- [Instructor] There are great reasons
to use one version or another of YUV,
so why don't we use it for everything?
Well, for one reason, when the specifications
were devised for the various forms of YUV,
it was given a smaller range of colors
than RGB systems can reach.
And in practice, if you compare one to the other,
you lose something in the region of 10%
of the available colors.
That's colors your eyes could see if they were shown.
There are different kinds of YUV
for different video systems,
and this is discussed in the lesson on legal levels.
There's an argument, actually, to use RGB for everything,
but we don't do that partly because of our history
of using YUV for camera image acquisition and display.
Regular TV screens display in YUV color.
So computer screens use a form of RGB called sRGB,
TVs use YUV, and digital system screens
use another form of RGB altogether.
These are all ways of describing the amounts of each color.
So this much red is this number, for example,
is all they're doing.
As long as we all agree the number means that much red,
the number can be used by cameras, computers, and displays.
The only way to know which system to work with
is to know how you images will ultimately be displayed.
So professional grading artists
literally have each kind of screen available
to check the image,
and it's common for major films
to be produced in different versions
for different forms of distribution.
Literally a different copy of the same film
with the colors carefully prepared
for each kind of display.
This is a pretty long explanation, isn't it?
But the good news is
you don't need to worry about it too much.
Just know if you're working in YUV or RGB.
Know that there's a difference
and that moving between the two
means either chopping off about 5% of the colors
at the darkest and brightest ends,
or seeing the brightest or darkest parts of your image
as a little bit gray
rather than the perfect black or perfect white.
Let's take a moment to look at why that is.
Here's RGB with a scale from zero to 255.
Now, against that same scale, here's YUV.
On the same scale, YUV goes from 16 to 235.
It's very likely that you'll have seen these numbers
at some point in software.
Because YUV is a shorter range than RGB,
it can lead to some problems.
Let's say you're producing video for television broadcast,
and you're editing with a computer screen
that's displaying color in the larger sRGB scale.
Now, let's say you're using
a non-linear editing system to edit
that also works in RGB color,
which is definitely the norm.
It's important in a scenario like this
to have a TV monitor connected to your system,
so you can see the way the colors will ultimately appear.
Very bright detail, like clouds in the sky on a sunny day,
could easily be chopped off
when the signal's displayed on the TV.
The problem is simply that the image
won't be squeezed into the new scale.
Details that don't fit become pure white or pure black,
and that lovely sky you included in your film
might look very plain when displayed on a TV screen.
This problem works the other way, too.
If you finish a video
with the color intended for YUV screens,
when you view that on a computer monitor
the bright highlights will look a little dull,
while the black shadows will look a little gray.
That's because they don't quite reach
the ends of the scale anymore.
There's nothing wrong with this,
it's just a difference
in the way the two screens show levels,
and you must account for it.
Videos set for YUV,
with its darkest and lightest pixels set to 16 and 235,
will tend to look a little flat on a computer monitor,
but perfect on a television monitor.
And that's because on a TV screen, a regular television,
0% is 16 on the RGB scale, and 100% is 235.
So these two scales don't match up perfectly.