Newsgroup: it.media.video.produzione
Titolo: 4:2:2, 4:1:1, 4:2:0

Ho trovato in rete una interessante spiegazione della differenza fra
4:2:2, 4:1:1, 4:2:0 che vi giro integralmente
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  These are all shorthand notations for different sampling structures for
digital video. They are also used for CIF and QSIF and suchlike MPEG frame
sizes, but in the discussion that follows, I focus on the numbers for SDTV
(standard-definition TV) digitized to the ITU-R BT.601 standards: 13.5 MHz
sample frequency and 720 pixels per line.
  The first number refers to the 13.5 MHz sampling rate of the luma: "4"
because (a) it's nominally almost approximately sort of four times the NTSC
and/or PAL color subcarrier frequencies, and (b) because if it's "4" the
other numbers can be integers whereas if it were "1" the formats would be
"1:0.5:0.5", "1:0.25:0.25", and "1:0.5:0" respectively, and which would you
rather try to read off in a hurry? The 13.5 MHz sampling yields 720 pixels
per scanline in both 525/59.94 and 625/50 systems (NTSC and PAL/SECAM). This
number applies to D-1, D-5, Digital Betacam, BetaSX, Digital-S, and all the
DV formats just the same.
  The other two numbers refer to the sampling rates of the color difference
signals R-Y and B-Y (or, more properly in the digital domain, Cr and Cb)
  In 4:2:2 systems (D-1, D-5, DigiBeta, BetaSX, Digital-S, DVCPRO50) the
color is sampled at half the rate of the luma, with both color-difference
samples co-sited (located at the same place) as the alternate luma samples.
Thus you have 360 color samples (in each of Cr and Cb) per scanline.
  In 4:1:1 systems (NTSC DV & DVCAM, DVCPRO) the color data are sampled half
as frequently as in 4:2:2, resulting in 180 color samples per scanline. The
Cr and Cb samples are considered to be co-sited with every fourth luma
sample. Yes, this sounds horrible -- but it's still enough for a color
bandwidth extending to around 1.5 MHz, about the same color bandwidth as
Betacam SP (which, were it a digital format, would be characterized as
3:1:1).
  So where does 4:2:0 (PAL DV, DVD, main-profile MPEG-2) fit in? 4 x Y, 2 x
Cr, and 0 x Cb? Fortunately not! 4:2:0 is the non-intuitive notation for
half-luma-rate sampling of color in both the horizontal and vertical
dimensions. Chroma is sampled 360 times per line, but only on every other
line of each field. The theory here is that by evenly subsampling chroma in
both H and V dimensions, you get a better image than the seemingly
unbalanced 4:1:1, where the vertical color resolution appears to be four
times the horizontal color resolution. Alas, it ain't so: while 4:2:0 works
well with PAL and SECAM color encoding and broadcasting, interlace already
diminishes vertical resolution, and the heavy filtering needed to properly
process 4:2:0 images causes noticeable losses; as a result, multigeneration
work in 4:2:0 is much more subject to visible degradation than
multigeneration work in 4:1:1.


....................
...questa qui è una cazzata ! Infatti a sua discolpa dice "if where it a
digital
format" (il che non è...). La larghezza di banda del croma del beta
è piena (4,2 MHz) , solo eterodinata line by line U e V.

 č piena (4,2 MHz) , solo eterodinata line by line U e V.
si. č un esempio infelice