Sintel's Eyes

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Sintel's Eyes

Postby meestaplu » Fri May 28, 2010 7:13 am

I checked the Blender site today (it's been a while...) and saw the Project Durian updates. I am amazed to see how well the Durian team is using Blender's new features -- subsurface scattering and all that jazz, nice!

The animation looks like it's coming along nicely, and I really like Sintel's stylized realism.

Her eyes, though, bother me.

Project Durian header image:

High res reference, from Google Image Search:

Problem image:

In the header image of, her eyes look reasonably ok. When looking directly forward, the incorrectly stylized anime eye doesn't fall into the uncanny valley, but there are latent problems in the model and the rig. I will explain later what I mean by "incorrectly stylized".

To understand the problem, it is helpful to examine a reference image of a human eye. In the reference image given above, several anatomical features are prominent.

Around the eye:
- The upper and lower lashes, the upper denser than the lower.
- The lacrimal caruncle, the small pink recess nearest the nose
- The almond-shaped space created by the folds of the upper and lower lids.
- The interface between the lid and the eye is pink but not inflamed.

The eye itself:
- The pupil, whose diameter ranges between about 10% and 50% of the distance between eyelids at normal opening (without a squint or a wide-eyed gaze).
- The iris, whose diameter is about 100-110% of the distance between eyelids at normal opening.
- The intense and varied coloration of the iris.
- The milky white (not completely white) sclera.

Sintel's eye is not all bad. Several features are very well presented. The difference in density between the upper and lower lashes is evident. In the header image, it looks like she is wearing eyeliner on the upper lid. The pupil dilates in low light and the sclera's milky white color has been captured effectively.

Several features, though, are problematic, especially so because of her high level of realism. Her thin, satisfied smile, her nose, and the hair falling on her face bring me closer to her. However, when I look at her eye lines to determine if her smile is real or fake, and when I try to follow her gaze, I trip up. As a cartoon character her eye issues would be fatal, and her stylized realism combines with the problems to propel her deep into the uncanny valley. The most important part of capturing a real human character is properly rendering the eyes.

Her eyes are incorrectly stylized. They look like a 3D version of the typical western misinterpretation of the anime style. Cartoon anime eyes are almost rectangular, and this does not translate well to the 3D world, where eyeballs are typically modeled, as they are here, as textured spheres.

The problems:

The caruncle is much reduced in the stylized eye as compared to the reference. The purpose is probably to capture what we notice as beautiful instead of putting this pink blob in the corner of the eye. In a realistic eye and surrounding skin, though, the caruncle is important. Using a correctly proportioned caruncle reduces the size of the sphere that represents the eyeball.

Because the eyeball sphere is too large, the eyeball extends too far towards the nose. As a result, the eyelids must conform to a spherical surface for too long a distance. Sintel's eyelids turn down where the caruncle should be. This would not be a problem if they were following a planar surface at that point, but they are not.

In a real eye, the part of the eyelid close to the caruncle barely moves when the eye closes. In Sintel's eyes, though, the eyelid must move far in order to cover the entire eye. However, the eyelid is rigged as if a caruncle were present, leaving these weird humps in her lower eyelid. This is the biggest problem with the rig. Adding a caruncle and reducing the size of the eyeball would fix it.

The disproportionately large eyeballs cause more problems. The pupils are too close together and the irises are much too large. As a result, Sintel's eyes look really weird when she looks to one side or the other, as she is in the problem image.

I'm not a pro modeler or animator by any means, so I hope this is helpful. Best of luck on Project Durian!

I love vector calculus at 4 in the morning.

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