- [Instructor] Let's start out with how bright a pixel is.
Remember, while we're talking generally about images
or even a stream of images making video,
your camera, computer, and screen
are all really thinking about individual pixels
in a particular location in the image.
So when we talk about things like bit depth,
color mode, and so on,
we're really talking about the rules
that apply to each individual pixel.
Bit depth simply means how many bits,
that's our ones and zeros,
are used to record how bright a pixel is,
or how red, how blue, or green.
And we'll get to color in the next lesson.
For now, let's start out with the brightness.
Each pixel has a number that defines how bright it is.
We should start with what we mean
by fully bright and fully dark.
And there's a big debate about this that's ongoing,
and it may never be resolved.
But for now, let's just say
there's an amount of brightness
that's as bright as the pixel can be,
and we'll call that fully on.
Or as they would say in regular color theory,
we'll call that one.
And then there's an amount of brightness that's fully off,
and we'll call that zero.
These amounts of brightness don't represent
the maximum or minimum brightness possible in the universe.
You can just consider the surface of the sun, for example,
relative to the brightness of the image in your TV.
There's a big difference between the two.
Or the darkest.
Instead, they represent the brightest
and darkest states for a pixel.
And this applies equally
to the brightest and darkest states
for a photo receptor on a camera, too.
If we were using just one bit
to record the brightness of a pixel,
it would have just two states.
And that would be fully dark or fully light.
If we had two bits used,
we'd have four possible combinations.
So I suppose that would be off,
a little bit on, quite a lot on, and fully on.
If we add another bit, we have eight possible combinations.
And as you might guess,
having eight bits means we have 256 possible combinations.
And this is exactly how eight bit color works.
We have one minor issue, though.
We can't use these numbers from one to 256
because we need a zero.
For this reason, eight bit color
is on a scale from zero to 255.
You've probably seen these two numbers lots of times
at the ends of adjustment controls,
and now you know why.
Every extra bit doubles the number of steps.
We've pretty much skipped through nine bit color,
so now we often have 10 bit,
which would go from one to 1,024.
So that's double 256 is 512, and double again is 1,024.
But again, because we need a zero,
this actually goes from zero to 1,023.
This factor, the number of bits used
to record the color or light information,
is called the bit depth.
Bigger is better, but it also means bigger files
and more work for computers to record,
play back, and make adjustments to those pixels.
There's just that much more information being used.
The benefit of having more steps
between no light at all and fully light is clear.
The more steps, the more subtle
the journey from dark to light.
So you avoid posterizing or having visible steps
when you have subtle gradients.
There comes a point, of course,
where human vision is incapable
of discerning any more subtle adjustment
from one step to the next,
and this is a hotly-debated number.
You'll also hear about 16 bit and 32 bit processing.
This means working out effects with very, very subtle steps,
so that the processing effectively loses no picture quality.
In any case, however many bits are used
to measure the amount of light,
the measurement will be a number.
Bigger numbers produce brighter pixels,
and the more numbers you use to define the grayscale,
the more subtle it will be.