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Do you really need 300 PPI on a 3.5 inch phone?

By 8 June 2010 42 Comments

Update June 9 2010 – Let me be very clear that I am not suggesting that there are no benefits to the new Apple iPhone 4 “Retina Display” in this post.  Not only is it a superb display and a massive improvement over the old iPhone and most other phones on the market, I’ve made it clear that the iPhone 4 is overall a revolutionary device.  So this is not a bash iPhone post by any measure.  What I am saying is that compared to a larger OLED screen with the slightly lower resolution of 800×480, the iPhone 4′s display is not advantageous for people who hold their phone more than 13 inches away from their eyes.  I am also not suggesting that no one holds their phone closer than 13 inches.  What I mean is that I don’t see many people holding their phone within 13 inches, and that we cannot discount the size advantage and superior contrast ratios of OLED over IPS technology.

Aside from the dubious advertising on the iPhone 4′s “Retina Display” where Apple grossly inflated the quality of the display, I was very surprised to see Apple use such a high resolution on such a small display.  Apple claims that 300 Pixels Per Inch (PPI) is the limit of the human eyes when viewing something approximately 11 inches away from the eyes, and that the iPhone’s 326 PPI beats competing Smartphones with only 252 PPI.  But how advantageous is 326 PPI in real life when most people typically hold the phone at 13 inches away or more?

If we look at figure 1 below, I illustrate how viewing distance (distance between phone display and your eye) affects the maximum PPI detectible to the eyes.  If a display with half the PPI is held at twice the distance, it will appear as though the pixels are the same size which results in the same angular pixel density measured in Pixel Per Degree (PPD).  This is the same reason your finger can look as big as the moon when you hold it in front of the moon at the right distance from your eyes.

Figure 1 – Effect of distance on PPI and angular pixel density
Effect of distance on pixels per inch and angular pixel density
Image credit: George Ou

So if Apple claims 300 PPI is the limit at 11 inches (and the theoretical limit is 50 cycles per degree), then 252 PPI is the limit at 13 inches viewing distance.  When I observe the majority of phone users, most people hold the phone more than 13 inches away from their eyes because it strains the arm and possibly the eyes when it is forced to focus at such a short distance.  For my eyes (which are better than 20/20), 6 inches seems to be the minimal focal distance although it is a strained focus and requires me to cross my eyes.

So the numerous smart phones with 252 PPI 3.7″ (and soon larger) displays are actually not at a disadvantage in terms of pixel density beyond 13 inches viewing distance.  Beyond 13 inches of clearance, the size of the display is far more important than the PPI.  In fact, many users would consider size to be more important than PPI even if they can see the pixels.  Furthermore, those 3.7″ displays based on OLED technology generally have better color and contrast ratios than the IPS display that Apple uses and it’s the reason OLED costs far more than IPS.  OLED technology is so expensive that the 11″ Sony XEL-1 HDTV is still over $2000 which is twice the price of 40+ inch IPS HDTVs.

So while it’s possible that some consumers will benefit more from the iPhone 4′s 326 PPI display because they hold it within 13 inches of their eyes, prospective buyers should consider their own viewing habits and examine the tradeoff between size and the other benefits of an OLED screen.  A simple way to measure is to take a regular 8.5×11 inch paper as a convenient 11″ ruler.  This is not to say that the screen is a make or break proposition as there are far more other factors to consider, and I believe that the iPhone 4 the best overall phone as of June 2010.  But consumers should understand what high PPI actually means and a more informed consumer is a happier one.

Update 6/10/2010 - Analyst Raymond Soneira came to a conclusion that the PPI resolution falls short of the human Retina.

“So, if you hold an iPhone at the typical 12 inches from your eyes that works out to 477 pixels per inch,” Soneira added. “At 8 inches it’s 716 ppi. You have to hold it out 18 inches before it falls to 318 ppi.”

