All posts in About PenTile

Where Can I Learn More About PenTile Technology?

Book Cover:  Mobile DisplaysI occasionally get asked this question at conferences and symposisia. I always point to our website and this blog, of course, but oft times, my interlocutor is interested in a deeper, more technical understanding. For this, I can proudly point to chapter 12, “Image Reconstruction on Color Subpixelated Displays”, of Mobile Displays: Technologies and Applications of the SID / Wiley series. Although the book was published five years ago, it is very up to date still.  For the engineer or technologist interested in the theory and operation of PenTile displays, both OLED and RGBW, it is a very good place to start.

This chapter includes a background on the history and theory of subpixel rendering, optimization of color subpixel layouts for subpixel rendering, a simple method to generate subpixel rendering filters, RGBW color theory, Dynamic BackLight Control (DBLC, aka global or local dimming of the backlight to save power on RGBW LCD displays without compromsing image or color quality), and finally, the data processing pipeline used in all PenTile digital signal processing cores.  In writing this chapter, I viewed it as a basic primer on the technology, though of course, many details were left out by necessity in favor of brevity.

The book may be purchased at the Society for Information Display website bookstore.

Handing Off the PenTile Blog to Nouvoyance CEO – Candice Elliott

This blog will be my last as I hand this blog over to Candice Elliott, the founder of Clairvoyante and the principal inventor of the technology we refer to as PenTile.  PenTile technology has experienced a long and arduous evolution over which we have learned many important lessons.  Some have said that the technology was introduced too soon—business compelled us to introduce the technology into phones at 280 PPI and less, where some noticed pattern visibility.  Now that the standards have moved well beyond 300 PPI, to even 441 PPI for the Galaxy S4, there are few who can see any pattern visibility and are enjoying the benefits of PenTile technology.

Although Motorola and Nokia had developed phones based upon PenTile RGBW LCDs, PenTile LCDs have seen less adoption than has PenTile OLED.  However, now that resolution is creeping up for tablets to match that of phones, we again are seeing new opportunities to bring PenTile RGBW LCDs to the market to solve the battery life and brightness demands of tablets.  Samsung Display demonstrated at Display Week both the 10.1” WQXGA (2560 x 1600) “Green” display as well as the 13.3” 3200 x 1800.  Keep your eyes open for these in tablets this year.  The 10.1” WQXGA is already being used by one tablet provider in the USA and reviewers have noted the very long battery life that is spec’d.

Although I will be moving on to new challenges elsewhere, I remain a dedicated user of PenTile based products and foresee a continued path of adoption for PenTile technology as people continue to buy thinner, lighter and higher performance consumer electronics.  There is still no technical display solution that surpasses the benefits of PenTile for highly efficient, high resolution displays.

Cheers!

 

Joel Pollack

GAlaxy S4′s Diamond PenTile Display

Today I had my first chance to lay hands on the production version Galaxy S4 in an AT&T store.  My feeling was that it would be an incremental improvement over my Galaxy S3, but I was soon convinced that I would trade in my S3 in a heartbeat.  Not only was the HD screen able to display more information in crisp detail, but the phone gave me the impression of being smaller, thinner, lighter, brighter, and faster.

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

PenTile and Sharp Eyesight

Here is an email I received from someone who was unable to post his comment:

 

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 50th 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.

 

SID’s 50th Anniversary – Then & Now

This past weekend marked a milestone for the electronic display industry, the 50th anniversary of the Society for Information Display (SID) which was celebrated at its birthplace, Boelter Hall at UCLA.  SID is the preeminent organization serving the display industry, sponsoring symposiums for display technology and display business.  Several of those early contributors have passed away in recent years.  Looking back 50 years, the industry was still using Nixie tubes and was only developing commercial CRT displays.  I have a clear memory of my early days at Xerox R&D as a co-op student more than 40 years ago, asking my boss what the ideal display would look like.  With only a moment’s thought he pointed to a memo on his desk and said that it would look just like this – paper, but would be instantly reconfigurable.

