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From: bartbrn on 23 Jul 2010 13:26
27" iMac owners or prospective owners, especially those who THOUGHT
they could use their 27" iMacs, with the proper HDMI-to-Mini
DisplayPort Converter, as HD (1080p) TVs, PLEASE read this message --
at least the first three paragraphs -- and if you care about this
problem, please send feedback to Apple.

This message is about the existence of, and reason for, the 27" iMac's
Mini DisplayPort's inability -- AS AN INPUT PORT -- to accept or
display any resolution on the 27" iMac's display other than 1280p x
720p (and definitely NOT the 1080p -- aka "HD" -- that the Apple
Store's description of Belkin's AV360 HDMI-to-Mini DisplayPort
Converter SAYS it will). This is a known problem to Apple Engineering,
they KNOW it's the "crippled" EDID protocol at the Mini DisplayPort's
input, and the fix MAY be as simple as a firmware upgrade.

The Apple Techs I've spoken with (thank God for AppleCare!) have all
told me the same thing: get as many people as possible to send Apple
feedback asking for the Mini DisplayPort to be able to accept, and the
27" iMac to be able to display, 1080p (or higher) from HDMI device
signals processed through an HDMI-to-Mini DisplayPort Converter. The
Apple Techs assure me that Apple takes customer feedback very
seriously, and if enough people ask for this problem to be fixed --
the more feedback comments they get on this specific problem -- the
likelier they are to implement a fix. And it IS a problem: while most
game console outputs top out at 720p, and for the few consoles capable
of 1080p, by the very nature of game graphics, 720p doesn't look
noticeably different from1080p, the same is NOT true of Blu-ray or DTV
output. At normal computer-display viewing distances of 2 to 4 feet,
the the image degradation between 1080p and 720p is VERY noticeable.

The problem and the probable cause:

I bought my 27" iMac largely on the basis that I'd be able to connect
HDMI devices to the 27" iMac and get full HD (1080p) on the iMac's
display, as Apple's 27" iMac advertising, and their description in the
online Apple Store of Belkin's AV360 HDMI-to-Mini DisplayPort
Converter, suggests is the case. Apple's description however, leaves
out one VERY important fact, that is CLEARLY stated on Belkin's web
page for the AV360 Mini DisplayPort Converter: "Accepts full 1080p
signal, PROVIDES 720p TO iMAC." According to tested.com, the very
similar (in function AND $150.00 price tag) Kanex XD, actually OUTPUTS
1080p to the 27" iMac's Mini DisplayPort, but the Mini DisplayPort's
EDID implementation allows only 720p to be displayed.

Putting aside "truth in advertising on Apple Store" arguments for the
moment, the bottom line is that you CANNOT get full 1080p (let alone
the 27" iMac's highest display resolution of 2560 x 1440) through the
Mini DisplayPort. The best you can get, with ANY HDMI to Mini
DisplayPort adapter, is 1280 x 720, exactly HALF the full resolution.
It is NOT the fault of the adapter; the fault lies in Apple's
implementation of the EDID spec. Here's what tested.com says about
this situation:

<< An iMac can only accept 720p video through the device; while the 27-
inch iMac's screen supports 2560 x 1440 resolution, it can only
display half that when using an external video source. Kanex says this
is because the iMac supports external display identification data
(EDID) at two resolutions: 720p and its native resolution. Without the
necessary EDID support, It simply can't accept a 1080p video feed. The
21-inch iMac's native resolution is good, old-fashioned 1080p, but it
can't process any video input through the mini DisplayPort.

<< This limitation really puts a damper on the 27-inch iMac as an
HDTV. Blu-ray Disc players, PlayStation 3 systems, and Xbox 360
systems can all output at 1080p video. The iMac screen supports well
over 1080p resolution. The Kanex XD can actually process 1080p video
through the mini DisplayPort. The bottleneck is on the Mac's side, and
it's a very strange one to have. >>
------------------------------------------------------------------

The documentation:

Here's the Apple Store's description of Belkin's AV360 Mini
DisplayPort Converter, in part:
------------------------------------------------------------------
The Belkin AV360 Mini DisplayPort Converter lets you connect any HDMI
device such as a PS3, Xbox, or Blu-ray Disc player to the Mini
DisplayPort on your 27-inch iMac—so you can use the screen to play
video games or watch movies.

