It is no secret any more that the display in the new Galaxy S4 is configured a bit differently and has been given the nomenclature of Diamond Pixel by Samsung, but as Bogdon Petravan  pointed out in his comprehensive article, the diamond shape refers to the subpixels.  (http://www.androidauthority.com/author/bogdan/ )  The pattern is actually much like the pattern in the Galaxy S3 in that is uses subpixel rendering and PenTile type algorithms to achieve the resolution.  The diamond shape is Samsung’s innovation further improves the fill factor and is useful in their drive toward still higher resolution OLEDs.  As you can see in this photo that Ray Soneira of DisplayMate obtained from Samsung, there remains a difference in the suppixel area of the red green and blue subpixels that correlates to the relative efficiency of each of the OLED materials. (http://www.displaymate.com/Galaxy_S4_ShootOut_1.htm)

There are as many green subpixels as there would be for the legacy RGB stripe configuration, but there are half as many red and blue subpixels.  Thanks to subpixel rendering there are just as many pixels as for the RGB stripe displays with 2/3s the number of dots.  At the resolution of 441 pixels/inch reviewers no longer able to see any issues with text clarity even for the most challenging fonts such as red on black.

Diamond PenTile Layout micrograph from Samsung via Ray Soneira

Friends and colleagues have heard me repeat an old expression, “ There is no such thing as being too thin or too rich.”  When it comes to displays it seems that there is a similar thing that can be said that a display cannot be too thin or too high in resolution.  In point of fact there are people who are too thin and there are limits to how much resolution can be seen.  But, we are not at that top end resolution yet.  My prediction is that the march toward increasingly higher resolution will end only when we get to 600 PPI.  The reason for this is that there are people who can focus (accommodate) a display at very close distances and can also resolve 50 cycles/degree.  Consequently, there will be some people who can still perceive pattern visibility.  At 440 PPI the PenTile OLED in the Galaxy S4 has exceeded the ability to see pattern visibility for all but those very few people with better than average accommodation and visual acuity.

At 440PPI the only way to retain the brightness and lifetime of an OLED display is with PenTile technology.  Don’t get me wrong, Samsung has made great strides in pushing their resolution capability to higher levels for both RGB stripe OLED as well as for PenTile OLED.  There have been reports that this is a result of combining PHOLED for improved red and green efficiency and OLED technology for blue (bit.ly/X51DsE).  Such a technique would allow for red and green subpixels to occupy still smaller percentages of the display real estate.  If a 440 PPI PenTile OLED is possible, then, by definition, an RGB stripe at 293 PPI is also possible.  That said, even for a 293 PPI display if one uses PenTile technology one can push up the brightness to improve outdoor viewability—a better choice for most users.

One blog today (http://bit.ly/15cQhWP  ) quoted me as saying that there is no technical solution for replacing PenTile in OLED smartphone displays on the horizon.  This is due to the inherent weakness in blue OLED materials, as confirmed to me by Professor Ching Tang, the inventor of OLED technology.  He said that the energetics involved in blue quantum excitation was at just at the right level to break the bonds in the OLED materials which means that there’s no solution in the forseeable future for improved blue OLED efficiency.

Can OLED displays extend beyond 440 PPI?  Only time will tell.

Galaxy S3 beats iPhone5 for best device of 2012 according to Lindsey Turrentine of CNET.

http://cnet.co/YWpaBX

After reviewing  the 10 best and most influential tech products of the year CNET found the Galaxy S3 as the leader and “worldwide hero”.  She specifically cited the large, vibrant HD display as a key attribute.  This phone uses a 300PPI HD PenTile RGBG OLED display.

Hill started out as a newspaper writer for 20 years in Scotland. In 1986 he joined Aldus to work on the development of their PageMaker layout program. He moved on to work at  Microsoft in 1994 to run its typography group and left Microsoft in 2009 to work on screen-reading projects. He died last Wednesday of a sudden heart attack.  He will be most remembered for his contributions in the development of ClearType, the application of subpixel rendering to the display of fonts.  It is difficult to imagine anyone who has not had the use of ClearType in today’s world.

