do lcd displays update pixel by pixel quotation

Pixel pitch describes the density of the pixels (LED clusters) on an LED display and correlates with resolution. Sometimes referred to as pitch or dot pitch, the pixel pitch is the distance in millimeters from the center of a pixel to the center of the adjacent pixel. Since pixel pitch indicates the amount of space between two pixels, a smaller pixel pitch means there is less empty space between pixels. This equates to higher pixel density and improved screen resolution.

Pixel pitch is important because it influences the optimal viewing distance for your display. An image achieves smoother borders and finer detail with lower pixel pitch values. This allows the viewer to stand closer to the screen and enjoy a clear image without the distraction of discerning individual pixels. When determining viewing distance and pixel pitch, the rule of thumb is that a smaller pixel pitch allows for a closer viewing distance. Conversely, a higher pixel pitch elongates the minimum viewing distance. So, a 1.2mm screen will have significantly higher resolution and a closer optimal viewing distance than a 16mm .

While higher pixel density delivers improved visual quality, it is not the ideal option for every situation. Additional pixel density is intended for a closer viewing distance. At a greater viewing distance, higher pixel density loses its visual advantages and simply increases the cost of the display.

Consumers can get the best value for their LED screen by determining the optimal viewing distance of their screen. The optimal viewing distance is the point where image fidelity is retained, but if the observer moved much closer, the image quality would decrease or the screen would appear pixelated.

For example, a display with interactive touch solutions will need a low pixel pitch to produce crisp images for the nearby audience. On the other hand, an LED screen displayed above viewers, like one hung in an arena, could get away with a higher pixel pitch. The short answer is that a smaller pixel pitch will always give you better quality image, but the investment will not be fully appreciated if the screen is not seen from a sufficiently close enough distance.

Visual Acuity Distance – also known as retina distance, this is a formulated calculation of the distance a person with 20/20 vision must move away from an LED screen to see a coherent image that is not pixelated.

While these methodologies are useful guides, there is no correct answer in determining viewing distance. A screen’s viewing distance is ultimately whatever the owner of the screen finds comfortable.

In the past decade, LCD monitors have replaced CRT screens for all but the most specialist applications. Although liquid crystal displays boast perfect

You may experience a stuck pixel on a new or used LCD screen. If your monitor’s warranty has expired, or the manufacturer won’t replace the monitor because it considers one or two stuck pixels as acceptable, there are a few things that you can do.

This is obviously the safest method, but it’s not always effective. If you recently discovered a stuck pixel, you can try to turn off the monitor and unplug it for a day or two. When the damage is caused by overuse, this could help.

There are many websites that offer a stuck pixel fixing service. They work more or less in the same way, by flashing pixels and hopefully un-stick the ones that are defective.

You’ll find that many of them run with Flash, which is no longer available – fortunately, here’s one that you can still rely on – JScreenFix. JScreenFix is a free online service that can solve your problem of stuck pixels. You don’t have to download anything, so it’s not invasive nor harmful.

Visit the website jscreenfix.com and scroll down to find the Launch JScreenFix button – click on it. It will open a black screen with a square full of flickering pixels. The instructions pop up right there – however, what you’re meant to do is drag this square to the area where the stuck pixel is. Then, leave it for at least ten minutes.

If it doesn’t fix your stuck pixel on the first try, you can do a few attempts leaving it for a little longer. Usually, this method gets the job done, but it’s not a 100% guarantee.

*Safety note: If you have epilepsy, you should avoid using any of these stuck pixel fixer websites or software as they work with flashing erratic lights.

Any technique that implies applying pressure to fix a stuck pixel can potentially make more damage than good. Here you’ll find some precautions you should take to minimize these chances.

However, if you decide to do this, it’s at your own risk. Turn on your computer screen or monitor as the pixel needs to be working for the pressure methods to stand a chance.

Determine if you have hot, stuck or dead pixels – if you don’t know the difference among these, read the next section first. Only if the pixel is stuck, you’ll have a chance at fixing it with a pressure method.

Open a black image as background in full-screen mode or use a black browser window such as this. Either way, don’t just leave a blank signal. This again has to do with the fact that you need the pixel to have the backlight on. Make sure the screen is clean to avoid confusing dust with bad pixels.

Some people recommend a heat method where you use a hairdryer to warm the spot while you’re putting pressure on the monitor to fix a stuck pixel. Others suggest using a hot water damp cloth to apply the heat directly.

However, you could end up with something worse than a stuck pixel. The pressure method already represents a small risk of damaging your monitor – if you add heat, you’re increasing that risk.

To understand the possible pixel problems that you can face – and whether or not you can fix them – you need to know that an LCD screen is made by pixels. Three sub-pixels form each pixel – one is red, one is green, and one is blue (RGB).

When you have a pixel defect, it means that one or more of the subpixels aren’t working as they’re supposed to. Let’s see how these can present. Dead pixels

Dead pixels show no light, and what’s the absence of light? Dark. So, if you see a black pixel on your monitor, it’s a dead pixel. These are more noticeable when you’re working with a white background. Stuck pixels

The third option is that you see a white pixel – these are known as hot pixels. That means that all three colors (red, green and blue) are always on – this results in white light. These are more obvious on a dark background.

So, now you know what type of faulty pixels you can run into and how you can identify them. At this point, you might be wondering how do stuck pixels happen?

LCD stands for liquid crystal display. These monitors are made with multiple layers. In the far back, they have the light source that illuminates the screen with white even light.

The reason why we don’t see a fully white screen all the time is that there’s also a layer with color filters. This layer has a red, green and blue filter per pixel (RGB) – each of those would be a sub-pixel.

They can do this according to the amount of voltage. No voltage means that light can pass – full voltage blocks the light. Everything in between allows a different amount of light to pass through.

Anyway, all this explanation is to tell you that stuck or dead pixels often happen because there is a broken transistor that fails to supply voltage to a certain pixel or sub-pixel. Keep in mind that there are two types of LCD monitors: TN (Twisted Nematic) and IPS (In-Plane Switching). On TN monitors, the default without voltage is on. So, if the transistor is not supplying power, the pixel won’t be dead (black) but hot (white). On IPS monitors, it works the other way around.

