Welcome to Exploring Computing.
Today's video is Digital Images Part 1, The Basics.
In this video, we're going to take a look at how a computer
display works.
We'll also take a look at some different aspects of computer
displays and televisions.
And so these might be useful if you
were to go shopping for a new computer or new television.
The next video, we'll take a very close look
at how color is generated.
For now, even though some of the examples I have
will use color images, we're going
to defer the discussion of how the color actually
works until the next video.
Let's start off by taking a look at a typical computer screen.
If we take a look at a computer screen,
and we get a magnifying glass in order
to look very closely at the screen, what we'll discover
is that the screen is actually composed of a gigantic grid.
In a black and white case, each of the grid elements
can either be on or off.
And by turning individual pixels on or off,
we can actually generate a particular image.
So in this case, I've turned on a number of pixels
in the top left hand corner, and you
can see that this is forming the letter
H. Each of these individual grid element
is what we refer to as a picture element or, for short, pixel.
In the black and white case, each pixel
is backed by an individual bit somewhere in computer memory,
and if that bit is on, then the corresponding pixel is on.
And if that bit is off, then the corresponding pixel is off.
One thing that you might want to look at when you're considering
purchasing a computer or a television
is the screen resolution.
The screen resolution is how many pixels wide
and how many pixels tall a particular display is.
Here are some sample screen resolutions.
A Surface Book 15 inches, 2,496 pixels across,
and 1,664 pixels down.
A MacBook Pro 15 inches, 3,072 pixels from left to right
and 1,920 pixels from top to bottom.
Here's an interesting example that a friend of mine
purchased.
This is a 34 inch ultra wide monitor.
It is 3,440 pixels wide by 1,440 pixels tall.
And then finally, here's a 55 inch high definition
television.
It is 1,920 pixels wide and 1,080 pixels tall.
Some of these different screen resolutions
have names that you may occasionally hear.
So for example, one of the older resolutions is 640 by 480.
This is used both by older computers and older
televisions.
I mention this because 640 by 480 for computers
was referred to as VGA.
And you will still hear this name occasionally,
usually in conjunction with connectors for monitors that
were used back in the VGA days, and in fact, they're
still in use today.
Many classrooms at Stanford still have VGA connections,
and here's a photograph showing you
what a VGA cable looks like.
For televisions, the same resolution 640 by 480
is referred to as 480i or 480p.
We'll be talking in the next video
about what the i and the p actually stands for.
That 3,440 by 1,440 pixel monitor,
that's referred to as an ultra wide.
And then here's another one that you will commonly hear.
1,920 pixels by 1,080 pixels is referred
to as HDTV for high definition television,
or it's sometimes referred to as 1080p.
One important quality to consider
when we're looking at a monitor or television
is the aspect ratio.
The aspect ratio is the ratio between the width
of the display and the height of the display in pixels.
When we're talking about computer displays
or televisions, this is always given
as a ratio of two whole numbers.
So what we're going to do is, we're
going to take the number of pixels
wide and the number of pixels tall
and try and come up with the smallest
pair of integer numbers that gives us the exact same ratio.
Let's take a look at an example.
Here we have a model that's 1,024 pixels wide and 768
pixels tall.
If we want to come up with the lowest possible integer
numbers, giving us the same relationship
between the width and the height,
it turns out if we take the 1,024,
and we divide it by the 256, that's
going to give us the integer number 4.
And if we take the 768, and we divide it by the 256,
that gives us the integer number 3.
And so we would say that this particular display is a 4
by 3 display.
To use another example, if we take
a look at our 1,920 by 1,080 high definition television,
and again, looking for the smallest pair of integer
numbers that gives us the exact same ratio, what we would do
is we take the 1,920, we divide it by 120,
and that would give us 16.
And we would take the 1,080 and divide that by the same 120,
and that would give us the integer 9.
And so we would say that the aspect ratio of an HD
television is 16 by 9.
Now notice, while these aspect ratios
are directly related to the screen resolution,
they are not the same.
Here we see three different displays
that all have the same 4 to 3 aspect ratio,
and yet, we can see that they have wildly different numbers
of pixels.
The largest box represents a 27 inch old school CRT television,
which would be 640 pixels by 480 pixels.
And we also see a 12.9 inch iPad Pro.
This has many, many more pixels, 2,732 by 2,048.
And then finally, we have a 7.9 inch iPad
Mini, which is 2,048 by 1,536.
All three of these, if you work them out, are 4 by 3.
And yet the number of pixels is quite different.
And you can actually see that the number of pixels
is not directly related to the size of the screens.
We'll be talking about that a little bit later.
So what's the best aspect ratio?
Well, it actually depends on what
you're planning to use the device for
and how large the device is.
Let's first take a look at what sort of device
we might want to use if we're trying to get some work done.
