The Unknown Face

November 11th, 2018

Last year, to commemorate the 100 years since the end of WWI, FFParis, commissionned Merci-Michel, where I was working at the time, to create a portrait in memory of the people who fought during the war.
The portrait is exposed at the Historial of the Great War of Péronne.


I initially made some prototypes with a limited set of images found on the Internet. In the two first iterations I simply aligned the portraits based on the position of the eyes.

In the first one I tried to make an evolving portrait by picking colors on a subset of the images and drawing tiny circles on the final image. The images in the subset were regularly replaced to produce an evolving portrait.
The second is simply a superposition of the images
The last one uses face detection to align the portraits. This is the approach we eventually used.

Generating the portrait

Each image is processed using BRFv4. This provides triangles for each image.
I normalized the triangles and made a map where each triangle is associated to a unique color. This way I could easily associate each pixel of the final image to a pixel in the sources images and perform a fast mapping.

In a first time I processed the images in batches to make sure I could resume the process if it was interrupted.
This iterative approach produced undesirable artifacts so I abandonned it, but it allowed me to collect intermediate results that make a nice sequence:

This is the image generated using 30,000 portraits.
15 additional portraits were added on top of this image to produce a more natural face.


By far the most collossal task in this project was the collection of all the original photos. This hard work was done by a team from F&F who scanned thousands of pages from dozens of books.
On our side we worked on a tool to help them extract the portraits from the scans. It allowed them to ensure a consistent size for all the images as well as make sure the faces were correctly detected.


A website shows a selection of the images that compose the portrait.


The project was mentionned by the french President on Twitter.
It is the subject of an exercise in a school book.