Without question Bill Hill will be one of those people who so many will miss.

Bayer color filter pattern

Today this layout is universally used in all digital still cameras and smartphone cameras to enable ultra-compact cameras to capture images that are far better than would have otherwise been possible.  We owe Bryce Bayer an enormous debt of gratitude for his fundamental inventions in digital imaging and digital photography.  No doubt he will be missed by many.

Hi Joel,

I could not find a way to leave comments on the PenTile blog site, so I am emailing you instead.

I went to a Verizon store recently to look for a good replacement for my old Droid, and the widespread adoption of PenTile displays is significantly reducing my options.  The contrast, brightness, and saturation of Super AMOLED displays is excellent, and to my eyes they look superior to LCDs from a distance of a few feet or more, but held close enough to read, the PenTile checkerboard pattern is very apparent and distracting, especially at ppis in the mid 200s.  It’s less perceptible at 300-330 ppi in the latest applications, but still noticeable enough that I wouldn’t want to own one.

I understand the principle of the PenTile sub-pixel arrangement and sub-pixel rendering (which can also be applied to RGB stripes or other patterns), and find it very interesting.  However, there’s just no getting around what PenTile actually looks like to people with sharp eyesight.  It makes text, lines, and edges look fuzzy, and solid areas (other than green which is on every pixel) look visibly grainy.  For PenTile to look as crisp and smooth to my eyes as an LCD retina display at 326 ppi, it would probably have to be at least 400 ppi, maybe 450.  Once PenTile displays are in that range and I can no longer see the ugly artifacts, I will have no complaints with them.  Until then people with sharp eyesight like mine will continue to hate them no matter how good the contrast, brightness, and saturation.

For people who just don’t get it, and think PenTile displays look fine, try reading small text and looking at colorful and detailed pictures and icons on one through a powerful magnifying glass for a while.  That’s what it looks like to some people all the time!  Then do the same with an LCD, and even if you can see the sub-pixel pattern it doesn’t look nearly as annoying.  In fact, I would take a full RGB display over a PenTile display with the same number of sub-pixels any day, even though the ppi would be almost 20% lower and the brightness would be somewhat lower.  I can’t wait until Super AMOLED Plus (full RGB AMOLED) or 400+ ppi PenTile displays become mainstream.

Thanks,

- Dave

________

And my reply to Dave:

Hi Dave,

Thanks for your note.  I am sorry to hear that you had difficulty leaving a comment on the blog site.  I will look into why that might be.

First of all let me say that I am sorry to hear that PenTile displays are so bothersome to you.  I have no doubts that there are people like yourself who can resolve as high as 50-60 cycles/degree.  For people like yourself there is no doubt that the pattern visibility of PenTile is more apparent and can be bothersome. 

Looking at the chart you can see that normal vision is nowhere this good.  Sensitivity to luminance contrast modulation for normal human vision falls off significantly at 25 cycles/degree.  The ability to resolve chroma is far less as you can see in the 2D version of the plot to the right.

3D Plot of Human Vision System
Luminance Contrast vs Spatial Freq

Nouvoyance has never recommended the use of PenTile for 200 PPI smartphone designs.  In my opinion even a 4” WVGA at 233 PPI is stretching the application of PenTile a bit far, but even that is 24 cy/deg if viewed at 30 cm.  As you can see in the chart the cycles/degree is determined by first stating what your normal viewing distance is for a device.  For example, people rarely complain about TVs which have horribly coarse patterns, because they do not use them up close. 