Here's a large 27 inch 16 by 9 monitor.
You can see that with this monitor, it's quite wide,
and we can very comfortably see two documents side by side.
So for work purposes, a wide screen large monitor
works really, really well.
On the other hand, let's take a quick look
at a comparison between two different tablets.
Our tablet on the left is a Samsung Galaxy Tab S4.
This is a 16 by 10.
And on the right, we have an iPad Pro.
You can see with the iPad Pro, we
can actually see it a fair amount more of the document.
And in fact, the Samsung Galaxy Tab
is a 16 by 10 instead of a 16 by 9.
They used to make 16 by 9 tablets,
but they were so short, that people just couldn't
get much work done on them.
And so they have moved to 16 by 10.
But you can see from this image here,
this comparison here, that the iPad's 4 by 3 ratio
does get us more of a document.
So if we're interested in viewing documents
on our small screen tablet, you know, that 16 by 9 widescreen
is not necessarily the best choice.
On the other hand, if we're interested in entertainment,
for most types of entertainment the 16 by 10 or 16 by 9
is going to work really great.
Let's take a look at that next.
So what we're going to do now is we're
going to take a look at our 16 by 9 and our 4 by 3 screen
ratios.
Let's say we've got a small size 4 by 3 iPad,
and we've got a large screen 16 by 9 HDTV.
Now, when we're looking at movies and television,
they also have aspect ratio.
And so ideally, what we'd like is the aspect ratio
of our screen to match the aspect ratio of our film
or television.
Now, there's a couple of things you need to know.
First of all, the aspect ratios given in film and television
do not use whole integers.
Instead they use decimal numbers.
So for example, instead of having 4 by 3 or 16 by 9,
we might get something like 2.35 to 1 or 1.85 to 1.
So they actually use those decimals.
The other thing is we need to know
what happens when the aspect ratio of our device
does not meet the aspect ratio of our media.
And what's going to happen is we're either
going to get a letter box, which means that the media will
occupy the center of our screen, and then above
and below that media we'll get black bars.
Or we'll get pillar box, which means that the media will,
again, occupy the center of our screen,
and on the left and the right we're going to get black bars.
So this is what's going to happen when things don't match.
Let's start off with an action movie Captain America--
Civil War.
Now, action movies really like taking full advantage
of a wide screen.
And so we're going to see that action movies have
very wide aspect ratios and are going
to have large amounts of letter box on the top and bottom.
So for our HDTV, HDTV is already pretty wide,
so the letter box above and below, those black bars above
and below aren't that big.
But they are still present.
In contrast, with the iPad, you can
see that there are much, much thicker black bars on the top
and bottom.
And that's because the aspect ratio of the iPad
does not match Captain America's aspect ratio nearly as well
as the HDTV does.
Here's another action movie.
This is the Fellowship of the Ring from 2001.
This has the same aspect ratio as Captain America,
or roughly the same aspect ratio as Captain America.
Both of these, and most action movies,
are somewhere around 2.35 to 1.
And again, it's a bit wider than even our wide screen
televisions.
In contrast, if we look at dramas,
these actually are quite close to our HDTV standard.
This is Sense and Sensibility from 1996.
This is 1.85 to 1, and this matches almost perfectly
with our wide screen television.
So if you've got a widescreen television,
and you're watching a drama like Sense and Sensibility,
it's going to fit just about perfectly.
In contrast on our iPad, again, we
can still see the black bars on the top and the bottom.
This is Up from Pixar 2009.
Again, very similar, same aspect ratio as Sense and Sensibility.
So these dramas are going to look really great on an HD
Television.
There's not going to be any letterboxing at all.
We will get a bit of letterboxing on an iPad.
Now, earlier I talked about how the Samsung Galaxy Tab didn't
work quite as well as the iPad's 4
by 3 ratio for getting actual work done
and reading documents.
Well, this would work perfectly for these movies.
So if you're buying a tablet to watch media, then the 16 by 10
would work great.
If you're buying a tablet to get work done, then maybe
the 4 by 3 iPad ratio works better.
Finally, let's take a look at some older media.
This is the Friends television show from the 1990s.
This has a 4 by 3 ratio, so this fits perfectly on our iPad.
But when we place it on an HD television, it doesn't fit.
So what's going to happen is, we're
going to have to place black bars on the left and the right.
And again, this is sometimes referred to as pillar box.
And then finally, if we have an old school movie,
like say the Wizard of Oz from 1939 or Casablanca from 1943,
these are going to be very similar to Friends.
These have a 1.37 to 1 ratio, whereas Friends has a 1.33 to 1
ratio.
But it's just about the same, and it's
going to fit perfectly or almost perfectly on our 4 by 3 iPad.
But again, with our HD television,
we're going to have to have those pillar
bars on the right and the left.
All right, our next video is going
to take a look at how computers generate color.