I suppose musings like this are very common among Apple haters. Basically the complaint boils down to:
“325dpi? Bah! Even a 1986-era laser printer does 300dpi and my newspaper does at least 600dpi. Until you get there, the print is smudgy and causes eye-strain.”
What a crock of shit.
First of all, hats off to Apple marketing for coming up with the name “retinal display.” It really sounds very high-tech—or, biotech.
Second of all, it isn’t 325dpi, it’s 325ppi. There are 3 pixels (subpixels) in a single visual color dot. With subpixel rendering the two can be seen as equivalent, but you have to remember that there will be color fringing that might be significant enough in certain instances to make the distinction significant. For instance, in a photo of a natural scene, you might not notice the pixelation, but a diagonal line, or looking at very small text—you will.
What is the significance of 325ppi? Pretty much that it’s a bigger number than 300 dpi. What is 300dpi? It’s an arbitrary benchmark from the print world.
As I’ve explained ad-nauseum, 300dpi is a well known number from printing circles. It‘s the acuity limit of most eyes at a viewing distance of 1 foot. This is physics and biology here.
What is going on is that your eye is a digital sensor in that it has individual elements (cells called photoreceptors) that sample light at discrete points in space. The closer packed these photoreceptors are, the more detail you can pick out. Now biology is no slouch so in the center of your eye, these things are packed really close. They’d be packed even closer except for one thing: light is a wave and its wave nature will dominate at a certain size scale when it passes through your pupil—this is what is meant by the word diffraction. Your eye’s biology is that good. It’s good enough biology that it nearly reaches the acuity limits dictated by this law of physics.
That’s the limit—you can’t do better than that without processing tricks and still be human.
This means that if the dots are close enough, or your viewing distance is far enough away, you aren’t going to see the dots.
At a viewing distance of 1 foot, that’s around 300dpi. Printers know this number well.
Actually, it’s worse
In reality, most people’s viewing distance or acuity is much worse than a computed value. Some people are farsighted or very nearsighted or don’t have perfectly corrected optics. Some people squint (which increases the diffraction). The lighting isn’t perfect, there may be reflections and refraction and the image may be distorted. Or maybe it’s just too dark and those acute cones in the center of your eye just can’t get enough data to make a decision. The dots in the test may not have enough contrast. Some people simply don’t have the time to stare at things forever to look for differences in detail. That’s why the megapixel myth is a “myth” and why you can do tests like this to prove it.
About that viewing distance
And really, is your average iPhone usage viewing distance 1 foot anyway?
Let’s put it another way. Do you notice the pixelation on your color monitor right now? Can you see the individual pixels in that form the font in this text? I can’t on my computer as I type this. Well if it’s a desktop LCD panel like mine, you’re only around 80ppi. My viewing distance is about 3 feet.
Perhaps you are reading this on a laptop. The resolution is much higher (up to 130ppi in some cases) and you are a little closer than three feet away. But you still can’t see the pixels.
Now think of your High Definition TV set. If it’s anything like mine, you have less than 30ppi when it’s showing a 1080p Blu-Ray, but it appears sharp as a tack. And, can you even see the difference between 720p and 1080p from your couch? I can’t.
After a while you start to notice that the dpi of your displays and the typical viewing distance form a relationship.
This is why I think the laptop example is best. That’s the viewing distance of how I use my phone the most and that means that 140dpi should be more than enough. The best complaint one can make about the Retinal Display is not that it’s not as good as print, but that you probably won’t notice the difference unless you’re looking for it. Eyestrain relief may be minimal or may only occur only after you’ve finished reading War and Peace on your iPhone.
Why we like print
Print is inefficient; newsprint is even worse. In a newspaper, you’d be lucky to get 86ppi effective resolution on the photos, and in many cases it’s much worse because ink is messy and smears and the paper it’s printed on is barely fit to line your birdcage with.
Not only that, there is more to things than acuity. There is also contrast and color. Print doesn’t do well in either regard because contrast is passive (depends on how how bright the ambient light is and how white the paper you print on is. Newspaper is not very white because white paper costs a lot) and ink doesn’t have a large gamut.
600dpi? Puh-leez. Any mention of dpi or ppi for “newsprint resolution” is the same old canard of using digital measures to misrepresent analog as being better simply because it’s analog. Effective resolution for most newspapers (for print) isn’t any better than my first laser printer: 300dpi Laserwriter in 1985.
The big difference with eyestrain is obvious if you’ve ever owned a Kindle. It’s active lighting vs. passively lit. All these displays we’ve talked about are backlit—a form of active lighting. Newspapers are passively lit, which is very different.
Think of it this way: you merge the red green blue lights of your display together and what color do you get? White. But you merge cyan, magenta, and yellow paint on paper together and what color do you get? Black. It’s additive vs. subtractive color.
