All posts tagged OLED

PenTile for Digital Still Cameras (DSC)

There was a very thorough review of the Samsung NX10 camera on dpreview which uses a 3.0-inch VGA PenTile RGBG OLED display.  This review covers every aspect of this camera including the display.

I would like to only make a couple of minor corrections to this reviewer’s comments.

1.  PenTile technology was not used for this camera display to save power.  OLED can be intrinsically low power if the user interface is design to be predominantly black with white or bright text or graphics.  OLEDs do not consume power where they are not being lit up.  Unlike smartphones where users are accessing any and all pages on the web, the for a DSC can be entirely designed by the manufacturer and can take maximum advantage of this property of OLEDs.

Instead PenTile technology is applied here to enable such high resolution while maintaining such good brightness and a display  lifetime equivalent to lower resolution displays.

2. The author says

The other difference is that, rather than using a red, a green and a blue triplet of dots to represent each pixel, it uses pairs of sub-pixels to present the same information, in a way that is claimed to be visually indistinguishable. This technology, originally developed by a Californian company, is now owned by Samsung. As explained in this white paper, the screen offers the same resolution in luminance terms as a conventional screen. What isn’t made quite so clear is that you don’t have full color information at each pixel (because you’ve effectively got 640×480 green sub-pixels and two offset 320×480 matrices of blue sub-pixels and red sub-pixels).

Nouvoyance never says that PenTile is visually indistinguishable. We do say that it is equivalent in resolution per the VESA spec offering the same resolution as an equivalent RGB stripe display.  The author then says we don’t have the full color information at each pixel.  This is not the case.  Subpixel rendering allows us to create luminance centers at every logical pixel on the screen in the full resolution–here at 640 by 480 VGA.  It is quite true that there are fewer red and blue subpixels than green, so the red and blue luminance information may be positioned slightly further from the center of the center of the pixel in some circumstances, but every pixel will have the correct and full luminance information.

The comment that PenTile doesn’t have full color information at each pixel is strictly speaking correct, but this has far less impact than those words convey.  There is full color resolution in the vertical and horizontal at every pixel, but there is a slight reduction in color information on the diagonal. It would not be possible to detect this for photographs.  For PenTile RGBG OLED there is a reduction in chrominance information on the diagonals, but it is not such a reduction that the human vision system (HVS) can detect this except for selective test patterns which would involve fully saturated red on black.  Keep in mind that the human vision system can resolve 50-60 cycles/degree of luminance information, but only 6 cycles/degree on the red/green line of colors and only 3 cycles/degree on the blue yellow line of colors.  For this reason the vision system cannot tell where each color subpixel is located relative to the logical pixel.  As an expert on cameras the author is probably familiar with how the camera sensor uses a Bayer pattern (see below) that functions in much the same way.   Similarly, JPEG compression uses the same difference in resolution of luminance and chrominance to achieve some portion of this compression.  In neither of these cases, do people claim that these implementations lack full color information.

Overall the review was excellent, but I wanted to set the record straight as to the purpose of PenTile OLED, what we claim for the merits, and what we achieve with this technology.

Comparing RGB Stripe Text to PenTile RGBW Text

My post showing the comparison of fonts with RGB stripe to PenTile RGBW LCD and PenTile RGBG OLED still left a few people confused, so I am going to illustrate this one more way.  Previously, I compared the results for the same number of columns.  Since PenTile RGBW can represent the amount of information in one-third fewer columns my prior blog showed the PenTile RGBW with one-third more font information.

This time I am comparing the same amount of font information, where PenTile RGBW used one third fewer columns, but have stretched the columns horizontally to match the horizontal space of the RGB stripe, just as it is done in products today.  This allows the comparison of equivalent size single stroke Arial fonts between RGB stripe and PenTile RGBW.

RGB Stripe (Top) - PenTile RGBW (bottom) As Rendered (left) - Blurred to Simulate Viewing Distance (right)

 

Perhaps you may wonder why there are some color subpixels turned on in places such as the vertical stroke of the “D”.  The reason is that if viewed at the normal distance, and if these subpixels were turned off, such a rendering would cause a color error to the white that was adjacent to the black line.  Rendering this as has been done prevents such color error at the edge of this font.  And, yes the PenTile RGBW should look brighter than the RGB stripe since this is a representation of the relative light transmission of PenTile RGBW vs RGB Stripe

The only problem is that this magnification is not at all how the human vision system sees this.  At the viewing distance for which this is design, that which you see will be blurred to hide the subpixels.  Move away from your screen until the subpixels on the lft hand images  are not apparent and you will see this as finished product would appear.

