Guide to iPad and other Tablet Devices : Part 2
Screen Issues - one of the most
important and widely varying factors in different tablet
The amazing Kno tablet,
possibly to be released prior to year end, will be available
with dual 14.1" screens.
This represents perhaps
the upper limit of screen size on a tablet.
Perhaps the most most important
part of any tablet device's hardware is its screen.
This is the primary output
medium for everything it does, and also the primary input medium
An awkward tradeoff is required
between the 'bigger is always better' screen concept we can
embrace when buying a screen for our desktop computer, and the
'tablet devices are convenient, portable, and lightweight'
constraints surrounding any tablet.
This part of our iPad/Tablet
Buyer's Guide walks you through the different options and
implications of screen choices on tablet computers.
The screen is the main part
of a tablet device, something you'll use both for input and
output to/from the tablet. It is possibly also the part of
a tablet which currently shows the greatest variation from one
product to another, and you need to understand the implications
of the different approaches and the compromises inherent in each
Screen size/aspect ratio
Screens are typically measured by
quoting the diagonal size of the screen. This used to make sense
when all screens were of the same aspect ratio (ie the ratio
between the screen's width and height - formerly most commonly
4:3 like an old fashioned television, these days often something
around about 16:10 or 16:9 like a new widescreen television) but
with differing aspect ratios, the diagonal size alone is no
longer so meaningful.
Quick rule of thumb : A wider screen will have a larger diagonal
measurement for the same number of square inches of screen that
does a 4:3 aspect screen. In other words, wide screens overstate
their size when only measured by diagonal.
The range of screen sizes for tablets currently seems to range
from a low of about 5" (usually a widescreen format screen) to a
high of 9.7" (Apple's current 4:3 ratio iPad screen),
although some less well known devices such as the Kno tablet are
pushing this number up to somewhat ridiculous sizes - 14.1" and
optionally with dual 14.1" screens).
probably represent the upper and lower limits for what makes
sense in a tablet screen. At 5", you have a small screen that
makes it harder to read web pages or to enjoy video; at 10",
you have a big screen that unavoidably is starting to become
less portable to carry
and too heavy to hold.
We'd suggest the sweet-spot is something bigger than 6", and
potentially all the way to 9.7" as long as you realize the
sacrifices and trade-offs you'll be making if you go to the very
large screen size.
Which is better - widescreen or regular aspect ratio screens?
There is no real answer to
that, because it depends a lot on your primary uses for the
If you're mainly going to be
using the tablet to watch movies, then you'll probably find a
widescreen style screen is better suited.
But if you're going to be
using the tablet most of the time to surf the internet, you'll
probably find the standard aspect screen is more useful,
allowing you to get more of a web page conveniently visible on
the screen at a time.
The other big issue is how
many pixels the screen contains. In general, the more
pixels you can get on your screen, the better the quality the
image you'll see, allowing you to have smoother letters in small
fonts, and higher quality on pictures and video.
There is an upper limit to
how many pixels you can benefit from. Apple sort of
determined the limit on how many pixels per inch your eye can
conveniently resolve, and claims it to be in the order of about
300 pixels/inch, although this number embodies an assumption
about how close to the screen your eyes are. Their new
iPhone 4 boasts 326 pixels/inch (ppi) (ie 960x640 pixels total
on the 3.5" display). In comparison, their iPad has 132
ppi (1024 x 768 pixels on a 9.7" display). A regular
computer monitor will commonly have anywhere from about 70 to
If two screens are of
different sizes, but with the same number of pixels resolution,
you won't see more image or detail on the bigger screen, and
neither will you see less image or detail on the smaller screen.
Assuming that the smaller screen with the higher pixel density
isn't going up above 300 ppi, you'll see as much on the smaller
screen as on the bigger screen, and indeed, if the pixel
resolution drops much below 75 ppi, the image on the larger
screen will start to seem coarse and rough rather than smooth
On the other hand, if you
have two screens of the same size, but with differing numbers of
pixels, you will see more and better information on the screen
with the greater number of pixels. The limiting point here
is when things get too small to be clearly seen by the unaided
eye at regular viewing distances, no matter how many pixels go
into making them up.
One limiting factor on the
benefit of more pixels applies to video. Standard quality
video (eg on a DVD) has no more than 720x480 pixels of
information per frame. Most/all tablets already have at
least that many pixels, although many cell phones and MP3
players don't, so for regular quality video, you'll get no
improvement in picture quality by adding more pixels to the
It is true that HD video can
have 720x1280 pixel resolution (for 720p) or even a larger
1080x1920 pixel resolution (for 1080p and 1080i) and in such
cases, obviously more pixels up to these maximums will allow for
more picture information to be shown and the quality to
But you will probably never
choose to watch true High Definition video on your tablet, no
matter what the advertising might suggest. Why?
Because it will use up way too much storage. A good
quality video might use about 1GB per hour of programming, but a
true high quality video can go up to (and over) 10GB per hour.
That is fine when you're
watching video from a Blu-ray disc with a 50GB capacity, and
where you have a library of discs on your bookshelf stretching
several feet, but when you have a 32GB iPad (that also lacks
sufficient pixels to display the image correctly anyway) you'd
end up with only enough storage for a single movie to be on the
unit at a time - not much use if you're on a 10 hour plane ride.
In other words, and to try
and tie these issues together, more pixels are nearly always
better than fewer pixels, and it is usually preferable to have
more pixels on a same size screen than a bigger screen with the
Don't accept any tablet with
less than 800x480 resolution, and try and hold out for something
larger than this.
Visibility in bright light
This is the Achilles heel of
many LCD screen devices. In bright sunlight, they 'wash
out' and it gets very hard to see whatever is on the screen.
Some screen technologies are
better than others in terms of displaying a clear image in
bright sunlight. If you expect to be using your tablet
outdoors in places with bright sunlight, you should factor this
into your calculation.
of a multi part Buyers Guide to iPad/tablet devices.
Please visit the other parts of this series - links at the
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30 Sep 2010, last update
21 Jul 2020
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