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0:03These two scenes almost 20 years apart, both
showed their digitally created main character
0:12They also served as the big reveal of a technical
breakthrough.
0:16Final Fantasy: The Spirits Within was one
of the first movies with a realistic human
0:21CGI character — at least in theory.
0:24To our eyes today, the movement and textures
make it look at best like a video game cutscene.
0:31But focus on the skin.
0:32How did we go from lifeless skin to skin that,
on Alita, a stylized character with giant
0:38eyes and a robot body, looks so much better?
0:42How do we make fake skin look real?
0:45That journey to realistic skin includes pore
mapping, the appearance of light on apples
0:51and chicken, and knowing the difference between
a glass of whole and skim milk.
0:57I’m finding it really hard not to feel like
a total stoner thinking about my skin —
1:03I’m touching my face right now.
1:05“Honestly, when we go through looking at
this stuff, we're all doing this and like
1:09trying to look in the mirror.
1:11My name is Nick Epstein.
1:13I was a visual effects supervisor on Alita:
Battle Angel.”
1:18Alita: Battle Angel is a 2019 action movie
based on the manga and it features a stylized
1:24character that's perfectly believable.
1:26She's come a long way from this guy, the Scorpion
King from the Mummy Returns.
1:31This shot is so infamous that the VFX YouTube
channel Corridor Crew spent a whole video
1:39There are a lot of problems, but a big one
is the skin.
1:42The Mummy Returns’ Scorpion King is played
by the Rock.
1:46You wouldn't know it.
1:47But Alita definitely resembles the actor who
played her.
1:51“We needed to make sure that we were capturing
Rosa’s performance, like the heart of the
1:56movie was really Rosa’s performance as Alita.
1:58So we actually built a fully digital version
of Rosa.
2:03And then we could apply sort of our sort of
more, I guess, normal realism factors and
2:10Getting that facial model right is a crucial
first step for the skin’s movement.
2:14When the hard work begins.
2:16“I have four factors I think.
2:18Albedo, displacements, subsurface, and then
dynamic changes and deformations and so on.”
2:26Albedo is the base color map for your character.
2:30Imagine the color of a face in a void.
2:32No features, no wrinkles, no lights shining
on it.
2:36See how I make the cheeks a little red, the
forehead a little lighter.
2:41That base is crucial to realism, and it's
incredibly dynamic.
2:44Based on Rosa Salazar's real skin, they adjusted
Alita’s albedo map for different moods,
2:52“So we could then sort of compare the albedo
map when she's like really angry, for example,
2:59with a neutral pose, and then extract basically
like a blood flow map from that.
3:03And the shader could then, when she gets angry
in her performance, dial in that extra blood
3:12Displacement maps push the scan up or down.
3:14Imagine how this little guy is flat, but features
or a wrinkle here might change the height of
3:20Look at all the detail in the Scorpion King’s
face here versus Imhotep’s face in the next
3:27That's the detail you can see in the close
ups in Alita.
3:31It's way smaller than wrinkles.
3:32“We call it micro geometry, even pore level
displacement that's what gives you your oiliness,
3:38the specular response in your skin, which
you can see even just looking at me in the
3:42in the camera here, you know, my forehead
is very different to my nose, very different
3:45to my cheeks, and to my chin.
3:47Unfortunately, my forehead is quite shiny,
my nose also shiny, but my cheeks less so
3:52and that they're fairly isotropic, without
direction, I have a very clear flow direction
3:57that way, a flow direction this way.
3:59We have a sort of reverse flow direction around
my chin.
4:02So we actually draw curves on along these
flow lines.
4:07Some extreme close ups, we you know, we knew
that the camera was going to basically fly
4:12But the difference between this face and this
one isn't just the skin.
4:16It's what happens beneath it.
4:18“My name is Henrik Wann Jensen, and I'm
the chief scientist of Luxion, makers of Keyshot.
4:24And I specialize in computer graphics, in
answering the question why do things look
4:29the way they do and how can you simulate it
on a computer?