* Compatible with Xbox, Blu-ray Disc player, DVR
* Full audio and video support
* Provides resolutions up to 1080p
* USB powered
* Scales resolution to fit the entire iMac (supports 480i, 1080i,
480p, 720p, 1080p resolutions)

Mfr. Part No.: F2CD007
------------------------------------------------------------------
BUT, on Belkin's own web page (http://www.belkin.com/
IWCatProductPage.process?Product_Id=508267) for the AV360 Mini
DisplayPort Converter (Belkin Part No.: F2CD007), Belkin's description
clearly states:

* Accepts full 1080p signal, PROVIDES 720p TO iMAC
* Delivers stereo audio

AppleInsider, tested.com (http://www.tested.com/news/kanex-xd-opens-up-
your-imacs-displayport-to-hdmi-input/426/), and electronista.com
(http://www.electronista.com/reviews/kanex-xd-for-27-inch-imac.html),
among others, have reviewed both the Belkin AV 360 and Kanex XD HDMI
to Mini DisplayPort Converters

"Full audio and video support," as Apple Store's extremely misleading
blurb suggests, not only is the iMac display limited to 720p with this
adapter, the "full audio" turns out to be nothing but standard stereo.

From Tested.com's review of the Kanex XD:

"The $150 box serves as a bulky bridge between a home theater device
like a Blu-ray Disc player or a video game console and the iMac. It
requires its own power supply, but since you're hooking it up to an
iMac you can use the power outlet you save by not having a separate
monitor. Since it converts HDMI signals, it transmits both video and
audio to the iMac and can pipe out video game and Blu-ray Disc sound
straight through the iMac's speakers with a single cable.

"Unfortunately, there's a bizarre hitch, and it doesn't seem to be the
Kanex XD's fault. An iMac can only accept 720p video through the
device; while the 27-inch iMac's screen supports 2560 x 1440
resolution, it can only display half that when using an external video
source. Kanex says this is because the iMac supports external display
identification data (EDID) at two resolutions: 720p and its native
resolution. Without the necessary EDID support, It simply can't accept
a 1080p video feed. The 21-inch iMac's native resolution is good, old-
fashioned 1080p, but it can't process any video input through the mini
DisplayPort.

"This limitation really puts a damper on the 27-inch iMac as an HDTV.
Blu-ray Disc players, PlayStation 3 systems, and Xbox 360 systems can
all output at 1080p video. The iMac screen supports well over 1080p
resolution. The Kanex XD can actually process 1080p video through the
mini DisplayPort. The bottleneck is on the Mac's side, and it's a very
strange one to have.

This doesn't mean the Kanex XD is useless, though. At 27 inches, even
720p video looks quite good, even if it isn't as crisp at 1080p video
and doesn't come close to the displays maximum resolution. Since the
iMac doesn't play Blu-ray Discs and the Mac video game library is
still very small, the ability to connect a game console or Blu-ray
Disc player at any HD resolution is a boon. A $350 Playstation 3 and a
$150 adapter can give the $1,700 27-inch iMac some much-appreciated
media flexibility. If you don't have the room for a full home theater
system, it lets the iMac pull double-duty as a computer and HDTV. It's
a pricey solution, but so's the 27-inch iMac to begin with."

CNET's review of the Belkin AV360:

Belkin AV360 Mini-DisplayPort converter for 27-inch iMac

June 29, 2010 | 9:31 AM PDT

The Good: Bridges the gap between 27-inch iMac and HDMI video
components; simplifies set up by scaling video to match the iMac's
720p input limit, regardless of source setting; USB-powered, which
minimizes cable clutter.

The Bad: Won't input HDMI-equipped PC video to the iMac; no support
for 2,550x1,440 native iMac resolution.

The Bottom Line: Belkin's AV360 iMac adapter edges out the competition
by making it easier to connect HDMI-based video components to your
iMac's Mini DisplayPort. We'd prefer that Apple had gone with HDMI in
the iMac to begin with, but until it makes that switch, this is the
adapter we'd pick.

electronista's review of the Kanex XD:

Review: Kanex XD for 27-inch iMac
Kanex lets iMac owners turn their screen into a TV. (May 8th, 2010)
The Kanex XD is in theory the dream device for apartment dwellers, or
just those who don't want to buy a separate TV: it turns the 27-inch
iMac into a full-fledged TV for anything that works with an HDMI
input, such as a PlayStation 3 or even your cable set-top box. At
$150, however, is the feature set good enough to have you abandoning
conventional TV sets? We hope to find out in a full review.