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.

 

 

PenTile Super AMOLED Chosen for Display Application Gold Award – 2nd Year in a Row

There is one organization that is more focused than any other on displays—the Society for Information Displays, now celebrating its 50 year anniversary.  Display Week is held each year as a gathering of the world’s display experts.  After evaluating every new display component that has been introduced into products this past year SID selected the display in the Samsung Galaxy Note for the gold award winner.  You might recall that the display in the Samsung Galaxy S won this award last year.  So, for two years in a row a PenTile OLED panel has been awarded this coveted honor.

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.

Why PenTile Technology Improve OLED Lifetime

Many bloggers have picked up on comments that Philip Berne of Samsung made at a recent press event.  He explained that the reason that Samsung chose PenTile Super AMOLED over RGB stripe AMOLED was that of lifetime, specifically that of blue subpixels.  He is exactly right, but let me explain this a little more.

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.

Galaxy S3 Arrives — and, yes, with PenTile Super AMOLED

Samsung Galaxy S3

At long last the long awaited Galaxy SIII smartphone has emerged and the blogs such as Android Community  http://bit.ly/K5t9Rz are describing the unboxing.  Despite the many speculations about Samsung abandoning PenTile for this 720P OLED display  http://bit.ly/JFb79Z , it is now apparent that this didn’t happen.   http://engt.co/IpwdXs  Samsung has not abandoned PenTile and still counts on PenTile for such high resolution OLED displays such as the Galaxy S3 with a 306 PPI layout.

When bloggers refer to PenTile Super AMOLED as being cheaper, I have to ask them, “Cheaper than what?”  Show me a comparable, high resolution RGB stripe AMOLED display to compare this to.  If there is no such displays any discussion of relative cost is meaningless.  PenTile technology remains an enabler for high resolution OLED applications, not a cost reducer.  And, as long as the demand for ever increasing resolution continues you will see many more such PenTile OLED designs.

Increasingly I am seeing blogs that ask what is wrong with PenTile anyway.  Despite the vocal critics, at a pixel pitch in the range of 300ppi+  PenTile technology is a great fit for these applications.

Just Look for Yourself

While it seems fashionable to criticize PenTile technology, increasingly we are reading blogs that refer to PenTile displays as  “oft maligned” but “looks fine to me”.   The reality is that as PenTile technology has moved to the higher end of resolution >300 ppi it doesn’t look less than sharp.  One example was this recent post regarding the RGBW in the Nokia E6.  Most people do not even realize that this display is a PenTile LCD.

http://bit.ly/HrspZI

This author, who never specifically noted that this displays was PenTile technology,  commented:

“…But we have no issues with the crispness and the brightness of the display as it works well with 640 x 480 …”

It comes down to looking at PenTile displays for yourself and not being misled by any negative blogs or claims of fuzzy text.

Opportunity to Learn More About PenTile Technology

For those who would like more information about PenTile OLED and PenTile RGBW technologies for mobile products, you may wish to attend the up coming talk by Nouvoyance CEO Candice Brown Elliott in Southern California, “AMOLED vs. Hi-Res LCD for Premium Cell Phones”.  She will be speaking at the Los Angeles Society for Information Display Chapter’s annual symposium on “Emerging Display Technologies” on February 3rd, 2012.  For more information regarding attending the symposium, visit the LA SID Chapter website:  http://www.sid.org/ConferencesExhibits/LAChapterEmergingDisplayTechConference.aspx

 

Ms. Brown Elliott will also be speaking in Northern California, at Stanford University on the 28th of February on the topic of “Reducing Field Sequential Color Break-Up Artifacts using a Hybrid Display with Locally Desaturated Virtual Primaries”.  This talk will cover the development of the PenTile Hybrid Multi-Primary Field Sequential Color display that was demonstrated by Samsung in their DisplayWeek 2011 booth last May in Los Angeles.  For more information regarding attending the talk, visit the Stanford Center for Image Systems Engineering website:  http://scien.stanford.edu/