Moving away from the display has also be emulated by taking the images on the left and blurring it in Photoshop HSL space to create the images on the right that more accurately represent how the vision system sees these font renderings.

Perhaps you may wonder why there are some color subpixels turned on in places such as the vertical stroke of the “D”.  The reason is that if viewed at the normal distance, and if these subpixels were turned off, such a rendering would cause a color error to the white that was adjacent to the black line.  Rendering this as has been done prevents such color error at the edge of this font.

The only problem is that this magnification is not at all how the human vision system sees this.  At the viewing distance for which this is design, that which you see will be blurred to hide the subpixels.  Move away from your screen until the subpixels are not apparent and you will see this as finished product would appear.

Moving away from the display has also be emulated by taking the image on the left and blurring it in Photoshop HSL space to create the images on the right that more accurately represent how the vision system sees these font renderings.

PenTile RGBW – Why it has Higher Contrast

Recently, when showing the new WQXGA PenTile RGBW panel to editors I was asked if this was an OLED panel.  When I asked why she thought it was OLED she told me it was because the contrast was so high.  I decided then to generate a blog to explain why PenTile RGBW has such high contrast.

First let me say that OLED panels have the best indoor contrast of any displays.  This is simply because they only emit light where they are driven.  This leads to extraordinary blacks.  LCDs have a lower level of contrast than OLEDs unless one views them outside, where the reflective component of the LCD optics starts to have an impact.

PenTile RGBW, however, has contrast that is higher than other LCDs both inside and outside.  This is entirely due to the nature of light leakage in LCDs.  As it turns out, LCDs primarily have most of their light leakage near the perimeter of each subpixel.  This is a result of the way that an LCD is fabricated and driven.

If one compares RGB stripe to PenTile RGBW you can see that there is far less perimeter for the subpixels in a PenTile RGBW.  Keep in mind that in a PenTile RGBW that we have one-third fewer subpixels that an RGB stripe.  This changes the shape of each subpixel from a 3:1 aspect ratio to a 2:1 aspect ratio as is illustrated below.

RGB Stripe LCD Perimeter

 

 

 

 

Remember that PenTile only uses 2 subpixels per pixel on the average, compared to RGB stripe that used 3 subpixels per pixel.  When one calculates the relative amount of subpixel perimeter in the PenTile RGBW, and compares this to the RGB stripe, one finds that it has 28% less perimeter to leak light.  This directly leads to a comparable improvement in contrast ratio.

Illustrated below is roughly how this leakage would appear if viewed at high magnification.

RGB Stripe LCD Dark State Leakage

RGB Stripe LCD Dark State Leakage

So it is should come as no surprise that a PenTile RGBW LCD appear higher contrast than the comparable RGB stripe LCD.

Fonts – comparing RGB Stripe to PenTile

As promised, this blog will illustrate small fonts compared between RGB stripe LCD, PenTile RGBW LCD and PenTile RGBG .

In the comment from Khalid H. he said that Arabic fonts cannot be read on his HTC phone equipped with PenTile, implying that PenTile cannot render Arabic fonts.  Unfortunately, Khalid did not mention what font size or style of Arabic font, and there are so many. I borrowed a clipped section of an Arabic font from Middle East International Services (http://www.dalilusa.com/arabic_course/text01.asp). I displayed these fonts on my PenTile RGBW LCD and tried to photograph these incredibly small fonts.  Even with the best lens on a Canon SLR, I went beyond the resolution limits of this lens to get a sufficient focus.  So instead, display simulator tools were used to render these characters in RGB stripe, PenTile RGBW and PenTile RGBG as is used for OLED.

I have to agree that I could not read these on PenTile, but then I also could not read these on RGB Stripe, since I do not read Arabic.  Just the same, I am posting the comparison between RGB Stripe, PenTile RGBW and PenTile RGBG .  I compared  these using an eye loop to the actual fonts displayed on our PenTile and RGB stripe screens and the rendering is matched exactly.  As you can see below, the comparison speaks for itself.  PenTile RGBW and PenTile RGBG can render these tiny single stroke fonts equivalently to RGB stripe.  Even the white dot in in the small square is rendered perfectly, or at least it seems that way to a non Arabic reader, but in any case it too compares well to RGB stripe.

