8-bit vs. 10-bit – you might have heard these terms before, but what exactly do they
mean?
When should you use one over the other?
For Starters, 8-bit isn’t this!
8-bit video is everywhere.
Regardless of how it was originally shot.
DVDs, Blu-rays, TV and almost anything you see online is generally in 8-bit.
So, if 8-bits are enough for a Hollywood blockbuster, that you watch from the comfort of your own
home, then why would you ever, need to shoot in 10-bit?
Well what we’re really talking about is something known as bit depth or color depth.
Bit depth can be thought of as how many possible gradations of color there are in an image.
It is not the same as color gamut, which is the range of possible color.
You can have 256 shades of red, blue, or green in an 8-bit image, but with 10-bit video,
you can have 1024 shades!
Do we really need that many shades?
Well that depends on who you ask.
10-bit video has existed for many years in the professional broadcast and film world,
but only now are we really seeing it come into the mainstream.
You can thank three different trends for making this possible: Cameras with log modes, easily
accessible color grading software, and more recently, delivering in HDR with wider color gamuts
Ask anyone who’s tried to grade a log image, and they’ll tell you that you can only do
so much with 8-bit video.
With only 256 shades per color, some scenes can exhibit what’s called “banding”
in what should be a smooth gradient.
In other instances, banding doesn’t appear until you color grade, meaning you can only
push the image to a certain degree.
You don’t have a lot of wiggle room in 8-bit, meaning you have to get your exposure correct
in camera.
Now while you can use a log mode with an 8-bit camera it’s not always a great idea, and
some log modes handle it better than others.
Canon’s original C-Log for example, was designed for 8-bit video.
It does hold up pretty well.
You see, standard Rec. 709 footage can present roughly 5-6 stops of dynamic range, so when
you’re using a non-log, or normal mode those 8-bits only have to be spread across a picture
that doesn’t utilize the sensor’s entire range.
Log modes exist in order to get every stop out of the sensor into a limited space, so
when you record this way, you’re using those same 8-bits across far more information, which
then needs to be stretched out later.
You can actually visualize this if you look at a waveform monitor.
As you add curves or adjust levels, you’re stretching the data of the video out, revealing
“gaps” in the image.
Banding is exactly what happens when these gaps become too prominent.
But, shooting in 10-bit solves this.
Now, all that information from the sensor can be defined in 1024 steps, allowing for
more drastic color grades, and smooth gradients in places like skies.
Let’s say that Rec. 709 has “regular old blue”, while P3 or Rec. 2020 have “brilliant blue”.
I just made those up.
8-bit color can still display “brilliant blue”, but it’s going to have fewer shades
between that and “regular old blue.”
The larger your gamut, the more challenging it is for an 8-bit mode to accurately represent it.
This is why HDR requires a minimum of 10-bits.
GRRRRRRRRR.
But, that still does not answer how nearly every form of video gets away with it.
I know this is going to sound weird, but believe it or not, for most types of video, 8-bit
works just fine.
Provided you have the bitrate, all it takes, is a little bit of noise.
Don’t believe me?
Watch what happens when I add just a small bit of noise to this image.
The banding is a lot less noticeable.
And just like we could see the gaps in the waveform, you can see the noise filling-in those gaps.
When professional content is finished in 10-bits or more, the version you end up seeing comes
from that source.
It’s a lot like how a 4k image looks really sharp and clean when downscaled to 1080p.
The process in this case is called “dithering” and it blends colors together using noise.
On top of this, most movies, even those shot digitally, have a form of sensor noise or
film grain that hides the limits of 8-bit recording.
Lastly, just because you shoot 10-bit, doesn’t mean you need a 10-bit monitor to appreciate the gains.
Yes, it’s true.
The most accurate representation and benefits of 10-bit can only be seen on a 10-bit display.
However, shooting and especially grading in higher bit depths still gives you added flexibility
that you see in the final image.
Those cleaner gradients for example, are still visible in the 8-bit monitor that you or anyone
else has.
In fact, it’s the monitor or graphics card you have that is dithering the image before
you even see it.
So if you aren’t doing heavy grading, or better yet, if you’re not using a log mode
at all, shooting in 8-bits isn’t all that bad.
That said, if you shoot in log modes, and want to perform extensive, creative color
grades, you will definitely want to shoot in 10-bit.
And if you want to produce HDR content, you’re actually required to shoot in at least 10-bits!
As always consider the needs of your production.
From B&H, this is Doug, I’ll see you next time.