> I recently found and read the above document, which has helped to720 luminance pixels (digital active line) at 13.5MHz pixel-rate is a time
> confuse me more than I was before about 625-line TV/DVB broadcasting:
> The ITU BT.601 standard (digital TV) specifies a line length of 720
of 53.3 microseconds.
Analogue video from a 625/50 blanked camera Y output will be 52
microseconds in width between half-amplitude points,
so the analogue active-line period of a picture source is nominally 702
pixels. (702 x 1/13.5MHz = 52 micosecs).
> My questions:The 18 other pixels allow for the rise and fall time of analogue blanking
> 1. What are the other 18 pixels used for? Horizontal retrace, in the
either side of the 52 microseconds nominal,
and for any positional lee-way (mis-timing!) of the analogue video relative
to digital syncs.
There are 144 Y "pixel periods" of digital blanking period for H retrace,
Most MPEG video encoders work with a signal input that was originated
> 2. Are DVB broadcasts/European DVDs really 720x576 or actually
according to analogue standards.
So the occupied pixels of the digital active line are a nominal 702.
Some encoders pre-filter and downsample to fewer pixels. This softens the
picture, but reduces the input data per frame
to the compressor.
Aspect ratio calculations are made relative to the actual H width of the
> 3. Does the 4x3 aspect ratio currently used refer to 720x576 pixels or
analogue source picture, ie 702 pixels.
With 16:9 pictures, the 702 pixels still make 52 microseconds of analogue
waveform, but it is spread over 1/3 more
screen width for the same image height.
> 4. What about NTSC/US DTV? Are there 720 active picture informationTry www.atsc.org?
> pixels, or less?
> 5. Where can I get hold of ITU documentation? The EBU websiteRegrettable but true! Try www.etsi.org/BROADCAST/
> contains plenty of papers, but the ITU site seems to imply you need to
> be a paying subscriber :-
> Thanks for any informationCould I suggest a Digital Video Standards and Measurements course at BBC
Training, Wood Norton?!
Peter - my thoughts not necessarily those of......
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