The screen on the iPhone 4, dubbed the "retina display" by Apple brass, is the highest resolution display ever mass-produced on a phone. This doesn't mean that it has the most pixels of any display ever made (even for a phone), however it does mean that the screen has the most pixels per square inch of any other portable consumer display in history (Apple).
Just in case you haven't yet learned what exactly a pixel is, it's basically a dot of color on an electronic screen (TV, monitor, phone display, and so on). The way each type of display works is radically different from the next, but they all operate under the same principle of faux-mixing primary colors. If you zoom in close enough to any display, instead of seeing single squares of color you'll see groups or rows of red, green, and blue dots (red, green and blue are the primary colors of light). Because the dots are so small, if all of the red and blue dots on the screen are activated the screen will look 100% purple because these little dots, or sub-pixels, are generally too small to see individually unless under extreme circumstances like sitting a foot away from a giant plasma screen to watch the Superbowl.
Here's what a blank white screen looks like up close (meaning red, green, and blue sub-pixels all set to maximum) on the iPad:
The white lines were drawn in for illustrative purposes to show where each square pixel is actually situated in relation to its neighbors (Bryan Jones, Ph.D., 2010).
Think about it this way: that super-awesome 1080p HD TV you have sitting in your living room is 1,080 pixels tall and 1,920 pixels wide, meaning it has a total of 2,073,600 pixels spread out over the entire screen. Let's assume you have a fairly average 42" screen. The dimensions of a 42" screen (which is measured diagonally from opposite corners of the display itself) are about 37"x 21" for a total of just over 753 square inches of viewable real estate.
Do the division of 2,073,600 pixels over 753 square inches and you get 2,754 pixels per square inch. That sounds incredibly high, but walk up close to the TV and not only will be able to easily see each individual pixel, but you'll even be able to see the black space IN BETWEEN each little dot. That's because while 2,754 is certainly an impressive number, but it's not the number that matters.
Have you ever gone to print out a photo on your computer and seen an option for "DPI" in the settings? DPI stands for "dots per inch" in print media and the display equivalent is PPI, or "pixels per inch" - same concept, just with a dot that glows instead of a dot made of ink. Generally, the default setting for printing documents and photos is about 72DPI and a high quality print is usually considered to be 300DPI.
"But hold on! That sounds a lot lower than the 2700 pixels per square inch on the big TV screen!" Yes, it sounds a lot lower, but the trick is to remember that we left the units for the TV at SQUARE inches, not simply "inches." To fix this, we need to take the sqaure root of 2,754 to find the PPI of the TV, and in this case it comes out to just 52 pixels-per-inch.
This sounds like a lot still, but there's a reason that 300dpi prints are considered to be high quality. The reason is that a human eye with 20/20 vision can make out, at best, about 287 dots-per-inch on average (measured from one foot away), so anything around 300 dots or pixels per inch is right at the threshold of human visual acuity (Bryan Jones, Ph.D., 2010). Anything more and most people wouldn't be able to tell the difference anyway, so 300dpi has been a print standard for quite some time.
Let's get back to the new iPhone. It has a 960x640 pixels display, and the screen itself is just 3.5" across, or 2" by 3" along the sides (Apple). This means it has a whopping 102,400 pixels per every square inch of screen. That's 37 times as many pixels per square inch as on that super-awesome 42" HD TV. Take the square root of 102,400 and you end up with 320ppi, which is a higher number than even the high quality prints I discussed earlier. (It's important to note that the official ppi measurement for the iPhone 4 screen is 326ppi, because the screen is actually a little bit smaller than 2" by 3".)(Apple)
There are some academic debates over the Apple claims of the iPhone having a true "retina display" because of the fact that the human retina itself is more sensitive than what the screen displays (Cross, 2010), but because the lenses in our eyes slightly degrade the images we see as they're focused, the display is still just above the limit of what an average human can actually see (Myslewski, 2010). Maybe a more accurate name for the screen would be the "acuity display" but the current name still gets the point across to the consumer in the end: the new iPhone screen is really super sharp.
(In the interest of full disclosure, I own an iPod Touch, but am committed to the Android line for my smart phone. My computer is a Windows 7 machine.)
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Cross, J. (2010). Does the iPhone 4 Really Have a "Retina Display"? (Updated). Retrieved August 30, 2010 from PC World, pcworld.com: http://www.pcworld.com/article/198402/ does_the_iphone_4_really_have_a_retina_display_updated.html.
iPhone 4 Technical Specifications. (2010). Retrieved August 30, 2010 from Apple, apple.com: http://www.apple.com/iphone/specs.html.
Jones, B., Ph.D. (2010). Apple Retina Display. Retrieved August 30, 2010 from JonesBlog, prometheus.med.utah.edu: http://prometheus.med.utah.edu/~bwjones/2010/06/ apple-retina-display/.
Myslewski, R. (2010). Neuroscientist: iPhone 4's 'Retina display' not bullsh*t. Retrieved August 30, 2010 from The Register, theregister.com: http://neuroscientist: iphone 4's 'retina display' not bullsh*t.
Retina Display. (2010). Retrieved August 30, 2010 from Apple, apple.com: http://www.apple.com/iphone/features/retina-display.html.
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