The ambient light levels needed to give contrast to read print on newspaper is the same as the light levels of ambient light! The light levels needed to light the back of your computer LCD to provide adequate contrast is much greater than the ambient light. Don’t believe me? Take a photo of your desk with your computer on. You’ll notice that the monitor will be blown to the highlights. Or think of it this way: the black in the blackest black of your monitor is no blacker than your monitor when it’s off (it can’t be), but it appears much blacker!
Your eye is constantly scanning and your iris is instinctively adjusting for the local contrast of what you’re looking at: as the eye center shifts from your monitor to your office, the muscles in your iris instinctively open your pupil. As your eye shifts from your office back to work, those muscles instinctively stop down. Doing that all day is tiring.
For book print and eInk, the ambient light and contrast light are the same light. Your iris doesn’t need to adjust and you have no problem. A corollary to this will be that if you have the exact same eyestrain with a itty bitty booklight on a Kindle (or a paper book) at night as you would with an iPad at night. Factor in the inconvenience of those book lights and you start why sales seems inextricably tied to Christmas—when you’re giving those to someone else.
In summary, the argument against the new display should be, you’re not going to be noticing the difference (unless you look for it), so why didn’t they put an OLED display and give us even more battery life instead? Or just sell an option without the display.
Aside: The Kindle
Yesterday, I asked Matt if he still uses his Kindle now that he has an iPad. He said he does, because he reads a lot outside. The iPad has no contrast outside. (You’ll also notice the same contrast problem with your computer in an office with a lot of window lighting in morning or evening light because of the glare or reflections. Or try to use your laptop outdoors.)
As for me, my landlord was amused to find out I’m hardly using my Kindle anymore (I still use the Kindle app). I am surprised at how great the iPad’s battery life is and how important fast pagination of a non-eInk display is for reference material. If my New Yorker subscription were available on the Kindle App, I’d seriously consider getting rid of my Kindle 2. Well that and the an ability to do text exports of my marks would be nice. 🙂
At lunch yesterday, Mike mentioned that he was surprised that Apple didn’t go with OLED because of the longer battery life.
I said that, while it should half the battery drain issues in theory, in practice, it isn’t that great, so Apple probably opted for the thing that’s going to sell better and be unique (resolution) over something nebulous as that.
He said that in testing, he found that the display eats the most power of nearly everything on the phone and that OLED equipped Android phones lasted much longer on a single charge. I postulated that they may just have a bigger battery in them because the technology hadn’t reached the point of efficiency.
In any case, worried that I had been spewing bullshit, I looked it up:
While an OLED will consume around 40% of the power of an LCD displaying an image which is primarily black, for the majority of images, it will consume 60–80% of the power of an LCD – however it can use over three times as much power to display an image with a white background such as a document or website. This can lead to disappointing real-world battery life in mobile devices.
(Clearly, there will be a point where Apple will switch, but they’re not there yet.)
In talking to friends, I realized that I left a lot of things to infer that I should have summarized better:
Most of the time, you won’t notice the difference between the new display and the old one. The exceptions are
- You have the two side by side. In that case you’ll naturally pull up very close to both to make the comparison
- You are examining looking at details in a photo or artwork. In this case people often bring it very close, even if they’ve pinch zoomed.
- You are reading a book on the iPhone. In that case your viewing distance will be about 1 foot away
- You are texting. Some people text at about a foot and a half which is just enough to notice a difference between the current iPhone and this one (but not so with the Android).
The reason your eyes get tired while reading has very little to do with resolution and almost to do with active vs. passive lighting.
- Almost all displays are actively lit (this means that they start out “black” and provide contrast by lighting it up). This includes CRTs, Plasma TVs, color LCDs, LED-backlit LCDs, and OLEDs.
- For them to provide proper contrast, actively lit displays must be much brighter than the ambient lighting. You look away from your monitor and the iris muscles work to deal with the differing lighting conditions which tire out your eyes.
- Books, B&W LCDs (digital watch faces), and eInk displays (Kindles) are passively lit, This means they are lit by the ambient light and provide contrast by subtracting from it (with paint).
- Your eyes don’t have to adjust to a change in lighting because the lighting is the same.
- This also explains why Matt still uses his Kindle: In outdoor or daytime lighting, actively-lit displays can’t overpower the sun and have little to no contrast. (Those new digital billboards have very bright LEDs that can.)
What I think happened with the Retinal Display was the following. From a business perspective, Apple needed to increase the resolution of the iPhone to compete with Android phones that have high pixel densities—high enough to cover the texting case above. Since a computer is fundamentally binary, it simplifies computation and design (allowing almost no changes for the developer or loss in performance) if they simply double the pixels the display in both directions (4x the pixels in the same sized display). Doing so caused them to greatly overshoot what is necessary (and probably forced the choice of LCD over OLED). However, they noticed the number they reached (325ppi) happens to be greater than a known reference in printing circles (300ppi)—the maximum effective necessary resolution at reading distances. Since their competition has not reached that resolution, they marketed it as “retinal display” and used that catchy term to educate consumers to demand something they probably don’t need.
If you are an Apple hater, it may sound evil. But then again, I don’t need to pay $3 for coffee either.
Need and want are two very different things. 🙂