All posts tagged RGBW

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.

Motorola Battery Indicator- Really a Color Error?

While I do not have the time to respond to everything that is written about PenTile technology, occasionally I will see something that is not quite right which is then picked up by other blogs and gets a life of its own. This can happen from a single photograph. Perhaps you have seen one or more recent blogs that claim that PenTile cannot render color correctly and then go on to illustrate this using the same badly focused photo.

Here is one that appeared today from androidphonetech.com.

As indicated by the logo, this photo seems to have originated with XDA.CN.

Several bloggers have shown this photo of a Motorola smartphone display stating that this proves that PenTile RGBW displays in Motorola’s phones exhibit this type of color error. I would be the first to agree that photographing high resolution displays is very challenging, especially at such high magnification. It is easy to overexpose the image, as was done here. Overexposure can cause color shifts, because the elements in the camera’s CCD of the proper color will become saturated and can no longer respond. Only at the right hand edge, where there is less light due to blur, did the camera capture the correct color.

Battery indicator on Motorola Atrix

With the proper exposure, from the equivalent display in a Motorola Atrix, you can see above that the highly magnified battery icon is rendered with the correct color over the entire area. You will see that there are more red subpixels on the top of this, since it was the intention to shade the green toward yellow at the top. And, here is the same photo, but zoomed in to show just the battery indicator:This photo matches exactly with what I see with my own eyes when looking through an eye loop.

Some of you may say it is different in a Droid X2 or another Motorola phone, but it is the same technology and the same PenTile firmware.

Of course, it was never intended that viewers examine these displays at this magnification, so you will see pattern visibility in these photos that is not apparent to people with normal vision for normal use. Fully saturated green on PenTile RGBW will have a bit of a checkerboard look that can be seen at this magnification. This does not occur with less saturated colors.

Finally, I tried to reproduce the color error by overexposing my photo of this same display and was able to reproduce the effect below. Of course, this will be slightly different for different cameras with different camera CCDs.

Battery Indicator Overexposed - note the yellow center with the green edge.

As you can see for yourself, PenTile RGBW is rendering the colors in this battery icon correctly in Motorola phone displays.

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.

 

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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.

OneIndia Video Post

There was some terrific video coverage of the new Samsung WQXGA, PenTile RGBW 300 dpi tablet panel that was shown at the recent SID DisplayWeek.

While this video mentions other high resolution tablets, no company, other than Samsung, has publicly demonstrated any 10.1-inch prototypes of more than 150 dpi to date.

This video raises lots of interesting questions about the application of this panel to products, but, as I have already said, Samsung is still in the prototype stage of product development  so you will not see any tablets with PenTile RGBW 300 dpi within this year.

Can PenTile RGBW be used for TV?

You bet!

Samsung SEC has built prototypes of a 32-inch FHD TV using PenTile RGBW with a white LED backlight.  This was demonstrated at the 2010 Flat Panel Display International (FPDI) conference in Makuhari, Japan.  This PenTile RGBW LCD  TV runs at about 55% the power of an equivalent brightness legacy RGB stripe panel showing the full range of multimedia applications.  The PenTile RGBW TV is capable of even higher savings for TV or video alone.

Due to the white subpixels, the white areas and reflections from things like the metal in a chrome bumper have a real zing that is not seen in conventional RGB stripe TVs.

Just like the mobile displays these are built with one-third fewer subpixels, but from only 2 meters away the pixels are seen as 48 cy/deg* of human vision where the pattern is not easily seen by the best of eyes.

* 48 cy/deg means that in one degree of human vision one can see 24 white lines and 24 black lines

Interface to a PenTile RGBW Display

We noticed some PenTile related comments in the Russian publication at HABRAHABR.RU.  Since so many readers of that site went to our blog, I thought it would be appropriate to answer a question raised there ( shown below for those who can read Russian).

