RelightLab is an open-source application for the creation or relightable images (RTI: Reflectance Transformation Imaging), using a collection of images sharing a common viewpoint and different light direction. It supports legacy formats such as .ptm and .rti, as well as a newer format suitable for efficient web visualization (through the lib OpenLime). It replaces the RTIBuilder outdated and unsupported Java application, and add new features, such as normal computation, lights 3d geometry, etc.