[opendtv] Re: HDTV Buyer's Guide 2008
- From: Craig Birkmaier <craig@xxxxxxxxx>
- To: opendtv@xxxxxxxxxxxxx
- Date: Thu, 24 Jan 2008 14:20:32 -0500
At 12:14 PM -0500 1/24/08, Manfredi, Albert E wrote:
The one *possible* excuse for writing 1080i is the vertical interlace
scheme of some displays, where the 1920 pixels are painted in two groups
of 960. It's a stretch to call that 1080i. Maybe 1920i makes more sense.
I do not know of any display that ever did this.
The ALIS technology was a cheap way to scan a plasma panel using
traditional interlacing techniques. IN essence they scan 540 lines
per field then shift the fields up and down one pixel for playout.
Most of the time, all 1080i seems to mean is that the input signal, e.g.
HDMI, cannot reach 1080 at 60p. If I decipher the confused marketese
correctly.
Actually, I think the new versions of HDMI can go well beyond 1080@60P.
From Wikipedia: http://en.wikipedia.org/wiki/HDMI
Devices are manufactured to adhere to various versions of the
specification, where each version is given a number, such as 1.0 or
1.3. Each subsequent version of the specification uses the same
cables, but increases the throughput and/or capabilities of what can
be transmitted over the cable. For example, previously, the maximum
pixel clock rate of the interface was 165 MHz, sufficient for
supporting 1080p at 60 Hz or WUXGA (1920x1200), but HDMI 1.3
increased that to 340 MHz, providing support for WQXGA (2560x1600)
and beyond across a single digital link.
The problem is that MPEG-2 decoders cannot deal with pixel clocks
above ~62 Mpixels per second. Enough for 1080@30i and 720@60P, but
only half of what is needed for 1080@60P.
Today 1080i is typically de-interlaced after decoding and displayed
either as 720@60P or 1080@60P.
Regards
Craig
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