Facial thirds
Face height divided into hairline→glabella, glabella→subnasale, subnasale→menton, each as a percentage of the total.
Depends on the user-placed hairline (trichion) — no detector locates it and it moves with hairstyle.
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Typical adult faces show a lower third slightly larger than the middle third, and an upper third that varies enormously with hairline. Reading a "short" or "long" third as a flaw is not supported by the literature — equal thirds are the exception in every population studied.
0% of a Southern Chinese sample had equal thirds; 91% of Saudi men and 88% of Saudi women had a lower third larger than the middle. In practice the lower third is usually the largest.
Conformity in published samples: east asian 0% · middle east m 5%
The upper third depends entirely on the user-placed hairline; the middle and lower thirds are the meaningful comparison.
Why every value has an error bar
Every value Canthion reports carries a 1σ uncertainty propagated from MediaPipe Face Mesh's published accuracy (3.96% of inter-ocular distance mean absolute error per landmark, Kartynnik 2019). For a typical 300 px inter-pupil photo that is ≈12 px per landmark, which is why small ratios and angles get wide intervals. A number without an interval is a number pretending to be more precise than it is.
References
- Farkas, Hreczko, Kolar & Munro (1985). Vertical and horizontal proportions of the face in young adult North American Caucasians: revision of neoclassical canons. Plast Reconstr Surg 75(3):328–338. pubmed.ncbi.nlm.nih.gov/3883374/
- Jayaratne, Deutsch, McGrath & Zwahlen (2012). Are Neoclassical Canons Valid for Southern Chinese Faces? PLoS ONE 7(12):e52593. doi.org/10.1371/journal.pone.0052593
- Al-Sebaei (2015). The validity of three neo-classical facial canons in young adults originating from the Arabian Peninsula. Head Face Med 11:4. doi.org/10.1186/s13005-015-0064-y
- Khoshab et al. (2022). Historical Tools of Anthropometric Facial Assessment: A Systematic Raw Data Analysis on the Applicability of the Neoclassical Canons and Golden Ratio. Aesthet Surg J 42(1):NP1–NP10. doi.org/10.1093/asj/sjab339
Related: how bone-level measurements are taken from a photo · methodology · all insights