Measures

Dynaface computes the measurements below from landmarks it places automatically: 98 points on a frontal face, in the WFLW layout, and six points along the outline of a profile. The Python and .NET libraries and the desktop and mobile apps all use the same definitions. Landmark numbers on this page refer to the landmark figure.

Each measure is a plugin class. all_measures() returns all of them, and analyze() returns their outputs by name, such as results["fai"]. The apps use the same names for their CSV columns.

How values are reported

• A standard image. Each photo, and each frame of a video, is scaled and cropped to a standard 1024 by 1024 image, with the pupils 260 pixels apart, before anything is measured.
• Millimeters. Distances (mm) and areas (mm²) are converted from pixels by assuming the pupils are 63 mm apart, the adult average. Set the subject's own pupillary distance when absolute sizes matter. Ratios and angles don't depend on it.
• Left and right are the subject's own sides. In an ordinary, unmirrored photo, the subject's right side is on the left of the image. A mirrored selfie swaps them.
• Symmetry ratios divide the smaller side by the larger, so 1.0 means the two sides are equal and lower values mean more asymmetry.
• Missing values. A value that can't be determined, such as an angle whose profile point wasn't found, is NaN. If a measure can't run at all, its outputs are None.

Summary

Measure	View	Outputs	Description
FAI	frontal	fai	Facial Asymmetry Index (FAI): how much the distance from each eye's inner corner to the same side's mouth corner differs between the two sides, in millimeters.
Oral CE	frontal	oce.l, oce.r	Oral commissure excursion (Oral CE): the distance from each corner of the mouth to the middle of the lower lip, in millimeters.
Brow	frontal	brow.d	Brow height: the difference in height between the middles of the two brows, in millimeters, measured along lines parallel to the line between the pupils.
Dental Display	frontal	dental_area, dental_left, dental_right, dental_ratio, dental_diff	Dental display: the area of the mouth opening inside the lips, in square millimeters, split at the facial midline.
Eye Area	frontal	eye.left, eye.right, eye.diff, eye.ratio	Eye area: the area of each eye opening (palpebral fissure), in square millimeters.
Intercanthal Distance	frontal	id	Intercanthal distance: the distance between the inner corners of the eyes, in millimeters.
Mouth Length	frontal	ml	Mouth length: the distance between the corners of the mouth, where the lips meet, in millimeters.
Nose Frontal	frontal	nose.alar, nose.nostril	Nose widths seen from the front, in millimeters, between landmarks on the nose's lower outline.
Outer Eye Corners	frontal	oe	Outer eye corners: the distance between the outer corners of the eyes (lateral canthi), in millimeters.
Lateral Measures	lateral	nfa, nla, at, nt, at_nt	Measures of a side profile, from the landmarks found along its outline.
Position	frontal, lateral	tilt, px2mm, pd	Position: the head's tilt in the image, the distance between the pupils, and the millimeters-per-pixel scale that converts every measurement.
Pose	frontal, lateral	pitch, roll, yaw	Pose: the head's rotation, in degrees, as estimated by the landmark model.
Skin Tone	frontal	hue, sat, brightness	Skin tone: the average color of both cheeks, as hue, saturation and brightness.
Landmarks	frontal	landmark-1-x to landmark-98-y (196 values)	Landmarks: the position of each of the 98 landmarks, in pixels, for export.

Frontal symmetry

Facial Asymmetry Index (FAI)

The distance from the inner corner of each eye (medial canthus) to the corner of the mouth (oral commissure) on the same side, compared between the two sides. FAI is the absolute difference between the left and right distances, in millimeters, so 0 means the two sides match. For the index's validation in smile restoration research, see Malm et al., 2018.

The two distances FAI compares.

Calculation: the right distance is from landmark 64 to 76 and the left from 68 to 82; fai is the absolute difference between them. FAI tells you how unequal the sides are, not which side is longer.

