iPhone 4 Retina Display
So we thought we’d do our best to clear this up for you.
Steve Jobs had this to say about the iPhone 4’s LCD display resolution during his WWDC keynote :
It turns out there’s a magic number right around 300 pixels per inch, that when you hold something around to 10 to 12 inches away from your eyes, is the limit of the human retina to differentiate the pixels.
Some blogs, spurred on by experts in the field of displays, have taken exception to Steve Jobs’ claim. Raymond Soneira, armed with a theoretical physics Ph.D. from Princeton University has gone away and done some maths based on angular resolution and stuff, and come up with a figure of 477 pixels per inch as being the theoretical density actually required for pixels to merge into each other at 12 inches from the human eye on an LCD panel.
This made me curious. How could Steve Jobs be so far out, and not expect to get called on it. The Retina Display only has 326 pixels per inch after all. That’s over 150 less than Soneira says is required for the capability that Apple claims the Retina Display has.
Now I don’t have a Ph.D., and can’t argue directly with Raymond’s figures, but I was able to find another person’s opinion, who I have reason to respect. He’s one of the scientists who works on the optics of the Hubble Telescope.
It’s certainly worth reading Phil Plait’s full explanation, and I have included a link at the bottom of this article if you want to go ahead and do just that. But for those that just want his final conclusion I will simplify it here.
The iPhone’s pixels at 12 inches from your face are 0.0031 inches across.
With absolutely perfect vision, you should be able to discern things as small as 0.0021 inches across. i.e. You could ace a fighter pilot’s eye-test, not just pass. And your eyesight would rival that of a bird of prey.
Well it doesn’t take a maths expert to see that a fighter pilot may well be able to see the pixels on an iPhone 4’s Retina Display.
But we are overlooking something quite obvious here. The majority of humans do not have absolutely perfect eye sight. In fact a surprisingly high number of them don’t even have 20/20 vision. Even with 20/20 vision (eyesight that does not require you to wear glasses) you actually can’t resolve anything smaller than 0.0035 inches.
Again, it doesn’t take a maths expert to see that people with 20/20 vision and below will not be able to discern individual pixels on an iPhone 4’s LCD.
Phil’s conclusion is as follows :
Aha! This means that to a more average eye, pixels smaller than this are unresolved. Since the iPhone’s pixels are 0.0031 inches on a side, it works! Jobs is actually correct.
In a slightly less scientific test I took a graph I have from when I chose my HDTV for my sitting room.
Now what this graph does is let you know how far away your HDTV can be from your sofa before you won’t be able to tell the difference between 480p, 720p, 1080p, or even 1440p. By extending the graph lines from the area that said I wouldn’t be able to see the difference between any display resolution. i.e. A normal TV picture would look the same to me as a 1440p HDTV, I was able to come up with a rough figure of 320 pixels per inch for an HDTV 12 inches from my nose, and the same size as an iPhone!
I can only assume that HDTV manufacturers want to sell HDTV TVs, and to sell the most expensive model possible, so have more than likely fudged the figures in their favour slightly. So if anything they would be trying to get me to buy a higher resolution HDTV than I really need. Even with their graphs they seem to confirm what Apple have been saying too.
In short, unless you have the eyesight of a bird of prey, rest assured that the Retina Display is going to look awesome.
So, who do you believe? A Hubble Telescope Engineer, Steve Jobs, or a pernickety guy with a Ph.D? Let us know your thoughts in the comments.
Phil Plait: [Full Explanation]