The relative brightness is a true representation of how PenTile RGBW will appear on a screen at comparable power.  In each case there are 600 pixels of width, but with PenTile we eliminate one-third of the subpixels, so 600 pixels includes more information than for RGB stripe.

RGB Stripe LCD

PenTile RGBW LCD

PenTile RGBG OLED

For good measure, I did the same exercise with an Arial, English letter font.  Ariel was chosen because there were good options for small single stroke fonts.  I cannot see any problem with how this is being rendered in PenTile.  While some may say that fewer subpixels should lead to fuzzy fonts, it simply is not true.

RGB Stripe LCD

PenTile RGBW LCD

PenTile RGBG OLED

These fonts are zoomed in to a level that one should never look at fonts.  Both PenTile and RGB stripe are looking rather jaggy.  That is true for both RGB stripe and PenTile displays.  Of course, large fonts that are not single stroke, especially when displayed on larger diagonal displays can look better than these small fonts, except that they too will also look more jaggy at the edges.  PenTile is never recommended for low dpi, not because it renders incorrectly, but because the pattern will become visible at lower dpi.

Note that I did not try to test these on phones or with specific types of software, because I don’t have access to the wide variety of phones that some bloggers seem to have.  There are variations in SW and other factors unrelated to PenTile that can make these images look different than the rendering engine is capable of producing.

 

________________

Update in response to the comment from Khalid H. last weekend.  He suggested that such disconnected fonts were not as difficult and suggested that we look at Arabic Droid fonts which are more connected.  With his help we downloaded this font and generated some text in similar size small fonts to what we used last time.  Then we  rendered these as RGB Stripe, PenTile RGBW and PenTile RGBG to enable a comparison between RGB stripe and PenTile LCD and PenTile OLED versions.  You can see this result below.  Khalid, I hope this is more convincing.

RGB Stripe LCD - Arabic Droid Font

PenTile RGBW LCD - Arabic Droid Font

PenTile RGBG OLED- Arabic Droid Font

Response to Tested Blog – A Review by W. Fenlon

On June 9th Wesley Fenlon posted an article at Tested “How PenTile Displays Are Brighter But Not Always Better.” This article was in some ways even more difficult to follow than the one we recently struggled to translate from Russian.  The biggest part of the confusion was between PenTile RGBG OLED and PenTile RGBW LCDs as well as the unrelated diversion into metal oxide backplane technology.

Let me begin by differentiating these two implementations of PenTile technology:

PenTile RGBG OLED

  • Value proposition:  enables OLED to achieve higher resolution with equivalent brightness
  • How accomplished:  eliminating one-third of the subpixels reallocates the dead space around each subpixel into useful luminous areas, reducing current density and allowing high resolution panels to appear as bright as lower resolution panels without lifetime degradation.
  • PenTile algorithms:  subpixel rendering SPR, edge sharpening

PenTile RGBW LCD

  • Value proposition:  improves transmissivity of the LCD
  • How accomplished:
  1. Adding a clear subpixel to pass white light from backlight without significant attenuation
  2. Eliminating one-third of the subpixels allows each subpixel to be one-third wider and have better aperture ratio
  3. Using dynamic backlight control (DBLC) allows images to be analyzed to add global dimming, to reduce power to the backlight , while preserving the color of high luminance saturated colors and at the same time increasing the contrast.
  • PenTile algorithms:  RGB to RGBW gamut mapping, subpixel rendering SPR, edge sharpening , image analysis for dynamic backlight control

Let me add another clarification:  RGB stripe can be used in both OLED and LCD.  PenTile can be used in both OLED and LCD.  Wesley confuses things by comparing a PenTile RGBW LCD to a RGB stripe OLED like the Samsung 4.5-inch Super AMOLED Plus

So Wesley had it right when he said that the PenTile RGBW used in the WQXGA panel had a fourth subpixel (clear or white) to let more light through, “making the screen brighter as it consumes less power”.  He also had it right when he said that”… backlight dimming for darker images, the 2560 x 1600 PenTile display clearly has an advantage in power efficiency…”