So, you can use a dead pixel test. There are some free ones online such as the one from LCD Tech. You simply need to click on the Start Test button, and it will automatically enter full-screen mode in complete white.

Make sure your monitor is clean to identify dead pixels better. Because the screen will be completely white, you can also use this to find stuck pixels. On the other hand, a hot pixel won’t be visible – for these, you would need a dark screen.

Sometimes you can have bad luck and receive your new computer or monitor with an original pixel fault. In most cases, these are dead pixels, and therefore, there’s nothing you can do except try and exchange your monitor with the manufacturer.

Keep in mind that these are just good practices that can extend the life of your LCD screen. Unfortunately, there isn’t a full-proof method to avoid getting stuck pixels.

Stuck pixels are the most fixable problems you can have with your pixels. A stuck pixel can disappear on its own, or you can use other methods to try to fix it – in this article, you’ll find some of them.

It depends on the class of monitor that you have – only class I monitors shouldn’t have any dead pixels. For other classes, most manufacturers will consider one dead pixel as acceptable. This means that they probably won’t replace your new monitor because of it.

Of course, if this acceptable to you, it’s a different matter. It often depends on the location of the dead pixel and the size of the monitor. If you find it unacceptable, you should still give it a shot at the guarantee and see if you can have it exchanged. Check the ISO 13406-2 to see the ‘acceptable’ standards according to the type of monitor.

No, dead pixels won’t go away on their own – most of the times, they’re not even fixable. Before you give up, though, make sure the pixel is really dead and not stuck – because stuck pixels can go away.

Dead pixels are more noticeable in light areas because they are black. Also, it depends on the size of the pixel, the size of the display and the resolution. Keep in mind that once you know it’s there, you’ll keep noticing it.

If your warranty is valid and you can get your device exchanged, that’s the best way to do it. Otherwise, determine what type of pixel problem you have.

There are a few different methods to try to fix stuck pixels – although none of them is certain. On the other hand, hot and dead pixels can’t be fixed.

I hope you found this guide helpful. If you have any questions or want to share some tips on preventing, detecting, and fixing faulty pixels, please leave a comment.

Subpixel rendering technology. From left to right: no anti-aliasing, subpixel rendering, anti-aliasing, subpixel rendering with anti-aliasing. Click to see the full-size image.

Subpixel rendering works by increasing the luminance reconstruction points of a color subpixelated screen, such as a liquid crystal display (LCD) or organic light-emitting diode (OLED) display. This thumbnail image is downsized and does not show the technique. Click to see the full-size image.

Subpixel rendering is a way to increase the apparent resolution of a computer"s liquid crystal display (LCD) or organic light-emitting diode (OLED) display by rendering pixels to take into account the screen type"s physical properties. It takes advantage of the fact that each pixel on a color LCD is actually composed of individual red, green, and blue or other color subpixels to anti-alias text with greater detail or to increase the resolution of all image types on layouts which are specifically designed to be compatible with subpixel rendering.

Examples of pixel geometry, showing various arrangements of pixels and subpixels, which must be considered for subpixel rendering. LCD displays (bottom right is the most typical example) are best suited to subpixel rendering.

A single pixel on a color subpixelated display is made of several color primaries, typically three colored elements—ordered (on various displays) either as blue, green, and red (BGR), or as red, green, and blue (RGB). Some displays have more than three primaries, often called MultiPrimary, such as the combination of red, green, blue, and yellow (RGBY), or red, green, blue and white (RGBW), or even red, green, blue, yellow, and cyan (RGBYC).

These pixel components, sometimes called subpixels, appear as a single color to the human eye because of blurring by the optics and spatial integration by nerve cells in the eye. The components are easily visible, however, when viewed with a small magnifying glass, such as a loupe. Over a certain resolution threshold the colors in the subpixels are not visible, but the relative intensity of the components shifts the apparent position or orientation of a line.

Subpixel rendering is better suited to some display technologies than others. The technology is well-suited to LCDs and other technologies where each logical pixel corresponds directly to three or more independent colored subpixels, but less so for CRTs.

In a CRT the light from the pixel components often spreads across pixels, and the outputs of adjacent pixels are not perfectly independent. If a designer knew precisely about the display"s electron beams and aperture grille, subpixel rendering might have some advantage but the properties of the CRT components, coupled with the alignment variations that are part of the production process, make subpixel rendering less effective for these displays.

The technique should have good application to organic light emitting diodes (OLED) and other display technologies that organize pixels the same way as LCDs.

Pixels on an LCD are made up of separate red, green, and blue elements, which can be used to give finer control over rendering the curvature of text. The word would appear white on the screen because red, green, and blue light combined are indistinguishable from white light to the human visual system.

The origin of subpixel rendering as used today remains controversial. Apple, then IBM, and finally Microsoft patented various implementations with certain technical differences owing to the different purposes their technologies were intended for.

Microsoft has several patents in the United States on subpixel rendering technology for text rendering on RGB Stripe layouts. The patents 6,219,025, 6,239,783, 6,307,566, 6,225,973, 6,243,070, 6,393,145, 6,421,054, 6,282,327, 6,624,828 were filed between October 7, 1998, and October 7, 1999, thus should expire on October 7, 2019.

It is sometimes claimed (such as by Steve GibsonApple II, introduced in 1977, supports an early form of subpixel rendering in its high-resolution (280×192) graphics mode. However, the method Gibson describes can also be viewed as a limitation of the way the machine generates color, rather than as a technique intentionally exploited by programmers to increase resolution.

Under the current US regime, any minor improvement to a previous technique can be considered an "invention" and "protected" by a patent under the right circumstances (e.g. if it"s not totally trivial), If [

The bytes that comprise the Apple II high-resolution screen buffer contain seven visible bits (each corresponding directly to a pixel) and a flag bit used to select between purple/green or blue/orange color sets. Each pixel, since it is represented by a single bit, is either on or off; there are no bits within the pixel itself for specifying color or brightness. Color is instead created as an artifact of the NTSC color encoding scheme, determined by horizontal position: pixels with even horizontal coordinates are always purple (or blue, if the flag bit is set), and odd pixels are always green (or orange). Two lit pixels next to each other are always white, regardless of whether the pair is even/odd or odd/even, and irrespective of the value of the flag bit. The foregoing is only an approximation of the true interplay of the digital and analog behavior of the Apple"s video output circuits on one hand, and the properties of real NTSC monitors on the other hand. However, this approximation is what most programmers of the time would have in mind while working with the Apple"s high-resolution mode.