These comments makes absolutely no sense.  If he wasn’t misquoted (and I have to give Mark Hachman of PC Magazine the benefit of the doubt that Soneira was quoted correctly), then Soneira’s statement is completely opposite of what is true.  PPI or Pixels Per Inch stays the same regardless of distance held to the eyes but what does change is that angular resolution increases as you move the display away from the eyes so you don’t need as much PPI for a larger and more distant display.  This is why a 42″ 1080P HDTV only has 52 PPI and you can’t see any pixels on it because you’re sitting so far away.  Soneira is suggesting that the iPhone 4 looks worse and worse as you move it further away which is a baffling.  The correct conclusion is that the iPhone 4 overshot the PPI and not undershot.

42 Comments »

  • Ed said:

    Do you really need 300 PPI on a 3.5″ phone? Short answer = YES!

    I do some surfing and video watching in bed at night with my glasses off. I see every pixel on the screen, and sometimes it’s annoying. I can’t wait to see what the iPhone 4 looks like.

  • George Ou (author) said:

    @Ed, only if you put the phone within 13 inches of your eyes.

  • Tom said:

    Do you need 300 PPI on your business cards?

  • Robert David Graham said:

    The 300dpi is just a side effect.

    Apple needed a higher resolution to compete with other phones. Unfortunately, there is a huge library of apps that assume a 480×320 screen. The only way to make those apps continue to work is to precisely double the screen dimensions exactly to 960×640. Apple probably also wanted to keep the size the same. This resulted in 300dpi. Of course, now that they’ve overshot the mark, they want to convince everyone that they NEED that resolution.

    With that said, I suspect the difference will be still be noticeable when you put the iPhone side-by-side with other phones.

  • Nick Brown said:

    @Tom, That doesn’t work. You don’t use Pixels Per Inch on business cards. You use DPI or Dots Per Inch. Generally speaking 1 pixel would take 4 dots to mimic in printing.

    So in your question, “Do you need 300 [DPI] on your business cards?” Sure, you may. But that means the equivalent image could be produced on a screen with 75 PPI.

  • Brett Glass said:

    Those of us who are becoming presbyopic can’t read tiny print on a phone held that close anyway.

  • SAP said:

    Although you are right about the main physics of the resolution and what our eyes can see or not.
    However, there is a difference between static and dynamic. Due to the way we read and watch (etc.) our eyes do not rest in place constantly. Due to this “motion” (which also occurs because of holding a display not 100% steady) and due to our “CPU” (visual cortex) we actually are able to distinguish different resolutions even though they might exceed the actual resolution of our retina. (Main priciples of this are also applied in space telescopes on earth to improve resolution.)
    Therefore a “retian display” actually can be benificial.
    However, regarding the pure static physics, apple was untrue and you are right…

  • jake87 said:

    Your article kind of falls apart with everyone that has actually seen the phone claiming it DOES make a huge difference.

  • Justin said:

    @Nick Brown:

    It’s a reasonable comparison if you got your business cards done on a photo printer or if you have solid colours (the text should be solid).

  • MikeTek said:

    For what it’s worth, I do tend to hold my iPhone closer than 13 inches – more like 10.

    But I’m still on the first gen iPhone and have a hard time justifying the upgrade even with all the bells and whistles. It still craps on other smart phones IMO.

  • Serg3 said:

    From a certain point of view your article is technically correct, however, as you stated, making the screen over 252 PPI is pointless, it is only from the perception point. If you take in consideration manufacturing costs, it is way easier to manufacture double resolution (cuadruple for purists) screens than one that is only 1.35 times the resolution.

    Many manufacturing decisions are taken from different angles such as marketing, customer satisfaction, but also manufacturing economy

  • Paul said:

    You aren’t accounting for variance in holding distances. Assuming 300 at 11 is correct, you are assuming phones only held at 13 or more inches. The iPhone display makes pixels imperceivable beyond 10.1 inches and is an advantage at all distances closer than 13.

  • Ben said:

    As someone who has spent the last two decades annoyed at the absence of progress in screen resolution, I consider 326 a new standard, and anything less is outmoded. You wouldn’t consider a digital camera with less than 3 Mpx, but the best notebook screen is about 2.3, and most people put up with about 1 Mpx (XGA is only 0.8). Though I tolerate 110 ppi, I long for the day that computer screens don’t look like a bad fax. We gave up on 100 dpi printers 20 years ago, and most laser printers now do at least 1200 dpi. Supposedly we can’t see better than 300 dpi at typical viewing distance, but compare a 300 dpi print with 600 and you can certainly see the difference.

