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Apple Retina Display

By now it seems that most people on the planet have heard of Apple’s latest iPhone, the iPhone 4 which was released today.  One of the many compelling features of the new phone is the Retina Display.  When Steve Jobs first invoked this term at the WWDC, my eyebrows were raised.  Being a retinal scientist, I was immediately skeptical of just what he meant by “retinal display”.  My mind immediately raced and I wondered if it might have been some of the interesting technology I got to see on my last visit to one of Apple’s technology development labs.  I will not say anything about that visit, but this Retina Display, a super high resolution display was new technology that I had not seen before.  Essentially it is an LED backlit LCD display with a *326* pixel per inch (960×640) display (John Gruber of Daring Fireball called this resolution display back in March) where each pixel measures a scant 78μm.    Though as you can see from these images of the displays I captured under a microscope, these pixels are not square.  Rather they are rectangular and while the short axis is 78μm, the long axis on the iPhone 4 pixel is somewhere in the neighborhood of 102μm. Update 07/23/10:  After discussion with some folks, including an LCD engineer, they have pointed out that pixels are measured from center to center rather than edge to edge, so I have changed the scale bars to reflect new measurements with a micrometer. Additionally, others have emailed me noting that if the black space surrounding the pixels is taken into account, the pixels are in fact, square.  So, the measurement of 78μm for the iPhone 4 is in fact 78μm from center to center of every pixel.  Also, Ron Uebershaer sent in screenshots I’ve included at the bottom of this post that he made in MATLAB which conceptually demonstrate that the pixels are in fact square.

I am including images below of the iPhone 1G, the iPhone 3G, the iPhone 4G and the iPad to show some perspective on pixel sizes.  The scale bar and my measurements are approximate as I was having a tough time in the lab tonight finding an appropriate calibration.  Nevertheless, this should serve as a useful metric for examining the relative pixel sizes and for making the point of whether Apple’s Retina Display is marketing speak and hyperbole or if in fact, Apple’s claims have merit.

 

As you can see from this image, the iPhone 1G pixels (each composed of a red, green and blue sub-pixel) measure approximately 150μm x 500μm.  Also note the blurryness of the image.  This was optimally focused, but the LCD panel itself is behind a non-bonded pane of glass with touch sensor on it leading to some image degradation.

 

As in the 1G iPhone, the iPhone 3G pixels are essentially the same size, though with a different contact location.  Again, these pixels measure approximately 150μm x 150μm and this LCD display has the same blurring issues that are present in the iPhone 1G.

 

This image of the iPhone 4G LCD is made at the same magnification as the 1G and 3G iPhones illustrating the substantially smaller pixel size in the iPhone 4G.  These pixels are remarkably small and if you look carefully, appear to be composites themselves where each sub-pixel is composed of its own sub-pixels.  I am not sure about this however and it may simply be an artifact of the construction.  Also note that there is very little distortion in the pixel images as the iPhone 4G has a bonded glass cover, eliminating the space in between the LCD panel and the touch sensitive glass surface.

iPhone1: ~150 x 150μm

iPhone 3G: ~150μm x 150μm

iPhone 4G: ~78μm x 78μm

So… the claim from Steve was that this display had pixels that matched the resolution display of the human retina.  Now, fan of Apple that I am, this struck me as perhaps a bit hyperbolic, so I figured I’d do some quick calculations to see where this claim fell.  Apparently I am not the first Ph.D. to wonder as another came out calling the bluff of Mr. Jobs.  Here is the deal though… While Dr. Soneira was partially correct with respect to the retina, Apple’s Retina Display adequately represents the resolution at which images fall upon our retina.

Essentially, this is a claim of visual acuity which is the ability of the visual system to resolve fine detail.  There are an awful lot of considerations to take into account when making such a claim such as contrast, distance, the resolution of the display and some metric of pixel size which gives you an estimate of visual resolution on the retina.  Claims of contrast ratios are notoriously flexible in a number of displays and will be influenced by a number of optical factors as well as the content being viewed and the black and color levels of the pixels as well as overall luminance.  Apple claims an 800:1 pixel ratio and I’ll take them at their word on that and focus on the claims of resolution here.

A “normal” human eye is considered to have standard visual acuity or 20/20 vision.  This means that a 20/20 eye can discriminate two lines or two pixels separated by 1 arcminute (1/60 degree).

The ability of an optical system to resolve fine detail requires minute spacing of optical detectors.  In the retina, there detectors are the photoreceptors.  Objects we look at at projected through the cornea and lens and imaged on the back of the eye on a plane that ideally lines up with the retinal photoreceptors.

