Display expert Raymond Soneira has a bone to pick with Steve Jobs. You know that little comparison Steve made between the human retina and the resolution of his "Retina Display" featured on the upcoming iPhone 4? It's wrong, he says.
Here's Soneira's take:
Steve Jobs claimed that the iPhone 4 has a resolution higher than the Retina — that's not right:
1. The resolution of the retina is in angular measure — it's 50 cycles per degree. A cycle is a line pair, which is two pixels, so the angular resolution of the eye is 0.6 arc minutes per pixel.
2. So, if you hold an iPhone at the typical 12 inches from your eyes that works out to 477 pixels per inch (ppi). At 8 inches it's 716 ppi. You have to hold it out 18 inches before it falls to 318 ppi.
So the iPhone  has significantly lower resolution than the retina. It actually needs a resolution significantly higher than the retina in order to deliver an image that appears perfect to the retina.
It's a great display, most likely the best mobile display in production (and I can't wait to test it) but this is another example of spec exaggeration.
It's not surprising that Apple exaggerates the capabilities of its display, a visually subjective pursuit where hyperbolic description of resolution (and especially contrast) attributes runs rampant.
We contacted Apple for a response, and we'll post an update if and when they do.
UPDATE: Nothing from Apple yet (not surprising), but Dr. Soneira had even more astute comments to add:
The iPhone 4 is actually very far from a retina display — it's a substantial discrepancy and not even close: At 12 inches the 1 dimensional linear difference is 326/477 = 68 percent. But the pixel (area) density for 2 dimensions, which is the actual relevant observable, is that value squared = 0.47, so the iPhone 4 is more than a factor of 2 from being a retina display at the typical 12 inch viewing distance. Stated another way the iPhone display would need to have 1.3 megapixels instead of 0.6 megapixels to be a retina display.
There have been some comments that my analysis is for perfect vision. Jobs' statement is for the *retina* not the *eye* with a poor lens. If you allow poor vision to enter into the specs then any display becomes a retina display. That turns it into a meaningless concept that will be exploited by everyone. The iPhone 3GS is a retina display too for good percentage of the population.
Specs need to be objective, precise and accurate. Allowing puffery and exaggerations in the sales and marketing starts a snowballing effect that eventually leads to the 1000% rampant spec abuse that I document for displays.
By the way, Dr. Soneira has a PhD in Theoretical Physics from Princeton University, and was a Long-Term Member of the Einstein Institute for Advanced Study in Princeton. Here's his bio.