    For most of my 35 years of programming, I have been frustrated that I could see the individual screen pixels. I no longer can, without glasses, but I still want to be able to read subscripts and superscripts on 10 point fonts without zooming the screen, and have things look sharp without the anti-aliasing kludge. Of course, I would also like to read my 300 ppi screen in direct sunlight. I could do that with my PowerBook 180 (256-tone grey scale) in 1992, but unfortunately the move to colour put an end to that.

  • George Ou (author) said:

    @Ben

    “As someone who has spent the last two decades annoyed at the absence of progress in screen resolution, I consider 326 a new standard”

    No progress? 20 years ago we were doing 640×480 or less on most monitors using bulky 13″ to 16″ CRTs displays that cost $350 to $1000 which is equivalent to $567 to $1621 in 2009. Today we have 1920×1080 23″ LCD displays for $150 available to us. That’s your definition of no progress?

    Now it’s interesting you bring up digital camera sensors which eventually get blown up to full screen on a 20″ display. The iPhone 4 display is locked at 3.5″ and it’s typically viewed beyond 13 inches from the eyes which means a 3.7″ OLED display with 252 PPI will have a small size advantage and no visible disadvantage on PPI.

  • George Ou (author) said:

    @Robert,

    “With that said, I suspect the difference will be still be noticeable when you put the iPhone side-by-side with other phones.”

    It probably looks much better than most phones, but that wasn’t the comparison I was making. I was asking whether a 3.7″ or larger OLED display with 800×480 will look better than a 3.5″ 960×640 IPS display. I think that within 13 inches, the iPhone 4 will have the pixel density advantage but people may still prefer looking at a larger screen. The larger size has trade-offs obviously because it’s bigger and heavier and many people may not want to carry something that big.

    But held beyond 13″, the pixel density advantage becomes moot comparing 252 and 326 PPI and the size plays a much bigger role.

    Still, the only way to really test this is to take a photograph of two phones equidistant from the camera.

  • Justin said:

    A photo at 13″ isn’t going to prove anything since, ignoring the variability of cameras, a camera is not the same as the human eye. The only way to make a fair comparison is to see the screens in person, and that’s also going to vary.

    Obviously, people will prefer looking at a larger screen. But, as you mention, that’s not the only thing to take into account for a device designed to fit in a pocket. You can always make your screen bigger by holding it closer. You can’t make it more pocketable by holding it farther away. And the closer you hold it, the more you will benefit from a higher PPI.

  • Justin said:

    BTW, this distance thing is based on your casual observation. I know from my own experience that I vary the distance I hold my phone depending on what I’m doing. Sometimes it’s much more than 13″, sometimes less than 11″.

    One important thing here is not the screen size or the PPI, but how the app has been designed. The task app I use has large type, so I can easily see it at a distance. The Maps app is information dense, so I naturally hold it closer when I use it.

  • eloriane said:

    Why are you so dismissive of the idea that people might hold their phones closer than 13 inches?

    When I walk around campus with my phone, I hold it between waist-height and shoulder-height — which is 13 inches at the farthest. But I do most of my browsing in bed, when I first wake up, or when I can’t sleep– and that’s six inches away maximum!

    If it’s going to be clearer at viewing distances closer than 13 inches, for me that means it’s going to be clearer all the time.

    I might be an outlier here– but you might be, too. Stick to the tech specs without assuming everybody’s like you.

  • George Ou (author) said:

    @eloriane

    I never dismissed or assumed anything. What I said was that I don’t see many people holding their phone within 13 inches.

    If you hold your phone 6 inches from your eyes (which is generally the minimum focal distance of most people’s eyes, though it would be a bit of an eyestrain and would require noticeable crossing of the eyes), then you’re going to get a lot of benefit from the Retina Display.

    I have no reason to doubt what you are saying and I also said the iPhone 4 is the best phone ever produced, so it sounds like a perfect match for you.