Wesley says that “PenTile screens have fewer subpixels overall than RGB (stripe) LCD arrays.  The pixels are also bigger, which means screens for these display(s) often have to be slightly larger than (RGB stripe) LCDs, hence that 4.5” Super AMOLED Plus on the Samsung Infuse…”   Let me correct and clarify this.  It is true that for a given diagonal size that the subpixels are larger, than the equivalent RGB stripe panel, however the pixels are equivalent.  PenTile displays use logical pixels that contain varying numbers of subpixels with luminance centers equivalent to an RGB stripe panel.  RGB stripe displays are comprised of pixels that each have 3 subpixels and are always the same size.  This is true for both LCD and OLED.  Having fewer and larger subpixels does not cause image quality issues that were supposedly illustrated with pictures in Wesley’s blog and have previously appeared in other blogs.  Shown below are images that I took myself from an RGB stripe display and from a PenTile RGBW display.  You will see that PenTile images with equivalent number of pixels (not subpixels) as RGB stripe do not suffer from blurriness or lack of crispness (note that some small amount of aliasing/moire on both images is due to the digital nature of such image capture). I did nothing in Photoshop to change the quality of either image other than equivalent scaling to fit the format needed for the blog.  In a future blog I will show such a comparison of B&W text to illustrate again that such text is not degraded by PenTile

 

My photo of a PenTile RGBW LCD

My photo of an RGB Stripe LCD

 

 

Samsung has offered WVGA 4.3-inch and 4.5-inch diagonal AMOLED.  These are RGB stripe LCDs.  Samsung offers WVGA AMOLED that are 4.1-inch and smaller that are PenTile OLED.  The reason that PenTile is not offered in these larger sizes is that it would exhibit pattern visibility at such a low dpi and offers less value to these OLED designs.  If however OLED were needed in high dpi at these larger diagonal sizes thenPenTile OLED would again have utility.

In the final paragraph of Wesley’s blog he states that “…the RGBW layout, (for) the 2560 x 1600 PenTile does seem to be employing that same improvement…”  I am not entirely clear which improvement he is referencing, but since it follows the reference to the Super AMOLED Plus, I think he means the use of RGB stripe.  It is true that the 2560 x 1600 panel does not use RGB stripe, but it also is not AMOLED.  The reason it does not use RGB stripe is that an amorphous silicon TFT backplane at 300 dpi with today’s state of the art technology would have about a 30% aperture ratio, making it impractical for power consumption for a table application.  Perhaps LTPS or metal oxide transitors might improve this aperture ratio, but uniformity of these technologies for 10.1-inch diagonal has yet to be demonstrated in production.  Once that technology is proven for this diagonal, it may allow practical tablet applications, but at that point PenTile technology could again be applied for an additional 40% improvement in power efficiency.  When comes to saving power, saving more power is always better.  I like to say that people are never too thin or too rich and likewise panels never save too much power.

One other small point is that this WQXGA demonstration panel already has a very wide viewing angle technology that is very similar in performance to IPS.  PenTile can be combined with any WVA technology for wide viewing angle performance equivalent to that seen on an RGB stripe panel.

To conclude

  • PenTile technology does not create blurry images or black and white text.
  • PenTile RGBW LCDs are more power efficient than any other technology in the market.
  • PenTile RGBW LCDs can be combined with IPS or any other wide viewing technology.
  • PenTile RGBW LCDs are fit for use on tablets due to the demands for high resolution and low power consumption.

Does PenTile Have Fuzzy Text?!

Some people claim this to be true based on what they expect they should see with fewer dots, but for typical black text on a white background, this is not the case.

Take a look at this recent post by Droid Life: http://bit.ly/jCgVLj

Black and white text used on PenTile is every bit as sharp as that used on an RGB stripe display – even for single stroke fonts. Evidence of this is shown in the image below – where the font is magnified to a size well beyond what’s used for normal viewing.

While the subpixels appear different than the RGB stripe, at normal viewing distance the fonts are indistinguishable between the two.

There are those who assume that this isn’t the case, as they do not understand the nature of subpixel rendering or PenTile’s edge sharpening filters. But photographs prove that this is the case!

The image featured below was published on Engadget and presumably showed that PenTile OLED text (on the left) was not as sharp as the SLCD stripe display (on the right) by enlarging it to a level beyond normal use.