Это понятно: попасть в устройство от Джобса лестно каждому. Но этому дисплею такая честь вряд ли светит: во-первых iPad использует другое соотношение сторон, во-вторых пикселы PenTile сильно отличаются от нормальных. Чтобы работать с таким дисплеем, программа должна понимать, что экран состоит не из пикселов, а из полупикселов двух разных типов. В основном это решается на уровне драйвера, но многие приложения придётся адаптировать. В-третьих такое разрешение даст слишком большую нагрузку для мобильных процессоров, что выльется в лаги и повышенное энергопотребление.
Но успехи в увеличении разрешения дисплеев радуют.

If we understand this correctly, there is some concern about connecting an existing system to a PenTile RGBW display panel.  It was correctly understood at this site that we have, to date, put the electronics for driving PenTile into the driver chip, but it was not clear how the signal had to be prepared to drive this display.

The answer is simple.  One feeds the display input a conventional RGB signal since the display module is plug and play.  Internally to the driver chip, we perform  a gamut mapping from RGB to RGBW.  The driver can handle 24-bit color, but if one puts in less bits of color the module will handle that as well.

Will RGBW help with a checkerboard pattern

The ability to observe pattern visibility is a function of visual acuity in cycles/degree of human vision and the size the pattern.  A person with the ability can see such a checkerboard pattern in a 4-inch WVGA pattern from normal viewing distance can also see stripe patterns on many popular RGB stripe panels being sold today.  For an RGBW panel the checkerboard pattern at the lower dpi range of PenTile OLED applications is only visible for fully saturated green or red on black. With an RGBW panel at any lesser color saturation the blacks in the checkerboard are filled in with the white subpixels to improve the brightness and to reduce this effect.

At 300 dpi on a tablet panel, which is typically viewed from 50% further away, about 18 inches, even the most saturated red and green on black as the worst case condition will not have any apparent checkerboard since the ability to resolve this will require vision of nearly 50 cycles/degree.  Few of us have vision which is that good.

So that brings me to the comment on zooming in to see text that is less clear.  First of all, your eyes do not have a zoom feature.  At least mine don’t.  These panels are designed to be viewed at a certain distance.  It is like saying that a tapestry when zoomed in shows the artifact of the stitches, or that a half tone print when zoomed in shows dots.  Of course they do, but that is not how they are used.  Secondly, if you do zoom in on black and white text, you will see the same detail in even single stroke fonts for PenTile as you do for RGB stripe.  Examples that have been shown in one recent blog say that it makes it look less sharp, but these images show otherwise.  Look at the black spot at the top of the “n”, where the curve meets the straight stem in the RGB stripe and compare that to PenTile. If it were less than sharp that single pixel black dot would not be there.

Single pixel dot at top of PenTile "n" is equal to RGB stripe

 

300 dpi is Fine but I Would Rather Have IPS

This is not an “either/ or” condition. This a case of having your cake and eating it too. PenTile RGBW technology is perfectly compatible with all types of wide viewing angle technology such as IPS, multidomain (PVA, MVA, etc). In fact, as a power saver it makes it a bit easier to use a wide viewing angle (WVA) technology with PenTile RGBW since many of these WVA techniques reduce light throughput.

IPS (in plane switching) was the name given to a type of WVA technology many years ago by Hitachi and was licensed to other display makers. Other variants of this methodology are in use by Samsung. Samsung uses a few different types of WVA technologies depending upon the application.

Perhaps there are some who are still asking, “Does a tablet PC that is being used by one person who is looking directly at the display really need WVA technology?”. The answer is a definite yes it does. Even a mobile display is used laying on the desk in front of you or held in your hands. Then consider viewing in both portrait or landscape modes and you realize that WVA capability is a generally a good idea.

So, here is the interesting thing about the new Samsung WQXGA PenTile RGBW prototype panel–it has a very wide viewing angle technology, not so different from IPS. Judge for yourself when you come see this at SID Display Week in LA this week.