Oct 012015
 
Modern tablets come in all shapes and sizes, starting as big phones and ending as medium sized laptops.

Modern tablets come in all shapes and sizes, starting as big phones and ending as medium sized laptops.

Perhaps the most important part of a tablet is its screen.  It is simultaneously your input and output device, and nearly everything you use a tablet for revolves around its screen.

There is a lot of confusion about what makes a screen good or bad, and how to compare two different screens to understand their relative strengths and weaknesses.  Furthermore, whenever we encounter a bargain priced tablet, invariably the component that the manufacturer has made the biggest quality compromises on is the screen.

So, next time you’re considering a tablet, here’s what you need to know in order to understand if you’re getting a ‘good’ or ‘bad’ screen.

Screen Size

You might think that bigger is always better.  Certainly, when it comes to watching video, bigger is usually better.  But for other purposes, the chances are you get to a point where making the screen larger starts to represent too much of a trade-off in terms of cost and size and weight.

The more portable you wish your tablet to be, the more important it becomes to keep some control over the size/weight of the device, and cost is always a factor to consider, too.

From a purely definitional point of view, it seems that the smallest screen you can expect to find on a tablet is probably a 6″ diagonal.  Anything smaller than that and you’re instead looking at large screened phones, or ‘phablets’ – cross-over devices that can’t quite device if they are a tablet or a phone.

At the other end of screen sizes, it is rare to find tablets with larger than about 12.5″ on their diagonal.  Apple’s new iPad Pro has a 12.9″ screen and Microsoft’s Surface Pro 3 has a 12″ screen.

Most screens are clustered in the 7″ to 10″ range.  That might seem like a relatively small range of screen sizes, but diagonal measurements are deceptive.  There’s more than twice as much screen area on a 10″ diagonal screen as there is on a 7″ diagonal.

Which brings us to the next point.

How to Measure Screen Size

You might think this to be a ridiculous question to ask.  Use a ruler, you say.  If only it were that simple!

Historically, screens on televisions and computer monitors have always been measured by their diagonal size – this being quick and easy, because all screens had the same aspect ratio – the same proportion between height and width.  So instead of quoting two measurements for height and width, it was easier to quote just one – oh yes, and the fact that the single number for the diagonal was larger than either of the other two numbers was probably viewed by the marketing people as an extra plus, too!

Early screens were also not completely square, which made it harder to measure the square inches of screen area.  So a simple diagonal measurement was used everywhere.

This measurement continued into phones, although the screen sizes were so small (to start with) that a more important/relevant measure was often the screen’s resolution in pixels rather than size.

When the first modern tablet – the iPad – was released, Apple chose to describe it in screen diagonal terms too (9.7″), although it was no longer an unambiguous measurement, because computer screens were changing from always being in the same aspect ratio/proportion, to coming out with assorted new shapes – wider than before.

Since then, there has been a ‘free for all’ in terms of screen aspect ratios (see below for a discussion on how much screen area is actually used), and the diagonal measurement no longer really tells you much at all.  But, in an industry obsessed with change and leading edge innovation, the historical screen measurement has remained unchanged, even though it is now of much less value.  Depending on the aspect ratios, a screen with a larger diagonal measurement than a different screen with a smaller diagonal measurement might actually have fewer square inches of screen area (and more, less, or the same number of pixels – another whole topic we discuss, below).

There’s another problem with using diagonals to express screen size.  As mentioned above, and assuming the same proportions on both screens, a 10″ diagonal screen has about 2.2 times as many square inches of screen area as does a 7″ diagonal screen, even though there’s only a 50% increase in diagonal measurement.  The change in diagonal measurement has a much larger impact on total screen size than you’d think.

So how should you measure screen size?  We suggest two relevant measures.  The most easily grasped one is to quote the number of square inches of screen area.  A slightly more abstract one is to understand the actual width and height of the screen, rather than just the diagonal.

Unfortunately, these numbers are seldom provided, but can usually be calculated by dividing the screen resolution measurements by the PPI density.  For example, a 1920 x 1080 screen with a 350 pixel per inch density would have dimensions of 5.5″ x 3.1″.  Multiply those to determine an area of 16.9 sq inches.  (The diagonal on this example would be 6.3″, in case you were wondering.)

Screen Resolution

More pixels are usually better than less pixels, but there comes a point of vanishing returns where you can’t actually see any improvement in display quality by cramming more pixels onto the screen.

Tablets invariably describe the pixels on their screen in terms of how many pixels there are horizontally and vertically.  That is good to know, and there are some minimums you don’t want to go below.

In terms of absolute pixel counts, it is rare these days to see any tablet with a resolution of less than 1024 x 600; indeed, if you encounter a device with fewer pixels, don’t buy it.

There are advantages to increase the pixel count to 1280 x 720, and then lesser advantages to keep growing it to 1920 x 1080, and then you start to tail off from that point with increasingly smaller benefit attached to more pixels.