Theoretically the limit of retinal resolution, say the ability to distinguish patterns of alternating black and white lines is approximately 120pixels/degree in an optimal, healthy eye with no optical abnormalities.  Again, this corresponds to one minute of arc or 0.000291 radians (π/(60*180)).  If one assumes that the nominal focal length of the eye is approximately 16mm, an optimal distance from the eye for viewing detail might be around 12 inches away from the eye which is reasonable to assume for someone viewing detail on their iPhone.

Dr. Soneira’s claims are based upon a retinal calculation of .5 arcminutes which to my reading of the literature is too low.  According to a relatively recent, but authoritative study of photoreceptor density in the human retina (Curcio, C.A., K.R. Sloan, R.E. Kalina and A.E. Hendrickson 1990 Human photoreceptor topography. J. Comp. Neurol. 292:497-523.), peak cone density in the human averages 199,000 cones/mm2 with a range of 100,000 to 324,000.  Dr. Curcio et. al. calculated 77 cycles/degree or .78 arcminutes/cycle of *retinal* resolution.  However, this does not take into account the optics of the system which degrade image quality somewhat giving a commonly accepted resolution of 1 arcminute/cycle.  So, if a normal human eye can discriminate two points separated by 1 arcminute/cycle at a distance of a foot, we should be able to discriminate two points 89 micrometers apart which would work out to about 287 pixels per inch.  Since the iPhone 4G display is comfortably higher than that measure at 326 pixels per inch, I’d find Apple’s claims stand up to what the human eye can perceive.

 

For reference, I am also including an image of the iPad LCD taken at the same magnification as the iPhone images above.  As you can see, the pixel size is actually much larger and herringbone shaped which is not uncommon in high quality desktop displays like say, the Apple Cinema Display line.

 

 

Update 03/02/11:  Carles Mitjá has an entry with a proceedings citation highlighting image quality expectancy here.  He has three beautiful images of a MacBook Pro 15″ display, an iPhone 4 display and a very interesting 24″ Apple Cinema Display.

Update 08/24/12:  Looks like this article has resulted in my being quoted in the NYTimes for an article on choosing computer displays.

Update 12/15/13: Linked from an NBC News article on 4k televisions, Enough pixels already! TVs, tablets, phones surpass limits of human vision, experts say.

 

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  2. [...] Apple Retina Display – Jonesblog [...]

  3. [...] the com­plete cal­cu­la­tion take a look at Jonesblog’s Apple Retina Display arti­cle. And here’s what I con­cluded in Retina Display I wrote back on June 9th: So when [...]

  4. [...] as diferenças entra as telas do primeiro modelo do iPhone, do iPhone 3G, do iPad e do iPhone 4. Ele diz em seu blog que a tela do iPhone parece ser “mais confortável” para o olho humano do que a medida [...]

  5. [...] vas zanima naučno-tehnička strana priče, tekst Bryana Jonesa je pre­pun deta­lja i raču­na­nja da vas glava zaboli. Ili [...]

  6. [...] wel eens bevestigd zien dat het Retina Display van de iPhone 4 daadwerkelijk kleinere pixels heeft dan het menselijk oog kan waarnemen. Hij legde het toestel onder de microscoop en constateerde rechthoekige pixels van 78 x 102 [...]

  7. [...] Apple Retina Display – Jonesblog – (tags: apple retina display iphone4 science analysis optics lcd pixel ) [...]

  8. [...] behauptet, die Pixel-Unterscheidungsfähigkeit des menschlichen Auges übersteigt, sei mal dahingestellt. Fakt ist aber, dass die Auflösung von 960 x 640 Pixel bei 326 dpi schon sehr beeindruckende [...]

  9. [...] “”I’d find Apple’s claims stand up to what the human eye can perceive,” writes Bryan Jones after an exhaustive analysis of the iPhone 4′s 3.5-inch, 960×640 display. Article [...]

  10. [...] screen I’ve always wanted but never thought I’d see. It’s not just the pixel den­sity (which accord­ing to an actual reti­nal sci­en­tist, actu­ally does live up to the hype, even under a micro­scope), but what that pixel den­sity [...]

  11. [...] mostramos até agora devem ter sido insatisfatórias. Bem, agora não tem muito pra onde correr: um cientista usou uma aproximação que permitiu ver até os subpixels dos subpixels dos pixels na tela de um iPhone 4 (se é que [...]

  12. [...] Leia todo o artigo do Dr. Brian Jones aqui. [...]

