EYE ANATOMY CGI
Creation of the visual system in digital characters is a complex task. The main concern is the presence of multiple intricate details that need to work with each other and represent a certain solution for the realism. This is the reason for having access to the high quality reference of the real world. Understanding the nomenclature of the components that make up the eye and the proportion and optical specifics of each is the core principle in the approach to artificial visual apparatus.
The skin region around the eye was analysed as a compilation of lower and upper eyelid areas, the lateral and medial angle and was supported with the brow region. The structure of the eyelid is primarily an orbicularis oculi muscle that is the thinnest layer of the skin on the human body. It contains a fat layer that increases the mobility of the skin around the eyeball. It is key to draw in 2D a profile of the eye from different perspective angles to learn and embody the person- specific identity of the human eye. This is defined by the signature line profile of the window between the eyelids that are resting of the surface of the eyeball. It is important to pay specific attention to the roots of the eyelids on their end sides with the structure of ligament attachment that hold the most tension of the frontal support of the eyeball.
The lacrimal caruncle and lacrimal punctum allocated near the medial angle of the eye are both essential visual features of the human eye. The lacrimal caruncle is an in grown part of the eyeball and the optical transition between them is seamless. Apart from the optical quality of the lacrimal caruncle, specific attention has to be given to the behavioural dynamic of its shape.
This is the book I would highly recommend to get if you are doing something similar or any kinds of face CGI research and development. Or making digital humans as the practice. Including but not limited to the medical visualisation of the head and neck region of the human body.
In order to replicate a realistic human eye in three dimensional space, all parts of the human eyeball have to be built as separate pieces of geometry; the eyeball, the sclera, the iris and the lens. On average, the upper eyelid accommodates around 200 eyelashes. The strain geometry of the eyelashes has to be placed individually based on the photographic reference and have thickness relevant to reality.
Placement of the eyelashes has to intersect the eyelid surface for the post subsurface effect of the translucency in the area. From a technical perspective it is key to have access to a high resolution monitor that can obtain visual access to the fine lines of the hair and an extreme close-up of the digital eye. This will allow work on the microscopic level of details.
The iris of the human eye has the distinct property of deforming during pupil dilation. A Multi-layer approach to the human iris achieves a non-rigid deformation and optical depth. The realistic human iris painting by London-based fine artist, Marc Quinn could be a guide for creating the alpha layers for the iris disk.
The morph targets of the human face relevant to the eye behaviour such as AU43 Eyes Closed, AU45 Blink, AU41 Lid Drop and AU07 Lid Tightener, are the result of the work of separate regions of the orbicularis oculi muscle. For the same reason the area of the skin around the eye changes its form and profile with the work of the extra ocular muscles that rotate the eyeball during directional eye movements. It is key to implement the Listing Law discovered by Johann Benedict Listing (1808-1882) in the animation system. This phenomenon involves the counter rotation of the eyeball towards the origin in Z axis (the plane of the eyeball) in diagonal gaze directions. The upper and lower eyelid profile changes along with the eye movement. This is also pronounced in the lacrimal caruncle deformation and the skin area attached to the orbicularis oculi muscle. From the digital graphics perspective, it is significant to illuminate physical gaps between geometry parts to treat the region as one organ.
The refraction quality of the human cornea can be enhanced by creating artificial depth of the human iris and positioning it further inside the eyeball. The eyeball is always wet and this requires additional pieces of geometry to accommodate optical support of the eyeball and transition between the eyelids. Most of the time the eyes on digital characters appear flat due to their bright colouring. This is solved by the geometric element covering the outline of the eyelid profile to create a shadow effect. This serves to blur the transition of computer generated edges between the eyelid and the eyeball and mimic the occlusion effect.