Output	Description	Units
fai	Difference between the left and right canthus-to-commissure distances	mm

API: AnalyzeFAI

Oral Commissure Excursion (Oral CE)

The distance from each corner of the mouth to the midpoint of the lower lip, in millimeters, reported separately for the left and right sides. Comparing values at rest and during a smile shows how far each corner moves.

Each corner of the mouth to the middle of the lower lip.

Calculation: oce.r is the distance from landmark 76 to 85, and oce.l from 82 to 85.

Output	Description	Units
oce.l	Left corner of the mouth to the middle of the lower lip	mm
oce.r	Right corner of the mouth to the middle of the lower lip	mm

API: AnalyzeOralCommissureExcursion

Brow height (Brow)

The difference in height between the left and right eyebrows, in millimeters, measured at the middle of each brow.

Lines through the middle of each brow, parallel to the line between the pupils.

Calculation: a line is drawn through the middle of each brow's upper edge (landmarks 35 and 44), parallel to the line between the pupils, and brow.d is the vertical distance between the two lines. When the pupils are level, that's the difference in height between the two landmarks. Like FAI, it doesn't say which brow is higher.

Output	Description	Units
brow.d	Difference in height between the brows	mm

API: AnalyzeBrows

Eye area

The area of each eye opening (palpebral fissure), outlined by eight landmarks around the eyelid margins, in mm². Dynaface reports each side, the difference between them and their symmetry ratio.

The two eye openings, filled.

Calculation: the right eye is the polygon through landmarks 60 to 67, and the left eye through 68 to 75.

Output	Description	Units
eye.left	Area of the left eye opening	mm²
eye.right	Area of the right eye opening	mm²
eye.diff	Difference between the two areas, rounded to 0.01	mm²
eye.ratio	Symmetry ratio of the two areas	none

API: AnalyzeEyeArea

Dental display

The area of the mouth opening inside the inner edges of the lips, where the teeth show during a smile, in mm². The opening is split at the facial midline, and Dynaface reports the total, each side, the difference between the sides and their symmetry ratio.

The subject's right half of the opening in red, the left in blue.

Calculation: the opening is the polygon through the inner-lip landmarks 88 to 95. The midline is perpendicular to the line between the pupils, through its middle; the subject's right half is the part on the image's left. With the mouth closed, every area is 0 and the ratio is 1.

Output	Description	Units
dental_area	Total area of the opening	mm²
dental_left	Area of the left half	mm²
dental_right	Area of the right half	mm²
dental_ratio	Symmetry ratio of the two halves	none
dental_diff	Difference between the two halves	mm²

API: AnalyzeDentalArea

Frontal distances

Intercanthal distance

The distance between the inner corners of the eyes, in millimeters: landmarks 64 and 68.

Output	Description	Units
id	Distance between the inner corners of the eyes	mm

API: AnalyzeIntercanthalDistance

Outer eye corners

The distance between the outer corners of the eyes (lateral canthi), in millimeters: landmarks 60 and 72.

Output	Description	Units
oe	Distance between the outer corners of the eyes	mm

API: AnalyzeOuterEyeCorners

Mouth length

The distance between the corners of the mouth, measured where the lips meet, in millimeters: the inner-lip landmarks 88 and 92.

Output	Description	Units
ml	Distance between the corners of the mouth	mm

API: AnalyzeMouthLength

Nose (frontal)

Two widths of the nose seen from the front, in millimeters, measured between points on the nose's lower outline: the alar width, between the outer edges of the nostrils (landmarks 55 and 59), and the nostril width, between the middles of the two nostrils (56 and 58).

Output	Description	Units
nose.alar	Alar width	mm
nose.nostril	Nostril width	mm

API: AnalyzeNoseFrontal

Head position, pose and color

Position

The head's tilt in the image (the angle of the line between the pupils), the distance between the pupils in pixels, and the resulting millimeters-per-pixel scale used for every millimeter measurement.

The facial midline, perpendicular to the line between the pupils.

