Dr. Soneira sent us some additional information, clarifying some of the misconceptions flowing around in comments and on other sites. He wishes to stress that his comments do not mean that he thinks the iPhone 4 display (or the phone itself) is bad. On the contrary, he thinks the display seems like a significant step forward. Dr. Soneira's comments are only regarding the claim Steve Jobs made of 300 pixels per inch being all that the retina can distinguish at a distance of "10 to 12 inches." Dr. Soneira's update is as follows
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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 two dimensions, which is the actual relevant observable, is that value squared = 0.47, so the iPhone 4 is more than a factor of two 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 many other displays.