Price: $150

The Good
* Good image and audio quality.
* No visible lag.
* Simple setup.

The Bad
* No 1080p or surround audio.
* Expensive.

What's included and setting up

There's not much to bundle in the box with the XD, but thankfully
Kanex has included what arguably matters the most. Besides the
essential power adapter, the box hides both a 3-foot Mini DisplayPort
(miniDP) cable and a 3-foot HDMI cable. As such, it's not hard to get
started even if your source equipment doesn't have a bundled HDMI
cable; the modern PS3 and Xbox 360 are the notable examples where this
becomes distinctly useful. That said, the short cable length means
you'll still be shopping for a longer HDMI cable if the source can't
sit close by; any set-top boxes you use will probably have to sit on
the desk itself.

Connecting it all up is, not surprisingly, quite simple. About the
toughest part was plugging the miniDP cable into the iMac itself,
which required more force you'd suspect. Kanex rather thoughtfully has
lights on both ends of the adapter, so you'll know if the miniDP cable
or iMac isn't receiving the signal even if the XD can tell its HDMI
source is working.

By far the most appreciated touch is simply the nature of the format:
because you're converting from HDMI to miniDP, both of which support
audio on the same signal, there's no separate audio cables to plug in.
It would be nice if there was the option to route audio separately --
some may want to bypass the iMac entirely for this -- but the
simplicity is hard to argue.

There aren't any manuals, but Kanex is quick to point out that a quick
Command-F2 shortcut will switch back to the iMac's main display.
That's really all that's needed and a definite time saver given that
few will unplug the XD every time.

The one obstacle is simply the plugin order. To get the "best
results," Kanex recommends that you first power the device, then
connect to the XD and finally link the miniDP cable. It's logical, but
if you have to reconnect often it could get to be a nuisance.

Performance

When everything is set up properly, the Kanex XD largely works as
advertised. The all-digital signal shows no noticeable degradation or
scaling artifacts, and audio comes out at a good volume and quality.
We didn't detect any tangible audio or video lag with a PS3 or a Zune
HD AV dock. That's especially important for PS3 and Xbox 360 gamers
who might lose in a fighting game due to any significant delay between
their input and what's on screen.

It's here, though, that we encounter the XD's primary limitation: its
maximum 720p resolution for many HDMI sources. Despite the iMac
supporting up to 2560x1440 on its own, you're reduced to just a
quarter of that resolution (1280x720) for the actual signal. We can
somewhat understand why this is, since 720p scales neatly on the
iMac's display, Kanex doesn't have to do elaborate scaling for the
output to look correct. For the PS3, Xbox 360 and Zune HD, this won't
be much of an issue since they rarely if ever output above that
resolution. For Blu-ray players and other 1080p-capable devices, it's
a major inconvenience; you're only sitting 2-3 feet away in normal
situations, so you'll notice the imperfections of 720p much more than
you would with a TV.

The limitation is hard-coded, too. We tried plugging in our PS3 while
it was configured for 1080p, and it simply generated a blank screen.
This admittedly isn't likely to happen if you're setting up the PS3
for the Kanex adapter first or if you were already using 720p, but it
can be a definite hassle. Combine that with the spec's current
limitation to stereo audio and you won't quite have a real home
theater experience.

Before we criticize Kanex too harshly, we should note that some of the
fault here is Apple's current implementation of the 27-inch display's
resolution modes. As of this writing, the EDID (Extended Display
Identification Data) for the screen will only accept 16:9 aspect ratio
input in either the iMac's native resolution or 720p. The Kanex XD
therefore can accept 1080p -- but not from an iMac. It doesn't change
the reality for the end user but does mean the add-on could get more
advanced resolutions with future iMac firmware updates, if any.

Wrapping up

Kanex is very forthright with what the XD does and makes it as easy as
possible to get started. If you're in a studio apartment and your
choice is either a 27-inch iMac or a 27-inch TV, you can get the
adapter knowing it should accept most current HD properly and will
save you both some cash and some space.

The operative term is, of course, "most." For $150, it's somewhat
disappointing the adapter won't change resolution to accommodate
1080p. What the adapter does now is good for many purposes, but we can
see a point a few years into ownership where the Kanex XD is made
obsolete by newer consoles or 1080p-plus TV sources.

It's still a definite success as an adapter, but don't expect to never
need another adapter again.
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