In the world of AI image generation, the difference between a generic "AI face" and a compelling, lifelike character often lies in the details of bone structure and emotional expression. By specifying face types and distinct facial movements in your prompts, you can move beyond the defaults of tools like Stable Diffusion, Midjourney, or DALL-E to create unique, balanced individuals.
Part 1: Understanding Geometric Face Types
A character's face shape is determined by the proportions of the forehead, cheekbones, jawline, and chin. Defining these helps the AI establish a consistent "look" for your character.
1. The Oval Face
Description: Balanced and symmetrical; longer than it is wide with gently rounded contours. The forehead is slightly wider than the chin.
Aesthetic: Often viewed as the "ideal" proportion in classical art.
Prompt Keyword: “Oval face shape, symmetrical features, high cheekbones.”
2. The Round Face
Description: Equal width and length with full cheeks and a soft, curved jawline.
Aesthetic: Conveys youthfulness, friendliness, or softness.
Prompt Keyword: “Round face, soft jawline, full youthful cheeks.”
3. The Square Face
Description: A strong, angular jawline that is roughly the same width as the forehead.
Aesthetic: Conveys strength, authority, and presence.
Prompt Keyword: “Square face, strong angular jaw, broad forehead.”
4. The Diamond Face
Description: Narrow forehead and chin, with the cheekbones being the widest point of the face.
Aesthetic: Angular, elegant, and striking.
Prompt Keyword: “Diamond face, prominent high cheekbones, pointed chin.”
5. The Heart Face
Description: A wide forehead that tapers down to a narrow, often pointed chin.
Aesthetic: Romantic and delicate.
Prompt Keyword: “Heart-shaped face, wide forehead, delicate pointed chin.”
6. The Pear (Triangle) Face
Description: A narrow forehead that widens into a broad, defined jawline and chin.
Aesthetic: Earthy, strong, and grounded.
Prompt Keyword: “Pear-shaped face, broad jaw, narrow temples.”
7. The Oblong (Rectangle) Face
Description: Elongated proportions with straight sides; the forehead, cheekbones, and jaw are of similar width.
Aesthetic: Sophisticated and mature.
Prompt Keyword: “Oblong face, elongated proportions, straight jawline.”
Part 2: Capturing Emotive Expressions
Once the structure is set, adding expression brings the character to life. These descriptions focus on the muscle tension and eye/mouth positions that convey deep emotion and intensity.
ExpressionVisual IndicatorsUse CaseEcstasyEyes rolled back/half-closed, mouth open in a gasp, flushed skin.Peak intensity, euphoria.StrainedFurrowed brows, clenched teeth, squinted eyes.High effort, physical tension, combat, or climax.Moaning/GaspingO-shaped mouth, parted lips, quivering chin.Vocal release, building pleasure or shock.Joyful/SmilingUpward curved mouth, "Duchenne" crinkled eyes.Connection, happiness, lightheartedness.Biting LipLower lip caught in teeth, half-smirk, lowered gaze.Seduction, concentration, or playfulness.ImmersedEyes tightly shut, relaxed brows, internal focus.Deep meditation, sensory focus, or intimacy.FlushedReddening of the cheeks and neck, dilated pupils.Arousal, embarrassment, or physical exertion.
Pro-Tips for Prompt Engineering
To get the most out of these face types and expressions, follow these best practices:
Combine Structure and Emotion: Don't just prompt a face type. Combine them: "A man with a square face and a strained grimace, furrowed brows, cinematic lighting."
Use Descriptive Modifiers: Words like "hyperrealistic," "sharp focus," and "subsurface scattering" help the AI render the skin textures (like blushing or sweat) that make expressions look real.
Specify the Camera Angle: Expressions look different from different perspectives. A close-up or macro shot will emphasize the subtle quivering of a lip or the dilation of a pupil.