  13. [...] (Bryan Jones), спeциaлизирующийся нa изучeнии сeтчaтки глaзa, oпубликoвaл рeзультaты сoбствeннoгo исслeдoвaния, кoтoрыe oпрoвeргaют [...]

  14. [...] screen I’ve always wanted but never thought I’d see. It’s not just the pixel density (which according to an actual retinal scien­tist, actually does live up to the hype, even under a micro scope), but what that pixel den­sity does [...]

  15. [...] The Apple Retina Display Under the Microscope – If you haven’t seen a ‘Retina’ display in person, these photos of iPhone [...]

  16. [...] (via prometheus.med.utah.edu/~bwjones/2010/06/apple-retina-display/) [...]

  17. [...] like with a resolution like that (or if we’d even tell the difference, given that our eyes have a limit on the amount of detail they can discern). Obviously, this is strictly a research project at this point — creating all of the [...]

  18. [...] like with a resolution like that (or if we’d even tell the difference, given that our eyes have a limit on the amount of detail they can discern). Obviously, this is strictly a research project at this point — creating all of the [...]

  19. [...] look like with a resolution like that (or if we'd even tell the difference, given that our eyes have a limit on the amount of detail they can discern). Obviously, this is strictly a research project at this point — creating all of the [...]

  20. [...] like with a resolution like that (or if we’d even tell the difference, given that our eyes have a limit on the amount of detail they can discern). Obviously, this is strictly a research project at this point — creating all of the [...]

  21. [...] look like with a resolution like that (or if we'd even tell the difference, given that our eyes have a limit on the amount of detail they can discern). Obviously, this is strictly a research project at this point — creating all of the [...]

  22. [...] es suficientemente pequeña para que el ojo humano no pueda distinguirlos (afirmaciones basadas en el artículo sobre el tema del especialista en Neurobiología de la Retina de la Universidad de Utah, el Dr. [...]

  23. [...] really improve on something like the Retina Display, which is supposed to have a pixel density that goes beyond what our eyes can pick [...]

  24. [...] like with a resolution like that (or if we’d even tell the difference, given that our eyes have a limit on the amount of detail they can discern). Obviously, this is strictly a research project at this point — creating all of the [...]

  25. [...] gráfico, olhei apenas a comparação de imagem dos modelos antigos para o novo iPhone: Fonte : Apple Retina Display. No site onde encontrei esta foto vocês também encontram detalhes técnicos.. Se alguém tiver [...]

  26. [...] Formally and technically these screens vary – in size and aspect ratio, display technology, spatiotemporal limits, and so on. They are united however in two basic attributes, which are something like the contract of the screen. First, the screen operates as a mediating substrate for its content – the screen itself recedes in favor of its hosted image. The screen is self-effacing (though never of course absent or invisible). This tendency is clearly evident in screen design and technology; we prize screens that are slight and bright – those that best make themselves disappear. Apple’s “Retina” display technology claims to have passed an important perceptual threshold of self-effacement, attaining a spatial density so high that individual pixels are indistinguishable to the naked eye (below – image Bryan Jones). [...]

  27. [...] за дисплейте на iPhone 4 е така наречения от Стив Джопс Retina display. AMOLED са по- добри от обикновенните LCD [...]

  28. [...] med sin Retina Display har högre upplösning än ögat kan urskilja. En klart intressant utredning som mynnar ut i följande.So, if a normal human eye can discriminate two points separated by 1 [...]

  29. [...] is a low traffic site with only about 250,000 unique visitors/year with posts that generate occasional spikes of insane levels of traffic, but the visitors are steady from almost all parts of the globe brought primarily through Google. [...]

  30. [...] Jones, Ph.D, retinal neuroscientist at the University of Utah, the eye is only capable of seeing 287 ppi. Note that this is based on the average human eye. Some people might have more sensitive eyes and [...]

  31. [...] Radians (อ้างอิง: Jones Blog) หรือที่บางคนเรียกว่า 1′ [...]

  32. [...] that nobody has made any quantitative imagery of the new iPad display yet.  So, in the spirit of the previous Retina Display post back when Apple first announced a “Retina Display”, I grabbed a couple of quick images on the microscope this afternoon.  The first image is from the [...]

  33. [...] have the effect of being unable to resolve individual pixels. With the Retina display however, you can’t distinguish between individual pixels, and so the image quality is essentially [...]

  34. [...] cierto, el dpi (puntos por pulgada) máximo de los ojos es aprox. 287 pixeles por pulgada, osea, menos que los impresos (300dpi) y menos que los celulares [...]

  35. [...] but the last time Steve Jobs invoked the Retina Display moniker, the vision scientist in me checked to see if his claims held up and sure enough, they did.  This time I was not so concerned withthe technical details of Apple‘s marketing claims, [...]

