Aug 04, 2021 19:00:00

Why is it difficult to make 'skin' look real with computer graphics?

In recent years,

computer graphics (CG) has made great strides, and has become established as a general method used in the production of video and image content such as animation and manga, and the production of interactive content such as games and VR. increase. Regarding 'human skin', which is especially difficult to give a realistic feeling even with such modern CG, American news media Vox explains ' why it is difficult to give a real feeling to the skin with CG'.

Why it's so hard to make CGI skin look real --YouTube


The following is a list of scenes where the main characters awaken in 'Final Fantasy Movie ' released in 2001 and 'Alita: Battle Angel ' released in 2019. There is a gap of about 20 years between the two films, and the footage shows that there was a big breakthrough in CG.

The movie version of FINAL FANTASY is one of the oldest movies in which CG-drawn realistic humans appear.

Even though they are 'real humans,' for us in 2021, the characters in the movie FINAL FANTASY have no life, frankly, like the characters in the game, because of their movements and textures. Vox points out that it looks like.

Arita: Battle Angel characters, on the other hand, have eyes and mechanical bodies that are far from real, but are closer to real humans in terms of skin.

Nick Epstein ofNew Zealand's VFX specialist Weta Digital answers the question, 'How did you get the skin to look more realistic?' Epstein was the supervisor of the visual effects division of Arita: Battle Angel and the lead technical director of Avatar.

Arita: Battle Angel is

Yukito Kijo SF comic work 'of Mr. Battle Angel Alita in SF action movie to the (Ganmu)' original, it has succeeded in depict a character close to reality by CG.

The reality is the difference between heaven and earth from the 2001 'The

Mummy Returns 2 / Golden Pyramid ' which was said to be 'too terrible'.

Compared to The Mummy 2, Arita: Battle Angel is a CG that is much closer to the performer.

'We needed to make sure that we could capture the acting of Rosa Salazar , who played the main character Alita. We thought that Rosa Salazar's acting was at the heart of the film.'

'That's why we decided to create a full-body digital version of Rosa Salazar and apply realist elements and barometers later.'

According to Epstein, there are four types of realist elements that he applied later: '

Albedo, ' ' Displacement, ' ' Subsurface, ' and 'Dynamic Changes.'

Albedo refers to the

color map that is the basis for drawing a character. If we omit all the elements such as light and consider only the color, the human face has a slightly red cheek and a slightly white forehead.

Epstein and his colleagues created a skin color map from the actual Rosa Salazar, and made adjustments to modify the color tone based on Alita's mood and physical condition. For example, in the scene where Arita is angry, the cheeks and forehead are redder and the appearance of blood on the head is reproduced.

Displacement is a technique that gives the skin a realistic feel such as greasiness by adding pore-level drawings. If you zoom in on Arita's skin, you'll see countless wrinkles.

'I'm not happy to see me in the camera, but my forehead is shining strongly, my nose is shining a little, but my cheeks aren't shining very much.'

'Each part of the face has a'line of the same glow'. Along these lines, the effect is actually applied.'

Next, 'Subsurface' will be explained by Henrik Wang Jansen, chief scientist of Luxion, who creates

3D rendering software 'KeyShot'. Janssen is a Subsurface expert and was part of a team that won the Academy Scientific and Technical Award in 2004.

Mr. Jansen specialized in the angle of reflection when light passes through the surface of an object. Janssen proved that every CG looks real when this reflection angle is simulated quickly, which has greatly contributed to the breakthrough of the entire video industry.

For example, when irradiated with laser light, the spoon reflects all the light, but human skin transmits part of the light. Mr. Jansen conducted basic research to apply this concept to CG.

For example, the full CG animation movie '

Shrek ' seems to reflect all the light it hits, so it looks unrealistic.

'In Shrek, there is a

scene where you sprinkle milk on Gingerbread man . Since Shrek does not consider the reflection of light, the milk in this scene looks like white paint.'

For this reason, Jensen wrote a treatise on simulating subsurface scattering in milk. This treatise was passed on to Shrek's creators, and the sequel '

Shrek 2 ' greatly improved the same kind of scene where gingerbread man was milked. Thanks to this achievement, Mr. Jensen was told by several strangers when he visited Sony, 'Oh, that milk!'

Subsurface scattering occurs on the skin as well as milk, but very early algorithms were designed to produce the same surface scattering on and inside the skin. Therefore, Mr. Jensen applied the idea that human skin has three layers: 'fat', 'epidermis', and 'dermis'.

In addition, we created an algorithm that causes different surface scattering depending on the color depth of the skin.

'This study has made it more compelling to render human skin.'

Epstein again talks about the final Dynamic Changes. Dynamic Changes is about facial movements, with Epstein and colleagues scanning Rosa Salazar's face reading aloud a voice-balanced collection of texts called

'Harvard Sentence,' with subtle facial expressions during conversation. The change pattern was recorded.

In the 2001 movie version of FINAL FANTASY, attention was focused on the character's 'eye movement', but in 2019 Alita: Battle Angel, the texture of the skin and the expression of light became a hot topic. 'The only question left is how real it will be,' Vox concludes the movie about this technological advance.