Calculation: tilt is 0 when the pupils are level, and positive when the pupil on the image's right is lower. Dynaface doesn't straighten tilted faces unless you give load_face_image() a tilt_threshold, and then tilt is what remains after straightening. px2mm is the subject's pupillary distance (63 mm unless you set it) divided by pd. For a profile, where both pupils can't be seen, px2mm is fixed at 0.24.

Output	Description	Units
tilt	Angle of the line between the pupils	degrees
pd	Distance between the pupils in the standard image	pixels
px2mm	Millimeters per pixel	mm

API: AnalyzePosition

Pose

Estimated head rotation in degrees: pitch (nodding up and down), yaw (turning left and right) and roll (tilting toward a shoulder). Useful for checking that a subject was facing the camera.

Calculation: the landmark model, SPIGA, estimates the head pose along with the landmarks. Dynaface also uses the yaw to decide whether a photo shows a profile. Pose only writes its values on the image.

Output	Description	Units
pitch	Nodding up or down	degrees
roll	Tilting toward a shoulder	degrees
yaw	Turning left or right	degrees

API: AnalyzePose

Skin tone

The average color of two patches on the cheeks, as hue (degrees), saturation and brightness (percent). Lighting, white balance and makeup all change it, so compare photos taken under the same conditions. The apps don't chart it for video.

The average color, as a swatch in the corner.

Calculation: Dynaface averages the color of two rectangles, one on each cheek between the outline of the face and the side of the nose (bounded by landmarks 2, 3 and 55 on the right, and 30 and 59 on the left), in the image before anything is drawn on it. The average is converted to hue, saturation and value (brightness), and each is rounded down to a whole number.

Output	Description	Units
hue	Hue, from 0 to 360	degrees
sat	Saturation	percent
brightness	Brightness (value)	percent

API: AnalyzeSkinTone

Landmarks

The position of every landmark, so you can calculate your own measures. It also draws the landmarks as dots.

The outputs are numbered from 1, for spreadsheets: landmark-1-x is the x of landmark 0 in the landmark figure, and landmark-98-y the y of landmark 97. Coordinates are in pixels of the standard image, with the origin at the top left.

Output	Description	Units
landmark-1-x to landmark-98-y	The x and y of each of the 98 landmarks	pixels

API: AnalyzeLandmarks

Profile (lateral)

When a photo shows the face from the side, Dynaface removes the background, traces the outline of the face from forehead to chin, and marks six points along it: soft tissue glabella, soft tissue nasion, nasal tip, subnasal point, mentolabial point and soft tissue pogonion. These measurements are taken relative to the image's horizontal and vertical axes, so keep the head level in profile photos. They all come from one measure class.

The angles and tip projection, and on the right, the traced outline with the six points found on it.

Nasofrontal angle (NFA). The angle at the soft tissue nasion between the soft tissue glabella and the nasal tip, in degrees. It describes how deep the nasion is: larger angles mean a smoother, flatter nasal root, and smaller angles a deeper nasion. It's typically between 115° and 135°.

Nasolabial angle (NLA). The angle at the subnasal point between the nasal tip and the soft tissue pogonion, in degrees. It describes the angle of the base of the nose relative to the lower face. The classic nasolabial angle uses lines along the columella and the upper lip instead, so the two aren't directly comparable.

Nasal tip projection (AT/NT). AT is the horizontal distance from the nasal tip back to a vertical line through the soft tissue nasion, and NT is the vertical distance from the nasion down to the level of the tip. Their ratio, AT/NT, describes how far the tip projects relative to the length of the nose: higher ratios mean a more prominent tip. AT and NT are in pixels of the standard image, and the ratio has no units.

Output	Description	Units
nfa	Nasofrontal angle	degrees
nla	Nasolabial angle	degrees
at	Horizontal distance from the nasal tip to the nasion's vertical	pixels
nt	Vertical distance from the nasion to the level of the tip	pixels
at_nt	Ratio AT/NT	none

The measure's tip_proj item switches the drawing of AT and NT on and off; it has no value of its own. For a frontal photo, this measure returns no outputs.

API: AnalyzeLateral