  36. [...] but the last time Steve Jobs invoked the Retina Display moniker, the vision scientist in me checked to see if his claims held up and sure enough, they did.  This time I was not so concerned withthe technical details of Apple‘s marketing claims, but [...]

  37. [...] en iPhone 4 med den på en nya iPhone 5, och även om skilnaderna är långt ifrån lika stora som mellan iPhone 3GS och iPhone 4 är det ändå en hel del intressant som kommer fram i hans [...]

  38. [...] with Apple’s Retina Display claim. He comprehensively explained his take on the matter on his blog and pointed out that “Soneira’s claims are based upon a retinal calculation that is too low”. [...]

  39. [...] mentioned the work of Bryan Jones, Ph.D and retinal neuroscientist at the University of Utah. He investigated and evaluated Apple’s claim that the new iPhones and iPad are Retina Displays and found those claims to be accurate. At a viewing distance of approximately 15-18 inches, which [...]

  40. [...] la del iPhone 5, aún cuando no tenga un nombre tan marketinero. Pueden leer mas sobre el tema en éste articulo, el cual habla sobre la densidad de píxeles que es capaz de percibir el ojo humano. [...]

  41. [...] Display (JDI) y Sharp. Como ya hemos comentado alguna vez en este blog, los estudios indican que el ojo humano sin entrenar no distingue más de 300 ppp, por lo que este incremento de densidad va más allá de lo razonable y, en nuestra opinión, [...]

  42. [...] bien, dado que el ojo humano sin entrenar no parecer ser capaz de distinguir por encima de 287 ppp, la tendencia actual de dotar a las pantallas de densidades de píxeles muy por encima de 300 ppp [...]

  43. [...] de píxeles tan brutal (y en cierto modo absurda) como 469 ppp. Para que os hagáis una idea, el ojo humano sin entrenar no parecer ser capaz de distinguir por encima de 287 ppp, por lo que todo lo que pase de 300 ppp resulta ser más un reclamo publicitario que una [...]

  44. [...] bien, dado que el ojo humano sin entrenar no parecer ser capaz de distinguir por encima de 287 ppp, la tendencia actual de dotar a las pantallas de densidades de píxeles muy por encima de 300 ppp [...]

  45. [...] Nada menos que una densidad de 538 ppp… y eso que decíamos que el ojo humano no distingue por encima de 300 ppp. [...]

  46. […] ya hemos comentado alguna vez, el ojo humano sin entrenar no parecer ser capaz de distinguir por encima de 287 ppp, por lo que densidades de píxeles muy por encima de 300 ppp resultan ser más un reclamo […]

  47. […] under normal usage. You can probably see pixels if you squint really close, but is there any real benefit to going up this […]

  48. […] here). As explained by someone much smarter than me (scientist and photographer Bryan Jones) in this article, Apple essentially topped what the average human eye is capable of distinguishing on a smartphone […]

  49. […] Samsungがもう一つ口を滑らしたのは、二年後の、スマートフォンのディスプレイの解像度の大幅増大だ。まず、来年はWQHD(2560 x 1440)のディスプレイを出す。そして2015年には3840 x 2106(Ultra HDとも呼ばれる)を出す。すばらしいことのように聞こえるが、でもわずか5インチの画面だ(fonbletはそれよりやや大きいか)。ぼくよりも頭の良い人(科学者で写真家のBryan Jones)がこの記事で説明しているが、平均的な人間が通常の使用距離で個々の画素を見分ける能力の限界に、すでにApple製品は到達しており、それはiPhone 4の326ppiのレティナディスプレイである。 […]

  50. […] primero en ofrecer una pantalla Retina) tiene una densidad en pantalla de 326 pixeles por pulgada. Acá tienen una explicación técnica sobre el porqué arriba de ese número (por encima de los 300 ppp, digamos) el ojo normal no llega […]

  51. […] having displays that go past the 342 ppi level or the 720p resolution on a 4.3” screen. Even the Retina display of the iPhones, at 326 ppi, is already sharp enough to be more than pleasant. Past these pixel […]

  52. […] which is equal to 300 PPI, and it is ok. But let’s check PPI value of 4.7” Full HD smartphones. In this case it equals 468 PPI, which is simply ridiculous. In most cases, 300ppi or so exceeds what the human eyes can readily […]

  53. […] que el ojo humano sin entrenar no parecer ser capaz de distinguir por encima de 287 ppp, la tendencia actual de dotar a las pantallas de densidades de píxeles muy por encima de 300 ppp […]