Gibson"s example claims that because two adjacent bits make a white block, there are in fact two bits per pixel: one which activates the purple left half of the pixel, and the other which activates the green right half of the pixel. If the programmer instead activates the green right half of a pixel and the purple left half of the next pixel, then the result is a white block that is 1/2 pixel to the right, which is indeed an instance of subpixel rendering. However, it is not clear whether any programmers of the Apple II have considered the pairs of bits as pixels—instead calling each bit a pixel. While the quote from Apple II inventor Steve Wozniak on Gibson"s page seems to imply that vintage Apple II graphics programmers routinely used subpixel rendering, it is difficult to make a case that many of them thought of what they were doing in such terms.

The flag bit in each byte affects color by shifting pixels half a pixel-width to the right. This half-pixel shift was exploited by some graphics software, such as HRCG (High-Resolution Character Generator), an Apple utility that displayed text using the high-resolution graphics mode, to smooth diagonals. (Many Apple II users had monochrome displays, or turned down the saturation on their color displays when running software that expected a monochrome display, so this technique was useful.) Although it did not provide a way to address subpixels individually, it did allow positioning of pixels at fractional pixel locations and can thus be considered a form of subpixel rendering. However, this technique is not related to LCD subpixel rendering as described in this article.

Microsoft announced its subpixel rendering technology, called ClearType, at COMDEX in 1998.Displaced Filtering for Patterned Displays describing the filtering behind ClearType.Windows XP, but it was not activated by default until Windows Vista. (Windows XP OEMs however could and did change the default setting.)

FreeType, the library used by most current software on the X Window System, contains two open source implementations. The original implementation uses the ClearType antialiasing filters and it carries the following notice: "The colour filtering algorithm of Microsoft"s ClearType technology for subpixel rendering is covered by patents; for this reason the corresponding code in FreeType is disabled by default. Note that subpixel rendering per se is prior art; using a different colour filter thus easily circumvents Microsoft"s patent claims."

Since version 2.8.1, a second implementation exists, called Harmony, that "offers high quality LCD-optimized output without resorting to ClearType techniques of resolution tripling and filtering". This is the method enabled by default. When using this method, "each color channel is generated separately after shifting the glyph outline, capitalizing on the fact that the color grids on LCD panels are shifted by a third of a pixel. This output is indistinguishable from ClearType with a light 3-tap filter."

David Turner was however skeptical of SubLCD"s author"s claims: "Unfortunately, I, as the FreeType author, do not share his enthusiasm. The reason is precisely the very vague patent claims [by Microsoft] described previously. To me, there is a non-negligible (even if small) chance, that these claims also cover the SubLCD technique. The situation would probably be different if we could invalidate the broader patent claims, but this is not the case currently."

Adobe built their own subpixel renderer called CoolType, so they could display documents the same way across various operating systems: Windows, MacOS, Linux etc. When it was launched around the year 2001, CoolType supported a wider range of fonts than Microsoft"s ClearType, which was then limited to TrueType fonts, whereas Adobe"s CoolType also supported PostScript fonts (and their OpenType equivalent as well).

Mac OS X used to use subpixel rendering as well, as part of Quartz 2D, however it was removed after the introduction of Retina displays. Unlike Microsoft"s implementation, which favors a tight fit to the grid (font hinting) to maximize legibility, Apple"s implementation prioritizes the shape of the glyphs as set out by their designer.

Starting in 1992, Candice H. Brown Elliott researched subpixel rendering and novel layouts, the PenTile matrix family pixel layout, which worked together with sub pixel rendering algorithms to raise the resolution of color flat-panel displays.Samsung purchased Clairvoyante and simultaneously funded a new company, Nouvoyance, Inc., retaining much of the technical staff, with Ms. Brown Elliott as CEO.

With subpixel rendering technology, the number of points that may be independently addressed to reconstruct the image is increased. When the green subpixels are reconstructing the shoulders, the red subpixels are reconstructing near the peaks and vice versa. For text fonts, increasing the addressability allows the font designer to use spatial frequencies and phases that would have created noticeable distortions had it been whole pixel rendered. The improvement is most noted on italic fonts which exhibit different phases on each row. This reduction in moiré distortion is the primary benefit of subpixel rendered fonts on the conventional RGB Stripe panel.

Although subpixel rendering increases the number of reconstruction points on the display this does not always mean that higher resolution, higher spatial frequencies, more lines and spaces, may be displayed on a given arrangement of color subpixels. A phenomenon occurs as the spatial frequency is increased past the whole pixel Nyquist limit from the Nyquist–Shannon sampling theorem; Chromatic aliasing (color fringes) may appear with higher spatial frequencies in a given orientation on the color subpixel arrangement.

Shown below is an example of black and white lines at the Nyquist limit, but at a slanting angle, taking advantage of subpixel rendering to use a different phase each row:

This case shows the result of attempting to place vertical black and white lines at four subpixels per cycle on the RGB Stripe architecture. One can visually see that the lines, instead of being white, are colored. Starting from the left, the first line is red combined with green to produce a yellow-colored line. The second line is green combined with blue to produce a pastel cyan-colored line. The third line is blue combined with red to produce a magenta-colored line. The colors then repeat: yellow, cyan, and magenta. This demonstrates that a spatial frequency of one cycle per four subpixels is too high. Attempts to go to a yet higher spatial frequency, such as one cycle per three subpixels, would result in a single solid color.

Some LCDs compensate the inter-pixel color mix effect by having borders between pixels slightly larger than borders between subpixels. Then, in the example above, a viewer of such an LCD would see a blue line appearing adjacent to a red line instead of a single magenta line.

