[opendtv] Re: 3D compressed formats
- From: "Manfredi, Albert E" <albert.e.manfredi@xxxxxxxxxx>
- To: "opendtv@xxxxxxxxxxxxx" <opendtv@xxxxxxxxxxxxx>
- Date: Fri, 17 Dec 2010 17:02:22 -0600
Mark Schubin wrote:
> Before I get into all the options, let me start by saying that
> almost all of the 3D being transmitted today uses a straight
> side-by-side squeeze: both views squeezed horizontally by a
> factor of two and placed side-by-side in a single frame. That's
> one of the HDMI 1.4a formats. The compression of those
> side-by-side images is standard.
>
> Of course, there's a loss of 50% of the horizontal resolution, so
> Dolby recommends a variation in which the left-eye image takes
> alternating columns of pixels starting with the leftmost, and the
> right-eye-image takes alternating columns of pixels starting with
> the next column. That way, for portions of the image with no
> disparity, there's at least the possibility that the two eyes'
> resolution can be additive (although, once the temporal element
> of shuttered glasses is added, all bets are off.
>
> Although that's the most common, it's just one form of
> "frame-compatible" compression. In side-by-side, alone, in
> addition to the simple squeeze, there are: squeeze & mirror;
> rotate & squeeze; and rotate, squeeze, & mirror. Then there are
> side-by-side versions based rotated 720p in a 1080p frame, thus
> losing both horizontal & vertical resolution, but less of each,
> and there are mirrored versions of those, too. There is also
> over-under (with mirrored version), alternating field, alternating
> frame, column interleave, line interleave, and quincunx, plus the
> Sisvel tile format (a full-sized, left-top, 720p image in a 1080p
> frame with the right-eye view broken into pieces surrounding it),
> something that allows set-top boxes to deliver 2D from a 3D
> transmission without doing image processing. Finally (in
> frame-compatible compression), there is anaglyph, with MANY
> color-pair combinations, of which the most popular are red-cyan,
> green-magenta (Trioscopics), and blue-amber (ColorCode 3D &
> SpaceSpex).
>
> That brings us to non-frame-compatible (sometimes called service
> compatible). One form takes any of the (non-anaglyph) versions
> above and adds a helper signal for restoring the missing
> resolution. Then there is 2D+delta (the difference signal
> representing the disparity of the two views), 2D+delta+graphics,
> 2D+depth, 2D+depth+graphics, and 2D+depth+graphics+graphics
> occlusion. The +depth formats are useful for multiview
> autostereoscopic displays.
As far as I can tell from this detailed and concise description, most of the
interest seems to lie in "frame compatible" formats. Although they all reduce
resolution and they are all incompatible with legacy 2D displays.
I didn't even know about the "2D+delta" format, but IMO, that ought to be the
clear winner. Just like color TV and just like FM stereo, that signal is
compatible with legacy 2D displays, and it only reduces resolution if the
distribution pipe is not wide enough. The pixel count in the main image does
not need to be reduced, because the difference signal is not squeezed into the
same frame as the main image.
So, if you use 9 to 10 Mb/s for the main 720p24 HDTV transmission, legacy
displays will show HDTV. The difference signal can take up about the same
amount of bandwidth, and stat mux will help too, and the new 3D receivers will
get their glorious 3D. Ditto for optical discs, I would think, where there
ought to be enough capacity to handle the main and difference signals, and 2D
players can continue to function just fine.
And also, I don't know if this is true, but maybe you can save a little extra
by reducing the bandwidth of the diffrence signal? Sort of like you can do with
Y Pb Pr color, where the bandwidth of the Pb and Pr combined can less than the
bandwidth of Y, and still creating good color images?
Bert
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