Name: Why it’s so hard to make CGI skin look real
Uploaded: 2022-08-25T06:51:18.000Z
Duration: 9 min 7 s
Description: Thousands of YouTube videos with English-Chinese subtitles! Now you can learn to understand native speakers, expand your vocabulary, and improve your pronunciation...

Adverbs of manner

These two scenes almost 20 years apart, both showed their digitally created main character

They also served as the big reveal of a technical breakthrough.

Final Fantasy: The Spirits Within was one of the first movies with a realistic human

To our eyes today, the movement and textures make it look at best like a video game cutscene.

How did we go from lifeless skin to skin that, on Alita, a stylized character with giant

eyes and a robot body, looks so much better?

That journey to realistic skin includes pore mapping, the appearance of light on apples

and chicken, and knowing the difference between a glass of whole and skim milk.

I'm finding it really hard not to feel like a total stoner thinking about my skin —

“Honestly, when we go through looking at this stuff, we're all doing this and like

I was a visual effects supervisor on Alita: Battle Angel.”

Alita: Battle Angel is a 2019 action movie based on the manga and it features a stylized

She's come a long way from this guy, the Scorpion King from the Mummy Returns.

This shot is so infamous that the VFX YouTube channel Corridor Crew spent a whole video

There are a lot of problems, but a big one is the skin.

The Mummy Returns' Scorpion King is played by the Rock.

But Alita definitely resembles the actor who played her.

“We needed to make sure that we were capturing Rosa's performance, like the heart of the

movie was really Rosa's performance as Alita.

So we actually built a fully digital version of Rosa.

And then we could apply sort of our sort of more, I guess, normal realism factors and

Getting that facial model right is a crucial first step for the skin's movement.

Albedo, displacements, subsurface, and then dynamic changes and deformations and so on.”

Albedo is the base color map for your character.

No features, no wrinkles, no lights shining on it.

See how I make the cheeks a little red, the forehead a little lighter.

That base is crucial to realism, and it's incredibly dynamic.

Based on Rosa Salazar's real skin, they adjusted Alita's albedo map for different moods,

“So we could then sort of compare the albedo map when she's like really angry, for example,

with a neutral pose, and then extract basically like a blood flow map from that.

And the shader could then, when she gets angry in her performance, dial in that extra blood

Displacement maps push the scan up or down.

Imagine how this little guy is flat, but features or a wrinkle here might change the height of

Look at all the detail in the Scorpion King's face here versus Imhotep's face in the next

That's the detail you can see in the close ups in Alita.

“We call it micro geometry, even pore level displacement that's what gives you your oiliness,

the specular response in your skin, which you can see even just looking at me in the

in the camera here, you know, my forehead is very different to my nose, very different

Unfortunately, my forehead is quite shiny, my nose also shiny, but my cheeks less so

and that they're fairly isotropic, without direction, I have a very clear flow direction

We have a sort of reverse flow direction around my chin.

So we actually draw curves on along these flow lines.

Some extreme close ups, we you know, we knew that the camera was going to basically fly

But the difference between this face and this one isn't just the skin.

“My name is Henrik Wann Jensen, and I'm the chief scientist of Luxion, makers of Keyshot.

And I specialize in computer graphics, in answering the question why do things look

the way they do and how can you simulate it on a computer?

See when we wrote the first paper as you may have noticed, we did some measurements in

So we actually went to the local supermarket with a laser pointer.

I was shining on on the on the milk, we were shining on the meat.

And actually the guys who ran the supermarket came to us and what are you doing?

The big idea of that breakthrough 2001 paper, work that got the team to the technical Oscars,

was that the way they'd seen light bounce through food was true of almost everything.

And if it could be simulated more quickly, that would make all computer graphics look

But when I put my hand in front of it, the light passes through, and even bounces around

This drawing breaks down as an illustration, because light passes through and bounces under

Computers could simulate subsurface scattering, like they do with this marble.

But they did it by simulating every single bouncing light photon.

So most of the time, computer animation couldn't bother with it.

It makes the Rock look wrong — light is bouncing off him, not passing through the

“In Shrek, they actually have a cookie guy and some milk.

And if you ever see that shot, it looks like white paint, which was exactly the example

we said if you don't do this properly, it's actually going to look like white paint.”

Jensen and his colleagues figured out how to simulate subsurface scattering more efficiently.

“Then in Shrek 2, they now knew about this technology.