[Instructor] As mentioned earlier, our eyes are not
very good at accurately perceiving color.
In fact, they're so poor at seeing color relative to our
perception of luminance, that image technology manufacturers
have learned they can discard much of the color
information in an image, interpolate the remaining
color information, and we won't notice.
By the way, interpolate is just a long word
for averaging out.
Choosing not to record color information for particular
pixels in an image is called color spacing
or color sub sampling, and there are a few approaches to it.
The principal is very simple and the results
can be impressive.
You can store less information making the file smaller
so you don't need as much storage space or bandwidth
to transmit the image, and the audience perceives
good quality, color rendition.
Color spacing is indicated using three numbers.
The first number is kind of the beats in the bar for music.
It tells you how the image has been divided up
for the purposes of color spacing.
A common option is four, so let's start with that.
The second number represents the pixels on the odd
horizontal rows, or lines of pixels.
The third number represents the pixels on the even rows.
So, if you have four, four, four, color spacing,
every pixel will have luminance information and all
the pixels on the odd lines will have color information
and all the pixels on the even lines will, too.
This means there's no color spacing, really,
every pixel has full information,
and this is the maximum quality possible
when considering color spacing as an option.
If you're working on chromo key, that is, choosing to make
pixels transparent based on their color,
and I'll be covering this later, you're converting
color into an alpha-channel adjustment.
If some of your pixels don't have color information,
it can produce worse results.
So, it's worth working with four, four, four
media if you can, but let's look at a common alternative
and that's four, two, two.
In this example, only every other pixel on the odd lines
and every other pixel on the even lines
has any color information.
Literally no color information is recorded
for the other pixels.
It's amazing, the colors for these pixels that don't
have color information are worked out
by averaging their neighbors.
So, how 'about four, two, zero?
Well, once again, every pixel has luma values, every other
pixel on the odd lines have color information,
and none of the pixels on the even lines
have any color information at all.
In this example, only one pixel in four
has any color information.
How 'about three, one, one?
In this example the beats in the bar are set to three
so now, as always, every pixel has luminance information,
but only every third pixel of both the even and odd lines
has any color information.
So, 2/3 of the color information is missing.
Is this better, is it worse, is it desirable?
As with every system of this kind, it's always going
to be a trade off between quality and convenience.
If we could work with full quality images all of the time,
we probably would, but the file systems and the performance
of our editing systems when doing so
just don't make it worthwhile.
We always find a balance between acceptable quality
and our high standards as creative professionals.