The importance of the numbers quoted in the preceding paragraph is that 720P video uses 1280 x 720 pixels, so anything of that size or larger enables full 720P type HD video to be shown with no loss of picture information.  The 1920 x 1080 number represents the ‘full’ 1080P resolution, so if your screen has that many pixels, you can get the added picture information contained in this format.

To put this all in context, a DVD typically offers 720 x 480 pixel resolution, and it is only a few years ago that they were thought to be of stunning high quality!

Any resolution video can display on any resolution screen, but if there are fewer pixels on the screen than in the video feed, you’re going to be losing picture information.  There won’t be as much fine detail and clarity as if there were at least as many pixels on the screen as in the feed.

But there’s another factor as well.  Not just the total pixel count, but how close together (or far apart) they are.  Which leads to :

Screen Pixel Density

Now for an interesting point.  You can have three screens with the exact same number of pixels, but one looks very much better than the other two.  To take an extreme example, lets say you have 3″, 6″ and 12″ screens, all with a 1800 x 1200 pixel count.

The 6″ screen would look mirror sharp and you could see the picture very clearly indeed, even if you got really close to the screen.  The 3″ screen would also be very sharp, but unless you got a magnifying glass, it would simply be too small for you to clearly distinguish all the detail in the picture.

At the other end, the 12″ screen would look grainy.  You could see the individual dots in the picture, and instead of smooth lines, you’d see slightly jagged edges.  To look as good as the 6″ screen, you’d find yourself holding the screen further away from you, and that begs the question – if you’re having to hold the 12″ screen uncomfortably far away, why not get the cheaper 6″ screen and hold it normally?  (The answer to that question – if you are wanting to make a presentation to several people at the same time, they will necessarily be a bit further from the screen, so the larger size is useful then, even if not so useful as a personal device.)

What you’ve just experienced in this thought experiment is the concept of pixel density compared to total pixels and screen size.  Pixel density, measured in pixels per inch (PPI) tells you how ‘sharp’ the image will be.

Opinions vary widely, as does the ‘science’ used to ‘prove’ the opinions, but in round figures, it is fair to say that anything with much more than about 300 pixels per inch starts to get so fine-grained that we can’t see any extra detail, even at quite close distances.  Once you start to go over 400 ppi, you are definitely into the realm of vanishing returns and are unlikely to see much improvement in picture quality.  Perhaps surprisingly, one of the most demanding visual uses for a tablet is to display text, because of the very thin lines in normal text and the subtle varying thicknesses in the more readable (weighted with serif) fonts.  We’d be happy to see 400 ppi used for text, which is starting to get in the same territory as laser printers.  But for photos and video, 300 ppi is plenty.

How many ppi is too few?  That depends on how close you’ll be looking at the screen.  For example, look at your television set.  For example, I’ve a large 75″ diagonal set that gives a brilliant sharp picture.  But it has a mere 30 ppi count.  However, I watch the tv from across the room, so that is okay.

A regular computer monitor used to have in the order of 70 – 75 ppi, and these days probably has 90 – 110 ppi, but again, we look at these usually from a larger distance than a tablet, and also, for historical reasons, have come to instinctively accept poorer quality images on a computer monitor than we expect on a tablet.

Another example to help put things in perspective – the original iPads, when they came out in early 2010, had 132 ppi on their screens, and no-one complained, at the time, of them as being anything other than amazing!  (Modern iPads have 264 ppi.)

So, rule of thumb time again.  For a tablet, and noting how standards have improved since the iPad launched, we’ll arbitrarily say that you should expect a minimum of 150 ppi, and can consider anything over 225 ppi as very good, anything over 300 ppi as excellent, and anything over 400 ppi as wasted.

How Much Screen is Actually Used?

Some apps on a tablet will flow to fill your screen, no matter what its shape and size.  Others are defined and fixed in size.

As you surely know, you can vary the width and depth of a window to view a web page in, and these days modern web pages semi-automatically vary how they present their material to take best advantage of the page width available to them.  You can use all your screen when viewing web pages, no matter what its size and shape.

But some other applications rely on a certain proportion between the height and width of the screen.  This is obviously true when viewing photos – photos direct from a camera are sometimes in a ratio of 1.5:1, sometimes they are almost square (1:1), and sometimes wider than 1.5:1; and after they have been cropped, might have any size and shape at all.

Probably the most important aspect ratio consideration is if you are wanting to watch video on your screen.  Old movies (think black and white) and television programs until the last decade or so were all filmed in what is called ‘Academy’ format; a 4:3 or 1.33:1 aspect ratio.

Movies then started becoming wider and wider, and growing to as much as a 2.5:1 aspect ratio before settling back to typically in a range between about 1.85:1 to 2.39:1.  HDTV uses a 16:9 or 1.78:1 ratio.