  • Some noteworthy posts – June 9 2010 | Technology for Mortals said:

    [...] Do you really need 300 PPI on a 3.5 inch phone? Apple claims that 300 Pixels Per Inch (PPI) is the limit of the human eyes when viewing something approximately 11 inches away from the eyes, and that the iPhone’s 326 PPI beats competing Smartphones with only 252 PPI. 252 PPI is the eye’s limit at 13 inches, but do people really hold their phone less than 13 inches away? Categories: Apple Tags: Comments (0) Trackbacks (0) Leave a comment Trackback [...]

  • Sebastian Stephenson said:

    Interesting article however I have one question if you are an international reader and my question is what if you buy an ipad and you get the iPhone 4 which would have the sharper text or would there be little difference because the screen size and the distance you the hold two devices at? or because of the ipads 1024-by-768-pixel resolution at 132 pixels per inch or the iPhone 4 at 960-by-640-pixel resolution at 326 ppi?

    After reading your article again I the main differentator is the distance you hold the screen at and how big the screen is

    thank you for your reply

  • Sebastian Stephenson said:

    Interesting article however I have one question if you are an international reader and my question is what if you buy an ipad and you get the iPhone 4 which would have the sharper text or would there be little difference because the screen size and the distance you the hold two devices at? or because of the ipads 1024-by-768-pixel resolution at 132 pixels per inch or the iPhone 4 at 960-by-640-pixel resolution at 326 ppi?

    After reading your article again I think the main differentator is the distance you hold the screen at and how big the screen is. Am I correct so that it would make no difference?

    thank you for your reply

  • Marco said:

    I hold my iPhone closest (6-7″) when I’m using it to watch video content, read text or play games. All of these functions will eventually benefit from increased pixel density.

    It seems to me screen resolution was a war that Google started, not Apple.

  • SimonSays said:

    @George Ou & @Ben:

    I am sorry George, I like your article, but I agree with Ben on his statement: there is no progress in screen density.

    Sure, screens are becoming cheaper, but that’s not the point. The problem is that while screen’s resolution is increasing so does its total area.

    That means the PPI’s (pixels per inch) stay pretty much unchanged in the last 20years.

    In early 90s the state-of-the-art monitor was a 15-incher running @1024×768, that’s only 85PPI. Now the 30inch monitors boasting 2560×1600 resolution have only 101PPI.

    For more info see:
    http://en.wikipedia.org/wiki/List_of_displays_by_pixel_density
    http://en.wikipedia.org/wiki/List_of_common_resolutions

  • SimonSays said:

    @George Ou & @Ben:

    Ben wrote:

    As someone who has spent the last two decades annoyed at the absence of progress in screen resolution, I consider 326 a new standard, and anything less is outmoded.

    I am sorry George, I like your article, but I agree with Ben on his statement: there is no progress in screen density.

    Sure, screens are becoming cheaper, but that’s not the point. The problem is that while screen’s resolution is increasing so does its total area.

    That means the PPI’s (pixels per inch) stay pretty much unchanged in the last 20years.

    In early 90s the state-of-the-art monitor was a 15-incher running @1024×768, that’s only 85PPI. Now the 30inch monitors boasting 2560×1600 resolution have only 101PPI.

    For more info see:
    Wikipedia: List of displays by pixel density
    Wikipedia: List of common resolutions

  • George Ou (author) said:

    @SimonSays

    You just contradicted yourself. First you say there is no progress in screen density. Then you cite an example of progress from 85 PPI to 101 PPI. Furthermore, you failed to cite notebook PPIs and phone PPIs which are just as relevant as desktop displays. There are 15.4″ notebook screens with 1920×1200 resolution for example, and that blows away your 1990s example.

    But you missed the more important point. PPI is irrelevant to your eyes if the device is used at a greater distance. What is relevant is the pixels per degree (PPD) or the angular density. Human eyes have a theoretical angular density limit of 50 cycles per degree which corresponds to 100 PPD. The iPhone 4 has a PPD value of 125 at 11 inches which far exceeds the human eye which means it doesn’t have any kind of real advantage over a 252 PPI OLED display.

