Tablets have to balance portability and usability. With the display being the primary interface for the device, this is going to be one of the most important features that will determine much of the rest of the tablet. Because of this, consumers must learn a good amount about the screens to make an informed buying decision. Below are some of the things to consider about the screen when looking at tablet PCs.
The screen size is going to primarily impact the overall size of the tablet PC. The larger the screen, the larger the tablet will be. Most manufacturers have decided to standardize on one of two rough display sizes. The larger of these are around 10-inches in size which are a little less portable but offer greater battery life and easier to read screens. The smaller tablets use 7-inch displays that offer greater portability but can be more difficult to read and use. There are a number of tablets with screen sizes between these two making the 7 to 10-inch the most common range. Having said this, there are some available with screens as small as 5-inches while some tablet based all-in-one systems have upwards of 20-inches.
The aspect ratio of the display is another thing to consider. There are two primary aspect ratios used in tablets right now. Most use the 16:10 aspect ratio that was common to many of the early widescreen computer displays. This isn't quite as wide as an TV's 16:9 aspect ratio but very close. This makes them very useful in landscape mode and for viewing HD media. On the downside, the wide display can make the tablets very top heavy when being used in portrait mode often used for reading ebooks or browsing some web sites. The other aspect ratio used is the traditional 4:3. This gives the tablet a feel more like a standard pad of paper. It sacrifices the wide display in landscape mode for viewing video for a more balanced tablet and is easier to use in portrait mode.
The resolution of the screen also plays an important role in the display of a tablet. Higher resolutions will mean that it can display more information or detail on the screen at a given time. This can make watching a movie or reading a website easier to do. There is a downside to high resolution though. If the resolution is very high on a small display, it can become difficult to read the resulting small text. In addition, it also becomes much more difficult to precisely touch the screen in the spot you want. Because of this, one has to look at the resolution as well as the screen size. Below is a list of the common resolutions found on most tablets:
- WVGA: 800x600
- WSVGA: 1024x600
- XGA: 1024x768
- WXGA: 1280x800 or 1366x768
- WXGA+: 1440x900
- WSXGA+: 1600x900
- WUXGA: 1920x1080 or 1920x1200
- QXGA: 2048x1536
- WQHD: 2560x1440 or 2560x1600
- UHD: 3180x2160
Now resolution is also important for those watching media as well. Typically, high definition video comes in 720p or 1080p format. 1080p video typically can't be fully displayed on many tablets but some can output video to an HDTV via HDMI cables and adapters. They can also scale down a 1080p source to be viewed at a lower resolution. In order to view the lower 720p HD video, it is necessary to have at least 720 vertical lines of resolution in landscape mode. In addition, if it is widescreen content like most HD video is, it really should have 1280 horizontal lines or more in landscape mode. Of course, this only really matters when trying to watch it at full 720p resolutions.
Pixel Density or PPI
This is the latest marketing blitz by manufacturers to try and highlight the clarity of their screens. Essential, pixel density refers to how many pixels are on the screen per inch or PPI. Now the higher the number, the smoother the images on the screen will generally be. Take two different screen sizes, one seven inches and the other ten inches, both with the same native resolution. The smaller screen will have a higher pixel density which means a sharper image even though both display the same overall image. The problem is that at a certain point, the human eye typically can't distinguish any more detail. Many of the new screens have PPI numbers between 200 and 250. At the typical viewing distances, this is generally considered as detailed as a printed book. Beyond this level, consumers generally won't be able to tell the difference unless they move the tablet closer to their eyes which can make them more difficult to read or hold for extended periods of time.
At this point, manufacturers are not advertising the viewing angles of the displays on tablet PCs but this is something that will be very important. Just the fact that they can be viewed in portrait or landscape modes means they have to have wider viewing angles than a laptop or desktop display. If a screen has poor viewing angles, adjusting either the tablet or the viewer to get a proper image can make the tablet very difficult to use. Tablets are generally held in the hand but it is possible to put them on a flat table or a stand as which can limit the ability to adjust the angle of viewing. They should have very wide viewing angles that allow them to be viewed properly from just about any angle. This not only makes them easier to hold but it also allows them to be viewed by multiple people.
There are two things to look at when testing a tablet's viewing angles: color shift and brightness or contrast dropoff. Color shift is noticed by the colors changing from their natural color when the tablet is shifted off a straight on viewing angle. This can be seen as a single color like green, blue or red turning dark while the others remain natural. Brightness or contrast dropoff is noticed when the entire image becomes dimmer. The colors are still there, just darker all around. The best tablet displays should remain bright enough without color shift at the widest range of angles.
The way that an LCD screen works is that you have light behind the screen that is put through polarized fitlers for the various red, green and blue subpixels. This helps to generate the image with all its color rather than just a bright white screen. Now the polarization itself is not a problem but the angle of the polarization can have implications if you intend to view or use the tablet while wearing polarized sunglasses. You seen, if the angle of polarization on the tablet screen line up perpendicular to the polarization angle of the sungless, you end up blocking out all the light from the screen and it appears black.
So why am I bringing this up? Well, the polarization problem that causes the screen to black out only happens at one particular angle. What this means though is that if you intend to use the tablet while wearing sunglasses, you will only be able to see the display well in one orientation, portait or landscape. This could impact how you use the tablet. For instance, if you like watching widescreen video but the orientation places it in portait mode or you like reading books but you need to view it in landscape mode, then you might end up using it in a way you dislike. It is not a major issue, but something to be aware of if you are going to compare several tablets in person.
Coatings and Brightness
Finally, users will need to consider how the display for the tablet PC is coated as well as the brightness levels it can achieve. At this point, pretty much every tablet is using some form of hardened glass coating over the display such as Gorilla Glass. This does a great job of protecting the display and can really let the colors stand out but they are highly reflective that can make them difficult to use in certain light such as outdoors. This is where the brightness of the tablet also comes into play. The best way to overcome the glare and reflections is to have a display that can be bright. If a tablet has a glossy display and a low brightness, it can be extremely difficult to use outdoors in bright sunlight or in rooms where a comfortable viewing angle causes reflections from light fixtures. The downside to extremely bright displays is that they tend to shorten the battery life.
Because the interface is also built into the display, the coating on the tablet PC is going to get dirty and quickly when it is used with one's fingers. All tablet displays should have a coating that allows them to be easily cleaned by a standard cloth without the need for special cleaners or fabrics. Since most use a form of glass, this isn't much of a problem. If a tablet does come with an anti-glare display though, be sure to look into what can be used for cleaning it before purchasing one.
The color gamut refers to the number of colors that a display is able to produce. The larger the color gamut the more colors it can display. For many people, the color gamut is going to be a very minor issue. This is really only going to matter for users that will use their tablets for editing of graphics or video for production purposes. Since this isn't a common task right now, most companies do not list what the color gamuts for their tablet displays are. Eventually, more and more tablets will likely advertise their color support as this becomes more important to consumers.