Novel subpixel layouts have been developed to allow higher real resolution without chromatic aliasing. Shown here is one of the member of the PenTile matrix family of layouts. Shown below is an example of how a simple change to the arrangement of color subpixels may allow a higher limit in the horizontal direction:

In this case, the red and green order are interchanged every row to create a red & green checkerboard pattern with blue stripes. Note that the vertical subpixels could be split in half vertically to double the vertical resolution as well : the current LCD panels already typically use two color LEDs (aligned vertically and displaying the same lightness, see the zoomed images below) to illuminate each vertical subpixel. This layout is one of the PenTile matrix family of layouts. When displaying the same number of black-white lines, the blue subpixels are set at half brightness "b":

Notice that every column that turns on comprises red and green subpixels at full brightness and blue subpixels at half value to balance it to white. Now, one may display black and white lines at up to one cycle per three subpixels without chromatic aliasing, twice that of the RGB Stripe architecture.

Variants of the previous layout have been proposed by Clairvoyante/Nouvoyance (and demonstrated by Samsung) as members of the PenTile matrix family of layouts specifically designed for subpixel rendering efficiency.

For example, taking advantage of the doubled visible horizontal resolution, one could double the vertical resolution to make the definition more isotropic. However this would reduce the aperture of pixels, producing lower contrasts. A better alternative uses the fact that the blue subpixels are those that contribute the least to the visible intensity, so that they are less precisely located by the eye. Blue subpixels are then rendered just as a diamond in the center of a pixel square, and the rest of the pixel surface is split in four parts as a checker board of red and green subpixels with smaller sizes. Rendering images with this variant can use the same technique as before, except that now there"s a near-isotropic geometry that supports both the horizontal and the vertical with the same geometric properties, making the layout ideal for displaying the same image details when the LCD panel can be rotated.

The doubled vertical and horizontal visual resolution allows to reduce the subpixel density of about 33%, in order to increase their aperture also of about 33%, with the same separation distance between subpixels (for their electronic interconnection), and also to reduce the power dissipation of about 50% with a white/black contrast increased of about 50% and still a visual-pixel resolution enhanced by about 33% (i.e. about 125 dpi instead of 96 dpi), but with only half the total number of subpixels for the same displayed surface.

Another variant, called the RGBW Quad, uses a checkerboard with 4 subpixels per pixel, adding a white subpixel, or more specifically, replacing one of the green subpixels of Bayer filter Pattern with a white subpixel, to increase the contrast and reduce the energy needed to illuminate white pixels (because color filters in classic RGB striped panels absorb more than 65% of the total white light used to illuminate the panel). As each subpixel is a square instead of a thin rectangle, this also increases the aperture with the same average subpixel density, and same pixel density along both axis. As the horizontal density is reduced and the vertical density remains identical (for the same square pixel density), it becomes possible to increase the pixel density of about 33%, while maintaining the contrast comparable to classic RGB or BGR panels, taking profit of the more efficient use of light and lowered absorption levels by the color filters.

It is not possible to use subpixel rendering to increase the resolution without creating color fringes similar to those seen in classic RGB or BGR striped panels, but the increased resolution compensates it, in addition, their effective visible color is reduced by the presence of "color-neutral" white subpixels.

Yet another variant, a member for the PenTile matrix family of subpixel layouts, alternates between subpixel order RGBW / BWRG every other row, to allow subpixel rendering to increase the resolution, without chromatic aliasing. As before, the increased transmittance using the white subpixel allows higher subpixel density, but in this case, the displayed resolution is even higher due to the benefits of subpixel rendering:

However, such alternate layouts are still not compatible with subpixel rendering font algorithms used in Windows, Mac OS X and Linux, which currently support only the RGB or BGR horizontal striped subpixel layouts (rotated monitor subpixel rendering is not supported on Windows or Mac OS X, but Linux does for most desktop environments). However, the PenTile matrix displays have a built-in subpixel rendering engine that allows conventional RGB data sets to be converted to the layouts, providing plug"n"play compatibility with conventional layout displays. New display models should be proposed in the future that will allow monitor drivers to specify their visual resolution separately from the full pixel resolution and the relative position offsets of visible subpixels for each color plane, as well as their respective contribution to white intensity. Such monitor drivers would allow renderers to correctly adjust their geometry transform matrices in order to correctly compute the values of each color plane, and take the best profit of subpixel rendering with the lowest chromatic aliasing.

Photos were taken with a Canon PowerShot A470 digital camera using "Super Macro" mode and 4.0× digital zoom. The screen used was that integrated into a Lenovo G550 laptop. Note that the display has RGB pixels. Displays exist in all four patterns horizontal RGB/BGR and vertical RGB/BGR but horizontal RGB is the most common. In addition, several color subpixel patterns have been developed specifically to take advantage of subpixel rendering. The best known of these is the PenTile matrix family of patterns.

The composite photographs below show three methods of fonts rendering for comparison. From top: Monochrome; Traditional (whole pixel) spatial anti-aliasing; Subpixel rendering.

David Turner (24 Sep 20:00 2006) LCD Rendering Patches Archived 2007-02-08 at the Wayback Machine (was Re: [ft] Regression in rendering quality with subpixel antialiasing)

Platt, John; Keely, Bert; Hill, Bill; Dresevic, Bodin; Betrisey, Claude; Mitchell, Don P.; Hitchcock, Greg; Blinn, Jim; Whitted, Turner (2000-05-01). "Displaced Filtering for Patterned Displays": 296–299. Cite journal requires |journal= (help)

Brown Elliott, C.H., "Reducing Pixel Count without Reducing Image Quality" Archived 2012-03-02 at the Wayback Machine, Information Display Magazine, December 1999, ISSN 0362-0972

Many Apple products use liquid crystal displays (LCD). LCD technology uses rows and columns of addressable points (pixels) that render text and images on the screen. Each pixel has three separate subpixels—red, green and blue—that allow an image to render in full color. Each subpixel has a corresponding transistor responsible for turning that subpixel on and off.