  • George Ou (author) said:

    @Sebastian Stephenson

    The PPI value is really irrelevant to the eyes because it all depends on distance. The more relevant metric is PPD. The iPad has a *much* lower PPI than the iPhone 4 but it looks more sharp because it has more pixels overall and you can sit back and watch it from a more comfortable distance. If PPI were all that mattered, no one would care about having a larger HDTV. But size does matter because you can sit further back and have more people in front of the HDTV within its sweet spot.

  • brisance said:

    Apple has doing a good job with assistive technologies in mobile devices, so having a higher pixel density would be useful if one were visually-impaired.

  • Justin said:

    Someone else has come to the opposite conclusion that you have using the same info.

    I’m still not convince either claim is accurate or relevant in real world use.

  • George Ou (author) said:

    @Justin,

    See my update in the post. That guy makes absolutely no sense in claiming that the Retina Display looks worse further away from the eyes.

  • SimonSays said:

    @George Ou
    It is nice to see, how passionate defender you are George, I truly appreciate it.

    In my statement above, I did not contradicted myself, I just simply assumed that average screen improvement of 1PPI per year is not worth a mention. I believed that the dear reader will do this simple math by him/her self, and come to the same conclusion that such minute improvement expresses rather an underachievement and not a progress.

    Yes I am certainly aware of higher PPI’s on notebooks’ screens as I type this comment on a 221PPI ultraportable. Besides, if I hadn’t been aware, I wouldn’t have appended links to Wikipedia, would I? To be honest I am a very happy with 221PPI. But that’s not a mainstream and neither 1920×1200 resolution on 15.4incher (147PPI) is.

    I wouldn’t say I have missed your point about PPD. I wanted to avoid mentioning it, so I could stay away from the pointless dispute whether 11inch or 13inch distance is the sweetest spot to use a device.

    Now that I feel invited into the PPD dispute I would like to point out that your math does not reflect that published by PCMag website.

    I cite PCMag, which on its turn cites Raymond Soneira, president of DisplayMate Technolgies:

    “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.
    So, if you hold an iPhone at the typical 12 inches from your eyes that works out to 477 pixels per inch, 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,” Soneira wrote. “It actually needs a resolution significantly higher than the retina in order to deliver an image that appears perfect to the retina.”

    Could you please comment on the above?

    Thank you in advance.

  • George Ou (author) said:

    @SimonSays

    As I pointed out, the PPI is far less irrelevant to how good something looks than the PPD value. This is why a 42″ 1080P HDTV has 52 PPI yet it has a higher PPD value than the iPhone 4 because of the distance involved.

    Furthermore, having a higher PPD is less relevant than the total pixel count. For example, does a 1920×1080 37″ 8-bit IPS HDTV look better or a 15.4″ 6-bit TN LCD with 1920×1200? The LCD has higher pixel count and it has a much higher PPI. However, the 37″ IPS HDTV can be moved to the desired viewing distance but most people would rather have it closer for online gaming.

    The point is that size matters because even if your Retina can handle a smaller display with higher pixel count, that doesn’t mean it’s an optimal viewing experience. People would much rather have the image fill a larger arc of view and make use of more sensor cones in their retina.

  • William R. Cousert said:

    If what Apple says is true (that 326 dpi is the maximum resolution a human retina can distinguish at 11 inches), why is it that output from a 1,000 DPI laser printer looks so much better than a 300 dpi laser printer?

  • George Ou (author) said:

    @ William Cousert

    Printers are not continuous tone devices. The dots are either all black or non-existent (white). To simulate shades of grey, they use patterns of black dots. To do this while maintaining the look of 300 DPI for grey scale images, you need 16 dots to simulate one grey “dot” and you need 1200 DPI to do that.

    For a continuous tone device like an LCD screen, 326×326 dots in one square inch is actually 978 RGB continuous tone elements.

  • Mark said:

    I realize that this article was published before anyone really got their hands on an iPhone 4, but I just have to say that even though the science differs from Apple’s claims, the result of their technology is simply spectacular. I have 20/20 vision last time I checked (about a week ago), and I can say with confidence that one can not differentiate between the pixels even from only a few inches away. I have never seen a higher resolution display in my life, and I can’t wait until this technology is available on a large display like a TV or a computer screen. Just think of how amazing that display would be. If Apple could fit 614,400 pixels in a small 3.5″ diagonal display, theoretically, they could produce a 56″ display with 157,286,400 pixels! Compared to a common 1080 display, this could have 10,240 horizontal lines!