Perhaps your ability to resolve high cycles per degree is not as much the issue as your ability to look at your phone from an incredibly short distance.  The ability to

Cycles/Degree by Application

accommodate at such short distances can be both a blessing an a curse.  If you can focus on a display from 10 cm could also easily explain why you see these patterns so readily.  Do you, for example, also see the pattern easily on the Galaxy SII which is an RGB stripe OLED?  It is no finer pitch for subpixels than PenTile.  If you see it, but find it less bothersome, this means that you have learned to adapt to that pattern and have not been able to do so for the PenTile pattern.  In the transition from CRTs to RGB stripe LCDs there were many people who had considerable difficulty in adapting to the visibility of the “jailbars”, but, over time, most people have benefited from visual adaption and were able to separate out the image information from the pattern.  Similarly, most people are not trouble by looking through window screens despite their intrusion on visibility. While I have never personally met anyone who could see the PenTile pattern in the Galaxy S3 at ~300PPI, I never doubted that such people like yourself existed.

There are also people who have the ability to see flicker better than most of the population.  They have a horrible time with the field sequential nature of TI based projectors.  They, too, have had to look at projectors in conference rooms that drive them nuts in a market where the technology was proliferating.

So let me give you the bad news first.  There is no technical solution for replacing PenTile in OLED smartphone displays on the horizon.  The highest pitch that has been recently demonstrated is ~260PPI which will go into the Galaxy Note II.  Beyond that, the OLED display industry must use PenTile to maintain a reasonble lifetime and brightness for the blue subpixels.  I had the occasion to chat with Professor Tang, the co-inventor of  OLED technology two weekends ago when he spoke at the 50^th Anniversary of SID.  I asked him if the lifetime issue for blue OLED material was fundamental, or if there is a good solution on the horizon.  He explained to me that the energetics involved in blue quantum excitation was at just the right level to break the bonds in the OLED materials.  He doesn’t see a solution in the forseeable future.  For this reason, I predict that you will continue to see many PenTile displays in OLED phones.    Furthermore, we are now seeing critical issues with battery life for tablets, so the ability to cut power consumption in half with PenTile RGBW LCDs will soon bring more PenTile LCDs to the market, starting with WQXGA formats of ~300PPI.  Most people will be delighted, but you, no doubt, will not.

Now for the good news.  There are already LCD alternatives available at your local phone provider for smartphones usng LTPS, and perhaps soon IGZO based backplanes that will give decent performance at 300 PPI.  These may not have the color gamut or response speed of the curent AMOLEDs, but they will be less troublesome for your vision.  The other good news is that the trend for increased resolution continues.  We will be seeing displays continue to 400PPI and 450PPI before too long.  I am guessing that even your vision will not be troubled by PenTile technology when we get there and you may even appreciate the improvements to power efficiency and/or brightness that PenTile technology will bring to LCDs.

Thanks again for your feedback.

Joel

PS:  Perhaps you would be willing to share with me a specific image or test pattern that you find most objectionable on the PenTile panels you have seen.  The people in our R&D team are always looking at ways to continue to improve PenTile display performance.  We have already made a series of improvements, not all of which have made it yet into products, but sometimes knowing what customers really find to be problematic will enable us to put our efforts into more productive solutions for future designs.

While displays have come a long way they still do not look as good as paper.  Even though paper doesn’t emit one photon of light, nobody ever says that it doesn’t look bright enough or colorful enough or flexible enough or thin enough or low power enough or sufficiently viewable from all angles.  One has to wonder if in 50 years we will yet have a display with the attributes of paper.

I could never have imagined in those early years  that anyone would ever complain that a display was too colorful.  Yet, that is exactly the conclusion of Ray Soniera of DisplayMate.  http://bit.ly/PgmCFN  He says that the display in the Galaxy S3 is too colorful because it has a color gamut in excess of sRGB, a standard that was historically picked for studio monitors. The iPhone5 has an LCD that very closely matches sRGB, so presumably that make this better that the Galaxy S3 that has a gamut that is ~105% of 1953 NTSC

On the other hand, every TV showroom is filled with TVs that strive for 1953 NTSC color gamut, a gamut that is 41% larger than sRGB.  It was correctly noted by some bloggers that if one offered a TV with only sRGB consumers comparing TVs would be very unlikely to pick the sRGB model for their TV.  You need to be a judge of this attribute for yourself.  While sRGB has been the gamut standard for web content, smartphones are increasingly displaying video, where the standard has been NTSC.  There are those who now expect their smartphone to be able to display both video and web content with the color of the most demanding application.