Depending on the display size, there can be thousands or millions of subpixels on the LCD panel. For example, the LCD panel used in the iMac (Retina 5K, 27-inch, 2019) has a display resolution of 5120 x 2880, which means there are over 14.7 million pixels. Each pixel is made up of a red, a green, and a blue subpixel, resulting in over 44 million individual picture elements on the 27-inch display. Occasionally, a transistor may not work perfectly, which results in the affected subpixel remaining off (dark) or on (bright). With the millions of subpixels on a display, it is possible to have a low number of such transistors on an LCD. In some cases a small piece of dust or other foreign material may appear to be a pixel anomaly. Apple strives to use the highest quality LCD panels in its products, however pixel anomalies can occur in a small percentage of panels.

In many cases pixel anomalies are caused by a piece of foreign material that is trapped somewhere in the display or on the front surface of the glass panel. Foreign material is typically irregular in shape and is usually most noticeable when viewed against a white background. Foreign material that is on the front surface of the glass panel can be easily removed using a lint free cloth. Foreign material that is trapped within the screen must be removed by an Apple Authorized Service Provider or Apple Retail Store.

If you are concerned about pixel anomalies on your display, take your Apple product in for closer examination at an Apple Store, Apple Authorized Service Provider, or an Independent Repair Provider. There may be a charge for the evaluation. Genuine Apple parts are also available for out-of-warranty repairs through Self Service Repair.*

Update: This post was originally written several years ago, as a discussion of the iPhone 4 and the “Retina Display” marketing term. The original post was quite outdated but the discussion of LCDs versus physical printing is still relevant.

Back when I wrote the original article, I had several private conversations with experts in realtime graphics. They were seriously talking about maybe we don’t need AA any more because the resolution of displays is so high that AA becomes unneccessary. That was scary to me, because if the experts who are giving presentations a Siggraph don’t understand this, then what hope does everyone else have?

Over the last 5 years, it seems like truth has triumphed over lies. Everyone I talk to in computer graphics has a good grasp of aliasing. So this post has been updated and targeted to newcomers who have questions.

As you may have heard, the term “Retina Display” started with the iPhone 4, which has 326 DPI (dots per inch). Since the resolution of the display is higher than the human retina at typical viewing distances, the marketing message is that it is the best display possible. The display is so good that if you had a better display then you wouldn’t be able to tell the difference. Technically “Retina Display” is just an Apple marketing term, but the marketing narrative was pretty clear. Here is the exact quote from Steve Jobs:

“It turns out there’s a magic number right around 300 pixels per inch, that when you hold something around to 10 to 12 inches away from your eyes, is the limit of the human retina to differentiate the pixels.”

Thanks to the Retina display, everything you see and do on iPhone 4 looks amazing. That’s because the Retina display’s pixel density is so high, your eye is unable to distinguish individual pixels. Which means Text in books, web pages, and email is crisp at any size. Images in games, movies, and photos pop off the screen. And everything is sharper.

Instead of talking about the theory of human vision, let’s just test this on your screen with your eyes right now. Then we’ll talk about theory. If you look at this on your phone, you have to make sure that your phone is displaying these images with a 1:1 pixel ratio.

There are two kinds of crosses here. One set of crosses is made by solid lines, and the other one from stippled dots. As you get farther from the screen, both crosses will start to look the same, although one set of crosses might be brighter or darker than the other depending on gamma. Anyways, take a note of how far away you have to be for the dots to blur together.

For most of you, you are viewing this page on a desktop. You can do the math and figure out the DPI of your monitor, but it’s probably about 100. For me, that distance is about 5 feet. At 3 feet I can clearly see the dots, and at 5 feet I can tell the intensity difference between the crosses, but I can’t discern the dots. So a “Retina Display” would hit the resolvable resolution limit for me eyes with a DPI of 500. But is that the real test of the limits of my visual system?

What you might like to know is that 1 dot is not 1 dot. Here is another image. This image contains both jagged lines and anti-aliased lines. Now do the same thing and keep going back until you can’t see the jaggies in the lines.

For me, that distance is somewhere around 10 feet. At 6 feet, the anti-aliased lines are really obvious. At 8, I have to focus, but I can clearly see some kind of waviness in the nearly horizontal and nearly vertical lines. Btw, I have decent vision, but not great. I wear contacts with a prescription of -2.25. With correction, I might be slightly better than 20/20, but I’m definitely not a sharp-sighted freak of nature. Yet by my calculations, in the second image, I’m able to see artifacts even at a size equivalent to 1000 DPI, slightly higher than the “Retina Display” with 326. Also, the lines example is not actually the worst-case for aliasing. If the image were rotating slowly, you would be able to see “crawling jaggies”, which are even more noticeable.

Then again, what are you doing right now? Well, you’re reading black text on a white background! These sharpness tests aren’t ridiculous scenarios, they are in fact the most common use case!

Essentially, it’s not possible to make a “Vernier Caliper” app on your iPhone 4. With a vernier caliper, you have to determine which sets of lines are aligned or not aligned to figure out the last decimal place of your measurement. You can’t simulate this on your iPhone 4 because it doesn’t have enough resolution to create those sharp, misaligned lines at a typical viewing distance.

Most people think about the human eye as if it is like an LCD display. We have rods and cones which sense brightness and color. And most people think that that signal is fed directly into our brain. In reality, that’s not what we see at all. We see a highly processed version. If you want to learn more about this, I highly recommend that you get a copy of “The Biology of Seeing” by Margaret Livingstone. Also, thanks go to David Luebke of NVIDIA (one of our best champions in the gamma war) for sending me some info on this.

Vernier acuity measures the ability to align two line segments. Humans can do this with remarkable accuracy. Under optimal conditions of good illumination, high contrast, and long line segments, the limit to vernier acuity is about 8 arc seconds or 0.13 arc minutes, compared to about 0.6 arc minutes (20/12) for normal visual acuity or the 0.4 arc minute diameter of a foveal cone. Because the limit of vernier acuity is well below that imposed on regular visual acuity by the “retinal grain” or size of the foveal cones, it is thought to be a process of the visual cortex rather than the retina. Supporting this idea, vernier acuity seems to correspond very closely (and may have the same underlying mechanism) enabling one to discern very slight differences in the orientations of two lines, where orientation is known to be processed in the visual cortex.