4:33See when we wrote the first paper as you may
have noticed, we did some measurements in
4:39So we actually went to the local supermarket
with a laser pointer.
4:42I was shining on on the on the milk, we were
shining on the meat.
4:45And actually the guys who ran the supermarket
came to us and what are you doing?
4:50The big idea of that breakthrough 2001 paper,
work that got the team to the technical Oscars,
4:58was that the way they'd seen light bounce
through food was true of almost everything.
5:03And if it could be simulated more quickly,
that would make all computer graphics look
5:08more real, including skin.
5:11See how the laser bounces off the spoon?
5:14But when I put my hand in front of it, the
light passes through, and even bounces around
5:20This drawing breaks down as an illustration,
because light passes through and bounces under
5:27Computers could simulate subsurface scattering,
like they do with this marble.
5:31But they did it by simulating every single
bouncing light photon.
5:36That took way too long.
5:38So most of the time, computer animation couldn't
bother with it.
5:41It makes the Rock look wrong — light is
bouncing off him, not passing through the
5:48It affected other shots, too.
5:49“In Shrek, they actually have a cookie guy
and some milk.
5:53And if you ever see that shot, it looks like
white paint, which was exactly the example
5:57we said if you don't do this properly, it's
actually going to look like white paint.”
6:01Jensen and his colleagues figured out how
to simulate subsurface scattering more efficiently.
6:06That changed animation.
6:08“Then in Shrek 2, they now knew about this
technology.
6:11And then they went all in on the milk.
6:13So they had a ton of milk.
6:14But they now did the full subsurface scattering.
6:17And so it had a little bit of an impact on
that as well.
6:22it's funny because I went to talk to Sony
and you never know what people are interested
6:28They say, oh, you're the milk guy.”
6:29Subsurface scattering could efficiently simulate
the different ways light passed through whole
6:34versus skim milk, and also skin, or at least
the beginning of it.
6:38“But when we created the initial subsurface
scattering algorithm, you're set up based
6:43on this assumption that you hit the skin and
then everything is the same underneath.
6:47And of course, real human skin is not like
that.
6:50We have different layers like epidermis, dermis.
6:53And we looked at sort of the basic things
that decide what humans can look like.
6:57And it turns out melanin, you actually have
different melanin types, we have one that's
7:00lighter melanin type, one that's more on the
brown side, on the dark side, you have to
7:05have mixtures of those to get the correct
skins.
7:07You could actually do a very convincing, now,
rendering of human skin.”
7:12“So, you know, I've talked about how we
define regions for micro geometry, some of
7:19the things we did also revolved around dynamic
scans.
7:23So we actually had footage of what scan data,
so it's this 3d three dimensional data of
7:30Rosa running through Harvard lines of sort
of every expression we could we could ask
7:37Harvard lines are a series of sentences that
help hit all the phonemes—chunks of speech
7:44It's for audio, but it can help artists see
every possible way somebody's mouth can move
7:49when they're talking.
7:51I'm doing this video.
7:53It includes these things called Harvard lines,
and I was hoping you could read some of them.
7:59[Reading overlapping Harvard lines]
8:08Early reviews for Final Fantasy: The Spirits
8:10Within focused on it as a treat for the eyeballs.
8:14Since then, increasingly complex simulations
of not just skin but light and movement have
8:20made visual effects look even more real.
8:22The only question is how much further is left
to go.
8:26“Take the winding path to reach the lake,
note closely the size of the gas tank.
8:32It snowed rained and hailed the same morning
the meal was cooked before the bell rang.
8:39What joy there is in living.”
8:45“One of the immediate effects that that
sort of the visual effects industry they jumped
8:49on right away was if you also have someone
who's lit from behind, you see light passing
8:54If you look at movies like like Harry Potter
with Dobby, the character, they were the first
8:59to really adopt this technology.
9:01They all had big ears so they were very excited
about that, and you'll see a lot of glowing
9:04light coming through the ears.”
