Remember the original Palm Treo, released in 2002? Its flashy screen pushed the limits of resolution with 160 x 160 pixels. Then came liquid-crystal technology. The first iPhones all boasted 320 x 480, which has been more than adequate for the iPhone's estimated 21 million users. But not for long—the new iPhone 4G is out to best itself, with 960 x 640–pixel resolution for a 3.5-inch diagonal screen.
This ultra-high-resolution screen poses the question: Is Apple setting new standards that we can use—in this case, see—or is it ignoring human limitations and forging on regardless?
Companies keep shrinking pixels to make a clearer image, but human eyes are limited to finite levels of detail. "There's basically nowhere to go" for pixels in small screens, says Ethan Rossi at the Center for Visual Science at the University of Rochester, who believes the end of pixel improvement is near. After crunching the numbers, Rossi found that the iPhone 4 surpasses 20/20 human visual capabilities if we hold the phone at standard reading distance, about 16 inches away. At 1 foot, the iPhone 4 still outstrips our visual capabilities. Only at extremely close distances—within 10 inches*—does the iPhone's resolution begin to falter. At this point, a human with 20/20 vision would be able to see the array of pixels.
The issue is that our sight abilities are limited to the density of photoreceptors within the fovea, the center of the eye where vision is sharpest, which spans about 5 degrees of visual space. The number of cones (photoreceptors) in the fovea limits our resolution.
At the fovea, someone with 20/20 vision would resolve a little over 60 pixels per visual degree. Because we resolve images based on these degrees of visual angle, distance matters. Assuming iPhone users hold their phones a foot or more away from their faces, the clarity would indeed be "perfect." The farther the phone is from the face, the less degrees of visual space it occupies, meaning there are fewer photoreceptors to process the image.
The iPhone already touts itself as a "retina display," claiming to keep pace with the capacities of the human eye. But looking at any pixellated image from far enough away, whether it's the iPhone or an old iMac model, will make it appear perfect. The visual angles will end up wider than the pixels, which are invisible to the user at a distance. Up close, the perfection disappears.
Another bump on the path to perceiving Apple's high-quality display is the cornea and lens filtering system, called optics, that light passes through before it gets to the retina. Optics contain the most variability in the human eye. If we remove all defects in optics from the equation, Rossi argues in a paper published this year in Nature Neuroscience, human vision would surpass even 20/10—it would be closer to 20/8 or 20/7.
Because optics are the limiting factor in perceived clarity, optical perfection from newer forms of LASIK is likely the only way we will see gains from technologies beyond Apple's Retinal Display technology. Custom LASIK surgeries use advanced mapping system in order to assess the specific aberrations in individual eyes. This enables a nuanced surgery that can potentially push the eye's capabilities far past 20/20.
Hear that, ophthalmologists? Steve Jobs is tapping his foot.
*Correction: This story originally stated that the iPhone's resolution begins to falter "at about 3 inches," but according to Rossi, it is just about 10 inches when the size of the pixels match visual resolution for someone with 20/20 vision.