Another important consideration is the surface tension of ink. When you have two water droplets next to each other, and they barely touch, you don’t see a hard edge between them. Instead, they combine into one smooth drop because of surface tension. You can look it up, but the basic idea is that water droplets want to have as little surface area as possible for their given volume. So when two water drops barely touch, they combine into one larger drop to minimize the surface area.

The same thing happens with ink. If you print an aliased edge of dotted ink droplets, the drops merge together and smooth out the lines. That does not happen on a computer screen. With ink, even at 150 dpi, you wouldn’t see any aliasing problems. And with water droplets, at 5 dpi you probably won’t see any aliasing as long as they touch.

Also, in Steve Jobs’s quote, he says that 300 DPI is commonly accepted as good enough. Is this true? Not really. For images, yes, 300 DPI is the common standard (such as for stock photos). For text, not at all. For example, my printer does not have a 300 DPI setting. I can choose either 600 or 1200. No one prints the text for magazines at 300 DPI.

Here are some screenshots comparing the Kindle to the iPad to Magazines/Books/Newspaper. Of course those tests are looking at an iPad, not an iPhone 4. So for the iPad images, imagine the same thing but smaller. With the ink examples notices how you don’t have any harsh aliased edges anywhere. That’s because ink naturally smooths itself out, whereas the iPad has harsh aliasing problems, and so does the Kindle to a lesser degree.

Wow. Even if we were to triple the iPad’s resolution to get it up to the iPhone 4, it would still get destroyed by the magazine print. Also, look at the “y”. Notice how even though it’s slanted, you get a perfectly crisp line. For any lines that are angled (as opposed to vertical or horizontal) on the iPad, you have to make the pixels on the edge half-bright or so. Yeah, those printing guys know what they’re doing.

And yes, this level of quality does make a difference. As a test compare a typical printed novel to a high-quality magazine. If you are like me, the magazine text feels crisper and cleaner than the novel. The difference is not life-changing, but still noticeable.

It will be a long long time before we have screens that display text as well as a magazine does. They are printed with several times more resolution than an 300 DPI, and getter better quality from the ink. By my estimate, you would need at least 10x more pixels per square inch to match the quality of print.

Minute dots( bright dots and/or dark dots as seen above) may occur on a LCD. These dots are called Defective pixels (quoted from Wikipedia)". These dots may or may not stand out according to the colors displayed. It is a characteristic of LCDs and are not a defect and cannot be completely avoided with todays manufacturing technology.

A dot that is always off unlit even after the display is turned on (all dots are turned on). It shows as either a black dot or dot of other colors other than white on a white display.

The backlight emits white light, through the polarizer for the initial handsome selection of light, through the glass plate to reach the liquid crystal control circuit, light through the liquid crystal gap, the external voltage applied to the liquid crystal, will change the angle of light deflection, light in the glass plate, through the polarizer, and finally projected on the red, green and blue polarizer, showing different colors, and finally formed a display unit, called pixel points

LCD itself does not emit light, the backlight is required to provide a light source, light through a series of processing to the output, the output light intensity is much lower than the intensity of the light source, the energy utilization rate is lower, (energy-saving than CRT displays), LCD processing, will lead to a narrower display direction, corresponding to its perspective is smaller, from the side of the screen will not be able to see his display content, color conversion, liquid crystal molecules also need to consume a certain amount of time to rotate, resulting in a low response speed of the screen

Larger screen for outdoor use, using LED dot matrix color display, each pixel, containing red, green and blue LED lights, display principle similar to the LED color lights on the experimental board

OLED display and LED dot true color display principle is similar, because it uses the pixel unit is “Organic Light Emitting Diode (Organic Light EmitTIng Diode)” pixel density is much higher than the ordinary LED dot matrix display

OLED displays do not need backlight, high contrast ratio, thin and light, wide viewing angle, fast response time and other advantages, the price is higher

Pixel: The most basic display unit element of the image, the display pixel refers to the smallest point of his imaging Embedded devices, the display is described as “row pixel value * column pixel value” The color reference color on the display, red, green and blue RGB888 indicates that the color is expressed using 8bit RGB565, corresponding to red 5bit, green 6bit, blue 5bit Color depth indicates the number of bits corresponding to each pixel 16bit or 24bit, 24bit is sufficient for regular use

Each pixel in the LCD screen is data, in practice, it is necessary to cache the data of each pixel and then transfer it to the LCD screen, this way of storing display data is called memory.

The answer is yes. You should change the screen completely. Your screen has part of the LCD broken, so it is not possible to repair. You can change the glass, but the spot on the LCD has no repair.

If you’re designing a display application or deciding what type of TV to get, you’ll probably have to choose between an OLED or LCD as your display type.

Not sure which one will be best for you? Don’t worry! We’re here to help you figure out the right display for your project or application. In this post we’ll break down the pros and cons of these display types so you can decide which one is right for you.

LCDs utilize liquid crystals that produce an image when light is passed through the display. OLED displays generate images by applying electricity to organic materials inside the display.OLED and LCD Main Difference:

graphics and images visible. This is the reason you’re still able to see light coming through on images that are meant to be dark on an LCD monitor, display, or television.

OLEDs by comparison, deliver a drastically higher contrast by dynamically managing their individual pixels. When an image on an OLED display uses the color black, the pixel shuts off completely and renders a much higher contrast than that of LCDs.OLED vs LCD - Who is better at contrast?

Having a high brightness level is important if your display is going to be used in direct sunlight or somewhere with high ambient brightness. The display"s brightness level isn"t as important if it’s going to be used indoors or in a low light setting.OLED vs LCD - Who is better at Brightness?

Have you ever looked at a screen from an angle and noticed that the images became washed out or shadowy? The further away you get from the “front and center” view, the worse the image appears to be. This is an example of viewing angles in action – the wider the viewing angle, the better the images on screen will appear as you view them from different vantage points.

This means the display is much thinner than LCD displays and their pixels are much closer to the surface of the display, giving them an inherently wider viewing angle.

You’ll often notice images becoming distorted or losing their colors when tilting an LCD or when you view it from different angles. However, many LCDs now include technology to compensate for this – specifically In-Plane Switching (IPS).

LCDs with IPS are significantly brighter than standard LCDs and offer viewing angles that are on-par with OLEDs.OLED vs LCD - Who is better at Viewing Angles?