  • Anonymous said:

    If you reread what you said about the quote…

    “So, if you hold an iPhone at the typical 12 inches from your eyes that works out to 477 pixels per inch,” Soneira added. “At 8 inches it’s 716 ppi. You have to hold it out 18 inches before it falls to 318 ppi.”

    These comments makes absolutely no sense. If he wasn’t misquoted (and I have to give Mark Hachman of PC Magazine the benefit of the doubt that Soneira was quoted correctly), then Soneira’s statement is completely opposite of what is true. PPI or Pixels Per Inch stays the same regardless of distance held to the eyes but what does change is that angular resolution increases as you move the display away from the eyes so you don’t need as much PPI for a larger and more distant display. This is why a 42″ 1080P HDTV only has 52 PPI and you can’t see any pixels on it because you’re sitting so far away. Soneira is suggesting that the iPhone 4 looks worse and worse as you move it further away which is a baffling. The correct conclusion is that the iPhone 4 overshot the PPI and not undershot.

    Soneira said the closer you hold the phone, the more DPI you need.
    You misread and said, that he said, farther away looks worse. Opposite way.

    Think about it. If you hold your finger at an arms length away, you cant see the fingerprint very well. Bring it within a few inches of your eye, and you can see it in immensely high detail. What Soneira said was right, and Apple needs to add more DPI if they want to make it more than the retina can process at 11 inches. The majority of people I know hold their phone about 8 inches away, so they need around 800 DPI, which is much more than the iPhone 4.

  • Anonymous said:

    If you reread what you said about the quote…

    “So, if you hold an iPhone at the typical 12 inches from your eyes that works out to 477 pixels per inch,” Soneira added. “At 8 inches it’s 716 ppi. You have to hold it out 18 inches before it falls to 318 ppi.”

    Soneira is suggesting that the iPhone 4 looks worse and worse as you move it further away which is a baffling. The correct conclusion is that the iPhone 4 overshot the PPI and not undershot.

    Soneira said the closer you hold the phone, the more DPI you need.
    You misread and said, that he said, farther away looks worse. Opposite way.

    Think about it. If you hold your finger at an arms length away, you cant see the fingerprint very well. Bring it within a few inches of your eye, and you can see it in immensely high detail. What Soneira said was right, and Apple needs to add more DPI if they want to make it more than the retina can process at 11 inches. The majority of people I know hold their phone about 8 inches away, so they need around 800 DPI, which is much more than the iPhone 4.

  • Anonymous said:

    Just wanted to add all this talk about 326 PPI @ 11 inches is the human eye’s resolution leaves out a major point. This is the limit of human resolution between black and white. Because most phone display do not produce pure white (ie. don’t have anywhere near a good contrast ratio (good being >1000:1), the actual resolution of the retina is quite a bit lower.

    Furthermore, there are several technologies that are not resolution-dependent to mitigate this type of effect.

    One of these technologies is very well known as anti-aliasing, which is implemented in Android-type devices (and probably Apple’s too although I have not read the specs on the iPhone)

    With my Evo’s 4.3 inch 800×480 display, I have the hold the phone something like 5 inches from my face to get some kind of blurriness and I have better than average vision — 20/15 in both eyes. This is to say, I can make out details in text at 20 feet, what normal people can only do in 15.

  • ravinder said:

    i know guys more pixel are better to view something on display…..but most of good phone have resultion 800*480 its mean ppi will be 233 for a 4inch display but also they are capable to play hd video which have resoultion 1280*720 or 1920*1080….. it mean they have ppi 386 or 852…………..how is it possible… according to mobile specification they are capable to show 233 pixel per inch but they are also playing hd video which have ppi more than double of its screen ppi……WHAT IS THIS

  • ravinder said:

    if i watch a hd video have resoultion 1920*1080 in my mobile which have screen 4 inch and 233ppi……..but the video ppi will be 852 according to mobile display size. will i able to see individual pixel if i watch hd video from a distance of 11inch……according to mobile specification its able to proces 233ppi but now its procsing 852ppi is it true.

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