Lambertian Portraits

Photographs by Greg Halvorsen Schreck
Concept and Software by Mark Woodworth

Lambertian Portraits are digital photographs, made out of wood.

Unlike conventional photographs, they aren’t defined by pigment, ink, or emulsion, nor are they projected, or virtual images. Rather, they are formed by light raking across the surface contours. The tones are simply shadows.

The science of the images is based on Lambert’s Law, from 1760. Lambert’s equation calculates the diffuse reflection intensity of a surface based upon the angle of illumination and the angle of observation.

Programmers use this principle to render objects realistically in 3-D computer programs.

Mark Woodworth, an industrial physicist, coded Lambert’s equation into a software program that translates grayscale pixel densities into angular surface changes that can be milled onto a wood surface.

Each photograph combines around 96 separately machined pieces of wood viewed from the side. In normal room light, an image can barely be perceived.

The object looks like a peculiar sculptural construction. Illuminated properly with a single light source, the wood magically transforms into a black-and-white photograph.

The poetry of each portrait comes from its concave quality. The photograph is hollowed out of the wood, a subtractive process. The sitter leaves a space behind, an absence.

These pieces exist in conversation with the words of author and art critic John Berger: “What is a likeness? When a person dies, they leave behind, for those who knew them, an emptiness, a space: the space has contours and is different for each person mourned. This space with its contours is the person’s likeness and is what the artist searches for when making a living portrait. A likeness is something left behind invisibly.”A demonstration of the illumination process, with explanation by Mark Woodworth, can be found here.




Greg Halvorsen Schreck has gone through many incarnations and reincarnations as a photographer in the past 35 years. As he explores the epistemological shift from analog to digital photography, he sometimes experiments with hybrid optical possibilities. His 1 projects are connected to portraiture, human rights issues, landscapes, and environmental concerns. His most recent exhibition in 2018, reflected his time in Guatemala with the Quiche Maya. It consisted of portraits and a visual interpretation of the Popol Vuh, the Mayan creation story.

Schreck teaches analog and digital photography and other art classes at Wheaton College, near Chicago. His undergraduate degree is from Rochester Institute of Technology, where he studied both commercial and fine art photography. Schreck completed his graduate work at New York University and the International Center of Photography. He lives in Wheaton, Illinois with his family.

You can see examples of his work at


A teenage infatuation with photography led Mark Woodworth to study physics, including experimental quantum optics, at the University of Chicago. The laser in his photon echo experiment fired ten times a second, faster than he could write down numbers, so he learned computer data acquisition. He eventually dropped out of the 23rd grade to try a job writing software for a year. Thirty years later he’s still in that same job, automating warehouses. As part of his work, he developed a system that uses lasers, cameras, and computers to measure the size of boxes moving at high speeds on conveyors. He has enjoyed collaborating with Greg on projects at the intersection of photography, physics, and computing. No lasers so far, however. He lives in Oak Park with his patient and understanding wife, Randi Ravitts Woodworth. They have two lovely daughters, Madeleine and Katherine.