LCDs have been on the market much longer than OLEDs, so there is more data to support their longevity. On average LCDs have proven to perform for around 60,000 hours (2,500) days of operation.

With most LCDs you can expect about 7 years of consistent performance. Some dimming of the backlight has been observed but it is not significant to the quality of the display.

OLEDs are a newer technology in the display market, which makes them harder to fully review. Not only does OLED technology continue to improve at a rapid pace, but there also hasn’t been enough time to thoroughly observe their performance.

You must also consider OLED’s vulnerability to image burn-in. The organic material in these displays can leave a permanent afterimage on the display if a static image is displayed for too long.

So depending on how your OLED is used, this can greatly affect its lifespan. An OLED being used to show static images for long periods of time will not have the same longevity as one displaying dynamic, constantly moving images.OLED vs LCD - Which one last longer?

There is not yet a clear winner when it comes to lifespans between LCD and OLED displays. Each have their advantages depending on their use-cases. It’s a tie!

SEOUL (Reuters) - Liquid-crystal display (LCD) screens were expected to slowly fade and die, giving way to lighter, thinner and tougher organic light-emitting diode (OLED) panels in everything from smartphones to televisions.A man watches Sharp"s television sets at an electronic shop in Tokyo in this March 19, 2012 file photo. REUTERS/Kim Kyung-Hoon/Files

But LCD is refusing to go quietly as its picture quality keeps getting better. At the same time, the major backers of credit card-thin OLED panels - led by Samsung Electronics Coand LG Electronics Inc- are struggling to make the technology cheap enough to mass produce. The two South Korean firms this year showcased 55-inch (140 cm) OLED TVs, but priced at around $10,000 (6,220 pounds) - 10 times that of an LCD equivalent - they have yet to reach store shelves.

OLED displays, used on Samsung’s Galaxy S and Note smartphones, have been touted as the future display model to replace LCDs across the consumer electronics spectrum - from TVs to computers, laptops, tablets and smartphones. OLED is more energy efficient and offers higher contrast images than LCD, and is so thin that future mobile devices will be unbreakable, and will be able to be folded or rolled up like a newspaper.

But OLED panel makers such as Samsung Display and LG Displayhave yet to address major manufacturing challenges to lower costs to compete against LCD panels.

At the same time, LCD panels, which are used on 9 of every 10 television sets, are still evolving and show no sign of giving way in this latest battle to set the global standard - less than a decade since LCD effectively killed off plasma screens.

“OLED still has a long way to go to become a mainstream display, as it has to become bigger and improve picture quality,” said Chung Won-seok, an analyst at HI Investment & Securities. “The use of OLEDs will continue to be confined to small displays at least for the next 2-3 years. Its usage as a mainstream TV panel is only likely in 2014, but even then there’s a possibility of intense competition with LCD TVs as that technology keeps improving.”

Far from fading, LCD panels now offer better picture quality - up to four times better than OLED - and use less power, creating robust demand from smartphone and tablet makers.

As has often been the case, Apple Incmoved the goalposts by upgrading the display resolution for its iPhone and iPad, still the high-end LCD market"s gold standard, prompting rivals to upgrade their display panel qualifications. Analysts at Macquarie predict Apple will adopt high-resolution screens for the MacBook Air and iMac monitor next year, accelerating the industry"s shift to high-resolution displays.

Taiwan"s HTC Corphas introduced the Droid DNA smartphone with a 440 pixel per inch (ppi) density - the sharpest smartphone screen yet, with far higher resolution than the iPad"s 330 ppi and the iPhone 5"s 326 ppi. Samsung"s Galaxy S III, which uses an OLED screen, has 306 ppi density.

"The pixel war is an absolute bonanza for LCD makers," said Kim Byung-ki, analyst at Kiwoom Securities. "Manufacturers from LG Display to Samsung, Sharp Corp, AU Optronics Corpand Chimei (Innolux)all will gradually convert their traditional lines into more high-end product fabs, and that will curtail supply and boost profitability."

These higher-resolution panels cost more than double the commodity-type LCD screens, boosting panel producers’ profits. Even Samsung, the standard bearer for OLED panels and also a major LCD manufacturer, is actively promoting LCD screens for tablets and laptops over OLED, said a person familiar with the matter, who was not authorised to talk to the media so didn’t want to be named.

Both Sony and LG Electronics now sell ultra HD (high definition) LCD sets that boast four times the picture quality of HD TVs. The two firms, which are selling 84-inch TVs, aim to reduce that size to cater for more popular smaller sets.

To squeeze more pixels per inch, panel makers are upgrading their thin-film transistor (TFT) panel production facilities to new IGZO or LTPS processing technologies that require almost twice as many processing steps and which suffer higher faulty product rates and lost output.

Japan’s Sharp is the frontrunner in IGZO technology, which uses indium gallium zinc oxide instead of amorphous silicon, in panel manufacturing. LG Display, a major supplier to Apple, is investing 1.2 trillion won ($1.1 billion) by end-2013 in its production of low-temperature poly silicon (LTPS) panels - a technology used to make screens for the iPhone and iPad.

While new technologies can be game-changers, these panels are not simple to produce, limiting availability and driving up manufacturing costs. Some warn of an LCD supply shortage.

“The LCD industry is improving more strongly than expected and panels are likely to be in short supply from 2013, as manufacturers upgrade their lines to increase high-end products. This requires more processing time and steps, reducing total output,” said Kim Dong-won, an analyst at Hyundai Securities.

As LCD prospects improve, LG Display, the world’s top LCD maker, swung to a quarterly profit in July-September, ending a run of seven straight quarterly losses.

LG Display is expected to continue its solid performance, as Apple buys fewer parts from rival Samsung and moves more to high-end displays on a wider range of its products. LG Display shares have risen by around a third in 3 months, double Samsung"s gains. In Taiwan, AU Optronics shares are up 41 percent over that same period and Chimei is up 45 percent. Shares in cash-strapped Sharp hit a 2-month high on Wednesday after the company secured an up to $120 million cash injection from Qualcomm Inc, which will help it fund development of its IZGO technology.

