What are the key elements of a smile that can be analyzed through photography

Okay, so I’m working on a project that involves analyzing smiles in photographs, both to understand genuine emotion versus performative smiles, and also to potentially train a computer vision algorithm to recognize different types of smiles. I’m not a psychologist or facial recognition expert, so I need some guidance.

Specifically, I’m looking for a breakdown of the visual elements of a smile that can be objectively assessed in a photograph. Think of it like what a scientist would look for.

Beyond the obvious ("are the lips upturned?"), I’m interested in:

• Detailed muscle engagement: What specific muscles around the eyes, cheeks, and mouth are typically involved in different kinds of smiles? How can you tell in a photo whether those muscles are truly engaged or just superficially moved? (e.g., can you really see the Duchenne marker in a 2D image?)
• Wrinkle patterns: Where do wrinkles typically form with a genuine smile, and how do they differ from wrinkles formed by forced or fake smiles?
• Teeth exposure: What’s the ideal amount of teeth to be visible for different types of smiles (e.g., a relaxed smile vs. an excited smile)? Is there a correlation between the amount of gum shown and the genuineness of the smile?
• Lip shape and symmetry: How does the shape of the lips change during a smile? Is a perfectly symmetrical smile always a genuine smile, or can asymmetry indicate something about the emotion behind it?
• Changes around the eyes: How can you distinguish between squinting due to light versus the crow’s feet associated with a genuine smile? What other changes occur around the eyes when someone is truly happy and smiling?

I’m particularly interested in pointers to academic research or established facial action coding systems (like FACS) that can help me quantify these elements. I’m hoping to find a systematic way to analyze these features from photographs. Can you help me break down what I should be looking for?

Answer

The analysis of a smile in photography involves examining numerous subtle elements that contribute to its overall appearance and perceived authenticity. These elements can be broadly categorized as follows:

1. Lip Morphology and Movement:

• Lip Curvature: The upward curve of the lips is a fundamental characteristic of a smile. The degree of curvature, whether slight or pronounced, influences the perceived intensity and sincerity of the smile.
• Lip Symmetry: Ideally, both sides of the lips should rise symmetrically. Asymmetry can indicate forced smiles, discomfort, or underlying neurological issues. The degree of asymmetry can be measured and assessed.
• Lip Thickness: The inherent thickness of the lips plays a role in how prominent the smile appears. Thicker lips can create a more visually striking smile.
• Lip Exposure: The amount of upper and lower lip exposed during the smile is significant. A genuine smile often exposes more of the upper lip. The ratio of upper to lower lip exposure can also be considered.
• Philtrum: The philtrum, the vertical groove between the base of the nose and the upper lip, can flatten or deepen during a smile. This change can be a subtle indicator of muscle engagement.
• Vermilion Border: The definition and prominence of the vermilion border (the edge of the lip) can enhance the smile’s attractiveness.
• Teeth Visibility: The extent to which teeth are displayed when smiling.

2. Dental Display:

• Number of Teeth Shown: The number of upper teeth visible during the smile is a key aesthetic factor. A broader smile typically reveals more teeth.
• Gingival Display ("Gummy Smile"): The amount of gum tissue visible above the upper teeth is another consideration. Excessive gingival display can be perceived as less aesthetically pleasing, although preferences vary. The amount of gingival exposure is measured in millimeters.
• Tooth Shape and Alignment: The shape, size, and alignment of the teeth contribute to the overall aesthetics of the smile. Crooked or uneven teeth can detract from the smile’s perceived attractiveness.
• Tooth Color: The shade and brightness of the teeth affect the smile’s radiance. Discoloration or staining can diminish the smile’s impact.
• Dental Arch: The curvature of the dental arch (the alignment of the upper teeth) influences the shape and fullness of the smile.
• Incisal Edge Display: The visibility and contour of the incisal edges (the biting edges) of the upper front teeth are important aspects of smile design.

3. Muscle Activation and Facial Wrinkling:

• Zygomaticus Major Muscle: This muscle is primarily responsible for pulling the corners of the mouth upward. Its activation is crucial for a genuine smile.
• Orbicularis Oculi Muscle: This muscle surrounds the eyes and contributes to the formation of "crow’s feet" wrinkles when genuinely activated (Duchenne smile).
• Nasolabial Folds: The depth and prominence of the nasolabial folds (the lines running from the nose to the corners of the mouth) can increase during a smile, particularly a wide one.
• Cheek Elevation: The degree to which the cheeks are raised is correlated with the intensity of the smile.
• Forehead Movement: In some individuals, the forehead muscles may activate slightly during a genuine smile, leading to subtle wrinkling.

4. Eye Region:

• Crow’s Feet: The presence and intensity of crow’s feet wrinkles are strong indicators of a genuine, Duchenne smile.
• Eye Squint: The degree to which the eyes narrow or squint during the smile can reflect its intensity and authenticity.
• Lower Eyelid Elevation: The raising of the lower eyelid can contribute to the overall appearance of a genuine smile.
• Eyebrow Movement: Subtle eyebrow movements can accompany a smile and influence its perceived emotional tone.

5. Facial Context and Overall Expression:

• Head Tilt: The angle of the head can influence how the smile is perceived.
• Facial Symmetry (Overall): General facial symmetry contributes to attractiveness and perceived health.
• Skin Tone and Texture: The overall condition of the skin can affect the aesthetic appeal of the smile.
• Emotional Context: The surrounding facial expression and the overall emotional context can provide further insights into the sincerity and meaning of the smile.

By carefully analyzing these elements in a photograph, one can gain a deeper understanding of the smile’s characteristics, its authenticity, and its impact on the overall facial expression. Software and trained specialists can be used to automate and augment parts of this analysis.