converted to analog,there are no "pixels" in that sense......only the continuous pal lines (ie. pixels from one line become pure analog tv-line as any other analog line we feed the tv with (vhs,ananlog pal etc.)

and so,4MHz (320 lines) is usual,5MHz(400 lines) is excellent but hard to achieve in reality........

[ultimatebilly]

hmmm,what precisely?
Good question! :D
Maybe the maximal horizontal resolution which is possible in PAL? Well, at least in studio signals...

5MHz is absolutte theoretical roof which you cannot brake on consumer pal-tv....it's usually more like mentioned 4MHz that draws the lines on your screen...

I didn't know that...
But that would mean that there would be no real difference between SVCD and DVD resolution on a normal PAL-TV?!

Have to read more about this...