The 4:2:0 is a standard format, derived from CCIR-601 (1982).
To quote Benoit (ch2 Digitization of Video Signals):
For applications that are less demanding in terms of resolution,
and in view of the bit-rate reduction, a certain number of by-products
of the 4:2:2 standard have been defined as follows:
The 4:2:0 format
This format is obtained from the 4:2:2 format by using the same
chroma samples for two successive lines, in order to reduce the
amount of memory required in processing circuitry while at the
same time giving a vertical resolution of the same order as the
horizontal resolution. Luminance and horizontal chrominance
resolutions are the same as for the 4:2:2 format
[...snip...]
In order to avoid the chrominance line flickering observed in
SECAM at sharp horizontal transients ... Cb and Cr samples are
obtained by interpolating 4:2:2 samples of the two successive
lines they will "colourize" at display time.
This 4:2:0 format is of special importance as it is the input
format used for D2-MAC and MPEG-2 (MP@ML) coding.
from Benoit, H.
Digital Television: MPEG-1, MPEG-2 and Principles
of the DVB System.
Arnold 1997
ISBN 0 340 69190 5
I recommend this book.itu.int/itudoc/itu-r/rec/index.html
http://www.amazon.co.uk/exec/obidos/ASIN/0340691905/o/qid=992447125/sr=8-4/202-9394619-8581457
Oh, in searching Amazon to get the above reference for you I found
that of the two customer reviews the second (5*) is also from a Philips
employee. This is clearly the book we crib all our stuff from ;-)
I've tried but failed to find the ITU specification itself online (not least
because their website seems to hate Mozilla - but that's a different
problem). There's a useful summary (with a link to the 4:2:0 variation)
at http://www.electric-words.com/dict/9/601ccir.html
Chris R.
On Tuesday 12 June 2001 23:12, you wrote:
> On 11-Jun-01 Gerd Knorr wrote:
> >> If V4L/V4L2 is going to include the Phillips packed 4:2:0 format, then
> >> it'd probably be best to call it PHILLIPS_420 or something like that,
> >> since there are obviously very many possible 4:2:0 packed format
> >> component orderings.
> >
> > Exactly that's why I'd like to know whenever the format used by the
> > phillips webcam is a standard format or some dirty hack by phillips
> > to make the hardware cheap: 420 instead of 422 to get more frames/sec
> > over usb and packed instead of planar because it's easier to handle.
>
> Well, since I am the author of this Philips driver[1], I can probably shed
> some light on this... The format produced _now_ by the driver is this:
>
> even lines: YYYY UU YYYY UU YYYY ...
> odd lines: YYYY VV YYYY VV YYYY ...
>
> (NB: this was clearly documented in the convertor routines). If this is
> standard or not, I don4t know.
>
> This is what comes out of the camera over the USB bus when in
> non-compressed mode. Since there was no definition given of YUV420, I
> choose that as the format for this palette. This is also the output of the
> decompressor routines (though it can also deliver YUV420P without penalty).
> Since there was also a definition of YUV420P, I added that with a simple
> convertor routine (it4s not really a convertor, just shuffling around bytes
> to the correct place).
>
> > I don't like the idea of adding non-standard formats to v4l/v4l2 ...
>
> That4s why I added a bunch of convertors, and this is exactly why I got so
> pissed off when Alan ripped out that code. The driver is now appearantly
> even less than brain-dead, since not a single tool, apart from my own
> camstream, can now use this driver. It delivers a format nobody
> understands, and the format it could use isn4t allowed.
>
> But, if nobody else uses this format, we might as well promote it to
> 4YUV4204 or ditch it all together. But in that case I must include code to
> go from internal format to YUV420P.
>itu.int/itudoc/itu-r/rec/index.html
> Oh yes, something else: it seems YUYV == YUV422 as well.
>
> - Nemosoft
>
> [1] One 4l4 only!
>
> ---------------------------------------------------------------------------
>-- Try SorceryNet! One of the best IRC-networks around!
> irc.sorcery.net:9000 URL: never IRC: nemosoft IscaBBS
> (bbs.isca.uiowa.edu): Nemosoft
>
> >> Never mind the daylight <<
>
> _______________________________________________
> Video4linux-list mailing list
> [EMAIL PROTECTED]
> https://listman.redhat.com/mailman/listinfo/video4linux-list
_______________________________________________
Video4linux-list mailing list
[EMAIL PROTECTED]
https://listman.redhat.com/mailman/listinfo/video4linux-list