At this link you can see a comparison of both NTSC and sRGB

http://bit.ly/WlChYr

When I have demonstrated my Galaxy S3, those people that I have polled have been very impressed with the color and the contrast.  None have said it has gaudy colors.

Ray also comments that the Galaxy S3 needs to be brighter.  On this point I might agree.  If you want to use the S3 in full sunlight it is difficult to compete with an LCD that is also partially transflective.  It takes considerable brightness to compete with the sun.  That said it is largely due to PenTile technology that the S3 display is as bright as it is.  Brightness correlates to current density.  Lifetime is affected by current density.  Thanks to PenTile which reduced current density, the S3 is still viewable in rather bright environments.

Neither the Galaxy S3 nor the iPhone 5 display are yet up to the standards of paper, but I must say that both of these displays have come a long way from where this industry began only 50 years ago.

http://www.androiddoes.net/breaking-news/galaxy-note-wins-display-industry-award-at-sid-2012/

Shown below is T K Lee of Samsung SMD accepting the award at SID’s awards luncheon event.

Here is a photo of the Galaxy Note Gold Award winner exhibit in the Samsung booth.

So if the world’s experts in displays, who also generated he first comprehensive standard for display metrology published May 31, 2012 have judged this PenTile display as the best how can it be that so many bloggers persist in finding fault with PenTile displays? It is time to recognize the impact that PenTile has had on the display industry and the quality that it offers.

Shown below is the Samsung SID booth.

Amongst the roughly 30+ displays that were shown this about one half of these were PenTile displays, including the PenTile Super AMOLED displays used in the Galaxy Note, the Galaxy Nexus, the Galaxy Prime, the Galaxy Nexus and the newly announced  Galaxy SIII smartphones.  Samsung also exhibited their line of mirrorless digital SLR cameras, each of which uses a 3-inch VGA PenTile OLED display.

Last year he was awarded the coveted Wolf Prize in chemistry.  I have to wonder if he ever imagined the impact his idea would have 30 years later.  Together with his colleague,  Steven Van Slyke, many patents were awarded for this technology.

Professor Ching Tang from Democrat and Chronicle

AMOLEDs have lifetime that is related to the current density used to drive the OLED material.  This is especially true for blue since blue has the lowest brightness for a given amount of current.  The other way to say this is that blue OLED material has lower luminous efficiency.  To maintain the same brightness with blue, OLED display designers have to drive it with more current per unit area.

So how does PenTile technology help Samsung to extend lifetime for high resolution panels?

This comes from the ability to use 2/3s the number of subpixels in PenTile OLED (Super AMOLED)  relative to RGB stripe OLED (Super AMOLED Plus).  Thanks to PenTile technology’s use of subpixels rendering it is possible to have the same number of pixels as the equivalent RGB stripe.  With only 2/3s the subpixels, one can make the ratio of driven subpixel area larger with a smaller overall percentage of space in between subpixels (better fill factor), as compared to RGB stripe – which is what gives rise to the improvement in current density for a given brightness,  which in turn leads to better lifetime.

For lower pixel pitch, such as was used in the Galaxy S Plus, the current density was relatively low due to the coarser pixel pitch so the lifetime was fine.  But, at the pixel density of the Galaxy Nexus or the Galaxy S III, PenTile is the way to go, at least until sometime in the future when significant strides are made in blue OLED material luminous efficiency.  As I have said before, PenTile is an enabler that make high resolution OLED practical for the product brightness and lifetimes specs that we all have come to demand.   This is why you have never seen any production OLED  of greater than 250 dpi without a PenTile configuration.  If the demand for ever increasing pixel pitch continues, PenTile will still be key even if blue luminous efficiency sees some level of enhancement.