Look closely at the single stroke letter “n” which is white on black font in the word “Calendar” and judge for yourself.

Didn’t Samsung Dump PenTile in Favor of RGB Stripe?

Not hardly!

At the end of February bloggers speculated about this in blogs such as:

http://www.displayblog.com/2011/02/22/samsung-super-amoled-plus-dumps-pentile-matrix-goes-real-stripe-rgb/

At CES 2011 Samsung introduced the new Galaxy S2  phone with a 4.3-inch wVGA RGB stripe OLED display that they refer to as Super AMOLED Plus. The horizontal subpixel dot pitch in this phone is about the same as that of the 3.1″ PenTile OLED panel introduced in products more than a year ago. There have been more than 70 mobile products that have been introduced with PenTile displays, most of then PenTile AMOLED. Many of these continue in production with PenTile OLED displays. PenTile technology remains very useful for the highest resolution AMOLED displays that are still being made.

At SID’s Display Week 2011 there was more than one new Samsung PenTile  LCD display technology being shown. New PenTile products continue to be developed by Samsung.

 

Award Winning PenTile Display

It seems that one of the displays using PenTile technology has received an award, the Silver Display of the Year Award (see below).  Actually the award was given to Samsung SMD who created the display for the Samsung Galaxy S that used innovative methods for combining an OLED display with an optically bonded capacitive touch panel that was a big part of the Galaxy S success.  Many bloggers have already noted that this display was PenTile RGBG.  For some time now Samsung SMD has been demonstrating  and selling displays using PenTile OLED in sizes of 3.1-inch, 3.3-inch, 3.5-inch, 3.7-inch,  4.0-inch and 4.1-inch.  It is great to know that the prestigious Society of Information Display has recognized the “exceptional display quality” of this design.

The press release on this year’s awards can be found here:

http://www.virtualpressoffice.com/publicsiteContentFileAccess?fileContentId=503685&fromOtherPageToDisableHistory=T&menuName=Events

 

Silver Award: Samsung Mobile Display On-cell Touch AMOLED

Samsung Mobile Display developed its OCTA – on-cell touch active-matrix light-emitting diode (AMOLED) – display to meet the ever-increasing performance and industrial design demands of today’s modern mobile devices. Unlike prior-generation touch-capable mobile displays, the OCTA display integrates the touch sensor onto the display itself, rather than fabricating the sensor on a separate glass substrate and then laminating it onto the display. This innovation, embodied in the OCTA’s projected capacitive touch detection technology, greatly reduces product weight and thickness, while increasing touch performance and response via the multi-sensor input capability that enables gesture recognition for the most advanced mobile devices. Moreover, because AMOLEDs are self-emissive, no backlight is required, allowing the Samsung OCTA display to deliver very high performance and exceptional display quality, with highly accurate and sensitivity-optimized touch input, in a module that is less than 2 mm thick and provides nearly 100-percent light transmission and exceptional outdoor visibility.

PenTile Display looks Pinkish?

Not really. When PenTile OLED is used in applications that run in 5-6-5 color modes, it’s possible for whites at low levels of luminance to have a quantization error that has slightly more red than green. As shown in the chromaticity chart below, such a minor shift away from white toward red or magenta is easily seen by the human vision system.  With displays of very high contrast any shift toward red will be perceived as pink. The very same displays where viewers saw such “pinkishness” showed no such artifact in other applications that were running in 24-bit color mode.

Image credit: http://lightemittingdiodes.org

 

 

Where Have I Seen PenTile Before?

PenTile technology has been incorporated into more than 70 high-resolution mobile products over the last three years, so you’ve seen it in a lot of places… though you may not have known it at the time.

There are two versions of this technology. One is called PenTile OLED, which has no white subpixel and uses an RGBG pattern of OLED subpixels. The other is PenTile RGBW technology.

PenTile OLED has been used most famously in phones like the Samsung Galaxy S and in digital cameras like the Samsung NX10.

PenTile RGBW LCDs have been used in phones like the Motorola Atrix.

It can just as easily be used in a GPS screen, portable video player, computer monitor, HDTV, electronic game or other high resolution phone or digital camera device.

The short answer to the question… you’ve seen PenTile displays all over the place.