Home

Introduction: What is an RTI?

Reflectance Transformation Imaging, also called polynomial texture mapping, is a method of mapping the surface of an object by changing light sources. This is a useful method because it is an affordable way to get extremely accurate representations of features that aren't visible under common lighting and magnification.

RTI's can be created in a number of ways. The most basic of these is manually moving a light source around an object at carefully measured locations while taking a picture of the resulting shadows cast on the object's surface. Unfortunately, these images need to be taken in the dark, so these measurements are challenging. Our chosen design is an automated version of this solution which mimics this by placing a dome over the object with the many light sources included as stationary LEDs on the dome. The benefits include more accurate positioning of light sources, a dark area within the dome without needing a dark room, and photography of surfaces that require more dangerous wavelengths, such as UV.

While the dome is not a new idea, our implementation of it has a GUI which makes it highly adaptable without a need to change configurations or the program, along with many features rarely seen in RTI systems, such as 64x three-color light sources (UV, near-IR, and visible white). Beyond this, we focused on keeping costs low, so any amount of LEDs can be safely left unused, and the program will account for the missing LEDs after a simple GUI configuration.

Our Open Source RTI

Many solutions exist for Reflectance Transformation Imagers, but very few designs are affordable and capable of multicolor imaging, which is important for materials transparent in the visible spectrum. This project on Hackaday, for a single-color dome, was the basis for our design.

This repository contains our RTI's hardware and software implementation and includes the source and documentation for:

1. A custom-designed Arduino Mega shield to control the dome, which powers a three-color LED matrix and triggers the cameras.
2. Another custom circuit board that holds all three colors of LEDs in a smaller area than if we had three separate boards, allowing for a more compact dome.
3. The program to control the dome, with a serial or GUI control interface.
4. The GUI within the above program, which enables easy control over the whole system with no need for technical knowledge. See more about the GUI on our system overview page.

Take a look at About the System for a more detailed look at what's included and for links to further documentation.