If the aspect ratio of the video you are watching is not the same as the aspect ratio of the screen, you’ll end up with black bars, either above and below the video if the video is wider than your screen, or on either side if it is squarer.  A typical modern tablet with perhaps a 1.65:1 ratio would have side bars for older tv programs and top and bottom bars for modern wide screen movies.

So which is the ‘best’ aspect ratio for a tablet?  Is Apple correct with its 1.33:1 ratio?  Or are other companies, with their preference for wider screens, offering better choices?

It depends on the main use you’ll have for the tablet, and also on its size.  The smaller the tablet, the more precious each square inch of screen area becomes.  The larger, the more readily you can afford to ‘lose’ a bit of screen space for some applications.

If watching movies and relatively modern tv shows is going to be a significant part of your tablet usage, and if you’re looking for a smaller tablet, then we’d suggest getting a wider screened tablet, perhaps 1.6:1 or greater.  But if you’re considering a 10″ or larger tablet, then its aspect ratio isn’t quite as essential, and a 1.33:1 ratio would be fine.

How Much Screen Do You Need?

As we started off by saying, the answer to this question unavoidably requires you to trade-off between screen size (bigger is better) and the unavoidable correlating factors – weight (less is better), overall tablet size (smaller is better) and cost (ummm, you can probably work that one out for yourself!).

To look at the extremes, it is probably obvious that a 6″ diagonal screen is better than a 3″ screen, and a 25″ diagonal screen is clearly a ridiculous size for a tablet.  Where in the middle is the perfect size?  Is there even such a thing as the perfect size?

Steve Jobs famously claimed, when launching the iPad, that there was indeed a perfect size for a tablet, which of course was the 9.7″ of the iPad he was releasing that day.  But the 9.7″ iPad has seen its market share go steadily down and down, losing out to tablets of all different other screen sizes, and Apple itself, after Jobs’ death, first released a smaller 7.9″ screen iPad Mini, and now are releasing a larger 12.9″ iPad Pro.  Apple itself no longer believes there’s one perfect size, and noting how the iPad Mini is thought to be selling in approximately equal numbers as the regular iPad, the market seems to agree.

Here is an interesting test for you to put size into perspective.  Sit at the most comfortable distance from your normal computer monitor, and then hold up a tablet at its typical viewing distance and have it block the computer monitor.  Is the tablet’s screen (not the larger bezel around it) blocking more than the computer screen, or less than the computer screen, or about the same (or at least that part of the screen on which you typically have a normal sized window residing – my very big screens have multiple windows on them, you probably do the same thing)?  Repeat the test, this time sitting at what would be an ideal distance from your television (assuming it to be an HD tv).  Which takes up more viewing area this time – the tv or the tablet?

If you want to do a third test, compare the tablet screen to a typical page in a typical book.  Although this is less important, it makes some small amount of sense to expect the tablet screen to be similar in size (or perhaps larger) than the print areas in the book (after eliminating much of the margins on the page, which are sort of similar to the bezel around the tablet screen).

If you haven’t already bought a tablet, you can still do these experiments by cutting out some pieces of cardboard for the screen sizes of tablets you are considering.

If the tablet is consistently larger than your computer monitor and television screen and the books you read, then it is clearly sufficiently big for most purposes.  If it is appreciably smaller, then you’re going to be experiencing some compromises.

This is only one measure and one factor, but might help put screen sizes in perspective.

In general terms, we think the sweet spot is in the 8″ to 10″ range.  7″ devices are okay, but are going down to the far end of acceptable, and larger than 10″ devices are great, but the trade-offs start to become appreciable factors.  At the limits, a 6″ device these days is more like a large phone than a tablet, and a 14″ device is more like a laptop than a tablet.

There are trends that will move the ‘sweet spot’ upwards in size over time.  Bezel sizes can reduce, making more of the overall tablet size as screen and less as waste space.  Weight and thickness will continue to reduce, reducing those limitations.  Better manufacturing techniques will make it possible to make bigger screens with the necessary extraordinary number of pixels on them at affordable prices, and faster CPUs and GPUs will drive them.  Improvements to both Android and iOS are already starting to allow multiple programs to be in separate simultaneous windows on the screen, which is a huge driver for ‘needing’ more screen space.

So we expect and eagerly look forward to continued growth in tablet screen sizes.

Summary

We suggest you select tablets with at least a 7″ screen, a 1024 x 600 resolution, and a 150 ppi density.  Another inch or two of screen would be nice, an increase of resolution to more than 1280 x 720, and greater density to something over 200 ppi would also both be good.

The ideal screen is probably very close to the 9.7″ claimed by Steve Jobs, and the tradeoffs associated with larger screens are currently limiting factors as you start to grow above that size.

  One Response to “Making Sense of Screen Specifications on a Tablet”

  1. […] We suggest the considerations for most of us to give prominence to are screen size/resolution and cost.  The screen size/resolution issue is actually quite layered in its complexities, and so we published an article just now all about how to evaluate tablet screen size issues. […]

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