Originally Posted by caliminius
The iPad is 1024:768, a 4:3 aspect ratio. 720P HD is 1280:720 (256 pixels wider than the iPad), a 16:9 aspect ratio. Thus the iPad can't handle HD properly. Thus NOT proper HD. Please get your facts straight.
Hmm...this topic again.FACT: iPad can display 16:9 720p H.264 content at 1024x576 natively. This is not HD.
When NHK first developed the HD spec there were two key criteria:
FACT: To get 30 degrees HVA at 60 PPD for the "true" HD effect you need a minimum of 1080p resolution.
- The display resolution has sufficient pixel density that a person with 20/20 vision would no longer see pixel structure. This is 60 pixels per degree (PPD) based on human visual acuity.
- The display size was sufficiently large to provide the same immersive effects of cinema. This was determined to be 30 degrees of horizontal viewing angle (HVA). This is known as the induction effect. 
This is roughly equivalent to sitting in the furthest seat in a movie theater that meets SMPTE or THX specs. More is better unless you like sitting way in back but no mainstream home theater product does this.
720p is part of the HD spec, is considered HD but doesn't actually meet the original objectives of replicating the high def theater experience in the home (aka "home theater").Opinion: What this means on a practical level is any display that isn't at least 1080p is simply some level of compromise to the minimal requirements for high def viewing.
Analysis: iPad and meeting the high def movie experience
Assuming 1024 horizontal and a 1 ft viewing distance it comes out to:
23.97 pixels per degree for 2.39:1 movies
25.13 pixels per degree for 1.85:1 movies
25.37 pixels per degree for 1.78:1 (16:9) movies.
To get 60 PPD (aka full HD) density you need to sit 2.37 feet away (16:9)
To get the 30 degrees HVA you need to sit no more than 1.31 feet away.Like all other displays that does not meet the 1080p resolution the iPad cannot meet both 60 PPD and 30 degrees HVA. This includes 720p HDTVs and any other 720p class slate.PROBABLE FACT: There are no currently produced or announced 10" slates that can natively reproduce "real" HD at 60 PPD and 30 degrees HVA.
I say probable because while I'm not even sure anyone mass produces a 10" panel that is 1920x1080 res or higher and I would have remembered anyone spec'ing a natively 1080p slate at CES this year (there are some that output 1080p but not natively show it) I'm not 100% certain.
If I'm wrong I'm sure someone will correct me but at best I'm saying no 10" slate does better than slightly higher than 720p at 1366x768. And those are probably 11.1" panels.Factoid: Most folks sit about 8+ feet from a 50" 1080p TV which results in a 14.55 degree HVA at 73 PPD.
I would list this as a fact except I can't find the damn study again to list as a reference. This article says 10' but there was an Italian study by one of their major national TV stations that stated around 8'. It'll vary by country (and the average home size in that country) but 8' is what I recall to be on the lower end of the spectrum.http://www.hometheatermag.com/gearwo...rez/index.html
Anything above 60 PPD you can't generally see unless your vision is above 20/20. This is NOT HD because you're sitting too far away to get the induction effect. Most folks with HDTVs are missing out on the real home theater experience.
Remember that to get 60 PPD you need to be 2.37 feet from the iPad. The HVA at that distance is 16.91 degrees at 60 PPD. 16.91 is bigger than 14.55.CONCLUSION: At the optimal 2.37 foot viewing distance for the iPad it appears larger than a 50" 1080p HDTV at the normal 8+ foot TV viewing distance and has the same usable resolution for people with 20/20 vision.
There is some debate on whether 60PPD is a sufficient minimum for 20/20 vision but that's the current spec.
Those are the facts, probable facts and the analysis based on that data. For all intents and purposes the iPad is what most folks consider to be a HD experience.
That most folks aren't really getting a HD experience is something only videophiles bicker (or snicker) about.
Now I just hope I got all my math right at 3AM.
 Psychophysical Analsys of the "Sensation of Reality" Induced by a Visual Wide-Field Display
by T. Hatada, H. Sakata and H. Kusaka, SMPTE Journal, Volume 89, pages 560-569, August 1980 retrieved 20 MAR 2010