“LG Display and its peers are actually sowing the seeds of the next cycle downturn by doing what they always do - wherever they see a profit opportunity, they focus on it, adding capacity and dissipating the excess returns,” said Stanford Bernstein analyst Alberto Moel.

Deciding when it’s time to replace your digital display can be tough. After all, you want to get as much use as possible out of your investment. But even the best displays don’t last forever. It’s important to consider upgrading your LED display to not only remain competitive and compliant, but also to avoid having to use more power to keep it running. With a newer setup, you can ensure lower energy costs and worry less about downtime.

Even with the best maintenance, displays are subject to mechanical issues and failure. Older displays, especially those outdoors, receive a lot of environmental wear and tear over the years. Sunlight fades and degrades individual diodes, decreasing display brightness and picture consistency. With an inconsistent picture, your display is less valuable to both you and your advertisers. And as with any aging product, parts can fail. It happens, and without a warranty to replace or repair, those parts can be a big hit to your budget — if you can find obsolete parts at all.

With rapid advancements in display technology, an upgrade may be necessary to stay competitive or compliant. Samsung’s MagicINFO, an all-in-one digital signage platform, is also an option that can help you manage the software and the hardware of your LED displays and optimize their performance, all from one place.

Pixel pitch has continued to decrease and brightness standards are also changing. Not long ago, 5,000 nits marked ideal brightness. These days 7,500+ nits is the expectation. On top of pixel pitch and brightness, the industry has come to expect additional capabilities like better uptime, cloud-based management and HDR color.

Last night, early Pixel 4 owners discovered that the Smooth Display’s 90Hz refresh rate is tied to screen brightness. Google confirmed and explained that decision today while promising a Pixel 4 Smooth Display update in the coming weeks.

The Smooth Display setting today “automatically raises the refresh rate from 60 to 90 Hz for some content.” Unlike the manual setting in Developer options, the main toggle does not consistently force the higher refresh rate in order to preserve battery life.

We constantly assess whether these parameters lead to the best overall user experience. We have previously planned updates that we’ll roll out in the coming weeks that include enabling 90hz in more brightness conditions.

Dell offers a Premium Panel Exchange that ensures zero bright pixel defects on Dell Consumer, Professional, UltraSharp, and Gaming including Alienware monitors.

Defective pixels do not necessarily impair the performance of the monitor. However,they can be distracting, especially if the pixels are in positions where viewing quality is reduced.

Unyielding commitment to quality and customer satisfaction has driven Dell to offer a Premium Panel Exchange as part of the standard limited hardware warranty. Even if one bright pixel is found, a free monitor exchange is supported during the limited hardware warranty period.

CTL display products are manufactured to rigorous standards. Our display products are consistently recognized as among the highest quality display products in the industry. Nevertheless, due to the nature of LCD technology, an LCD display may exhibit a small number of very small bright or dark spots on the screen. Often, these spots are noticeable only when the screen continuously displays a certain solid color such as an all-white or all black background. This type of background can be present when initially turning a computer on, or when a computer switches the display to a specific screen-saver.

Occasionally, these spots can seem to appear when a user switches to a different desktop background image. In actuality, these spots are pixels or sub-pixels that are stuck always on (viewable as a bright spot on a dark background) or always off (viewable as a dark spot on a light background).

An LCD display is made up of tens of thousands of individual pixels, and each pixel is made up of 3 individual sub-pixels (red, blue and green). In-fact, a 17" LCD has over 1,300,000 pixels and almost 4 million sub-pixels! Each sub-pixel is controlled by an individual transistor which turns the individual sub-pixel that it controls either on or off to create the image on your screen. An anomaly occurring during the manufacturing process can cause an individual transistor to continuously light or fail to light an individual pixel element, causing one of these small spots on the screen. Although this anomaly occurs relatively rarely in individual transistors, there are millions of sub-pixels on each LCD screen, and it is not uncommon for an LCD screen from any manufacturer to contain a few of these transistor anomalies and their associated bright or dark spots. For a manufacturer to sell only LCD""s with no transistor anomalies would result in a prohibitive cost to you, the consumer…one many times higher than it is today. Most people and applications are tolerant of a small number of these transistor anomalies on an LCD screen, and prefer the lower cost of LCD""s that existing standards allow.

CTL sets simple & strict limits as to the allowable number of non-performing pixels or sub-pixels on our LCD display and laptop computer screens. These criteria supplement our existing Warranty and are applicable during the warranty period for all CTL and 2go LCD displays as follows:

The LCD display of products under warranty will be replaced if CTL determines that it has 6 or more bright sub-pixels, 6 or more dark sub-pixels or a combination of 6 or more bright and dark sub pixels.

Please note that it is possible that any replacement display may also have some non-performing pixels or sub-pixels. This should be considered when requesting a warranty exchange.

CTL offers on certain models a No Dead Pixel Warranty.  A monitor purchased with this warranty will be replaced in the warranty period if one (1) or more dark or bight pixels are found.

Monitors already do report their maximum refresh rate to your PC. Your computer then generally sends new frames at this maximum refresh rate, whether new data is available or not.

In theory we could only send updates when pixel change, but in practice there isn"t much reason to do so. The whole hardware chain has to support updating every pixel on every frame all the time, so it"s highly efficient at doing so. This is a dedicated high-bandwidth link, so you"re not going to gain much at all by reducing the throughput across the link. In fact, you"d probably end up spending more money and energy on hardware to encode and decode the delta frames on each end of the link. It just makes more sense to send the whole frame each time. Especially for applications like games and movies, where 100% of the pixels are going to change every frame anyway.

As for your variable framerate idea, this is another can of worms. The entire display chain, from applications to the operating system to the graphics card through the monitor are built on the concept that updates happen at a fixed, pre-defined interval. Changing this to a variable interval would require that we throw all of that out. Furthermore, how do you decide what framerate to use at any given moment? Suppose your monitor can update at 100Hz maximum, and you open a 60fps video in a window. Does that then force everything else to update at the 60fps refresh rate even if it wants to update the monitor at 100Hz or 90Hz? If you"re updating a portion of the screen at 60fps, then you no longer have any evenly-divisible time slices in which to do your 100Hz equivalent updates.