pixel AR (for ambitious reader) intended, content, about, wrong

andy

this spun-off is a reaction to
discussions here:
showthread.php?s=amp;threadid=50438
(dig in,you'll find it; myself and wilbert took
part)
firstly intended to be PM (to wilbert of avs team),it's here now for anyone
that wants to get a bit deeper....PM subject;quot;just that a basics are wrong (hehe)quot;

PM content;
quot;
i see you have few misconceptions,let's see:

gt;We are not talking about 59/54 mpeg2 pixel, but we are talking about PAL 59/54 pixel.

59/54 pixel IS PAL MPEG2 PIXEL ONLY!!!
59/54 IS NOT OVERALL quotALquot; pixel!!!
pal pixel is the pixel i choose with
resolution/quot;h-scalequot; setting of bt8x8 tweaker
(users on non bt8x8 devices only rely on driver/
manufacturer that they respected 59/54 pixel
for 720x576 res.....
704x576 is offcourse NOT 59/54 )
[don't mind this shouting,i'm just
underlining some facts]
ok?
on 768x576 this pixels becomes perfectly square
on bt8x8 device...this is clearly stated even
in bt8x8 datasheet.....
(nice read for hardware enthusiasts...there was a link
recently to complete conexant pdf chips library)
{edit:here
showthread.ph...ight=datasheet
or only
products/tec...tail.jsp?id=10 }
my pixel can be anything i choose it to be (off course
within the limits of the hardware)

in different words;mpeg2 59/54 pixel is same one as
PAL captured on 720x576 to .avi (if manufacturer respected ccir601)
BUT PAL captured on 768x576 is 1:1 pixel!

gt;But your broadcasting station is broadcasting 720x576 frames, and not in 4:3

this is big misconception and probably root for all
others:listen ;
analog videosignal is not measured in pixels at all!
it's measured in the precision of line drawing on the screen
(VHS is not so precise,broadcast PAL is much better)
this quot;videosignal precisionquot;(or quality of the line precision)
is measured by quot;bandwidthquot; in MHz for analog signals
(vhs peaks at cca. 3MHZ,broadcast PAL should be cca.4
theoretical limit is 5,5MHz but is never achieved in field)
so ..my broadcast station is transmitting bandwidth of PAL signal,not pixels
(i'm talking about analog PAL transmission over the satellitte
or terrestrial)

gt; If it isn't, those extra 17+5/59 pixels must be black, or the image on your television itself is slightly stretched

another basic;tv projects images ALWAYS a bit over stretched
(so called quot;overscanquot;)
720x576 of mpeg2 still has some image parts you don't see on dvd-player+tv..(quot;Note that a 720 pixel scanline has thus captured an extra 17+5/59 pixels! quot;).but you clearly see them on monitor!
(remember...monitor and PC project only square pixels...so you'll
not fill monitor with 720x576 mpeg2 but will fill tvscreen with dvd player and 720x576 mpeg2)

back to the subject;
analog PAL is NOT 720x576,but it's true that it has 576 quot;scanlinesquot;...
(so this is reference for us)
576x1,3333 (tv indeed had 4:3 AR)=gt;768...
768x576 is perfect for PAL capturing......
(i would like some more than 768,but...then it wouldn't be square pixel,would it...
hehe)

(almost) special case of DVB;
DVB is indeed 720x576,but you will prefer to capture it
to 768x576 too if you aim for mpeg4 video (square pixel)
as one can view this 720x576 as a NORMAL PAL LINE with
correct AR (video signal has no distinction of
pixelAR or so...)
if you aim for mpeg2 you prefer 720x576...so you have
correct pixelAR to make dvd!
(so DVB can be viewed as normal analog PAL all the way...by the time it gets to your capture card it is that;normal analog PAL video signal)

final note;720x576 and 768x576 contain same line width (so to speak),
same image information
only i would prefer 768 line as it has more pixels!
(let alone that 720 pixel is 59/54....more is always more..more resolution is more resolution...you might see that
mjpeg on 720x576 has slightly more mosquito noise than
768x576....)
one might say that 768 has more detail than 720 pixels...
pixel is the smallest unit and has discrete value to it ,ergo
768 has more pixels and more info than 720 (no matter the pixelAR...
still one pixel has only ONE part,ONE portion of complete image,
within that ONE pixel there's no deeper detail...,blow image real hard
to see it---gt; one pixel has only ONE shade of gray
OR one color within it...)

hope this helps
(huh this is so good i might make a thread out of it...
for freaks only...hehe)
quot;oups a mild headache after all this writing and uploading...
i'll rest now....

regards
/ivo

Good links for this whole AR/PAR issue:

From programmers.html :

znark/video/
(many good stuff, newsgroup links, Jukka's explanations etc. )

From  :

derkarl/index.html
(german only, will be maybe translated to english soon)

From this board:showthread.php?s=amp;threadid=42708

etc.

Make some more forum searchs, read Doom9's guides (Doom9, BTW, doesn't uses the ITU recommandations, IIRC)...