iPad resolution is 2048x1536, 50% more pixels than 6 plus and about triple the 6's pixels. With iPad having a resolution way beyond HD, why aren't they marketed as HD?
401 PPI: iPhone 6 PlusGoogle's Nexus 9 has an 8.9-inch screen. The aspect ratio of the Nexus 9 is 4:3 like the iPad, and the resolution of the IPS display on the Nexus 9 is 2048 x 1536. This gives it a very healthy pixel density of 281ppi. The iPad Air 2 has a bigger, 9.7-inch display. Because of that bigger display its 2048-by-1536-pixel resolution means a pixel density of 'only' 264 PPI.
Resolution isn't what makes a display 'retina' or not, it is the pixel density number that Apple uses for that moniker. 326ppi is the minimum number Apple has used for the term 'retina'. I have included a table below showing which Apple devices make the cut. I have also added in the similar Nexus 9 (aspect ratio, similar size and display type) to show that it doesn't reach the criteria either.
401 PPI: iPhone 6 Plus
326 PPI: iPhone 4, iPhone 4S, iPhone 5, iPhone 5C, iPhone 5S, iPhone 6, iPod Touch (4th/5th gen), iPad Mini 2, and iPad Mini 3
281 PPI: Nexus 9
264 PPI: iPad (3rd/4th gen), iPad Air, and iPad Air 2
227 PPI: MacBook Pro (3rd generation) 13"
You're half right. It's the pixel density for a given viewing distance makes the display 'Retina' or not. If you re-watch the iPhone 4 keynote, it's quite clear the definition. All of those devices you listed, except this Nexus 9, has been referred to by Apple as including a "Retina" display. Starting with the iPad 3, it was referred to as the iPad with "Retina" display. And if you go to their website, the Macbook Pro Retina, is called such on almost every page.
So I don't know what you're getting at with this magic "326" ppi number, it's clearly defined as average viewing distance per pixel density. It goes by device category.
What the OP is asking is why they aren't called "HD" and I think the reason is to differentiate the screen quality on both the iPhone 6 and 6 Plus. It may be because the 6+ is the first to reach over 400 PPI but it's more likely just for market differentiation and because it is equivalent to an HD television, 1080p. And yes, Apple is not the first to do this on a phone, lol.
it actually probably has to do with the 6+ being 1920 x 1080 which is considered full HD in the TV world.
Isn't that what I said?
haha you did. I must have just stopped reading or something. I think I got caught up in the PPI talk.
iPad resolution is 2048x1536, 50% more pixels than 6 plus and about triple the 6's pixels. With iPad having a resolution way beyond HD, why aren't they marketed as HD?
They're all just marketing terms anyway.