Visualisation of image-scale matching: using the positions of the three subcomponents (red, blue, green dots) in each image, the multiple images A, B, C, and D are mapped onto each other (red arrows, indicating that the dots of each colour are mapped onto each other). This mapping determines the local lens properties on the image scale (indicated by the larger red areas for visualisation purposes, as the convex hull spanned by the reference points in each image is too small to be drawn). Visualisation of subcomponent-scale matching (highlighted in blue): using the Gaussians fitted to a subcomponent (here: for the first subcomponent denoted by 1, highlighted in dark grey), the subcomponents can be matched onto each other (as indicated by mapping the dots of each colour onto each other at the subcomponent scale) to determine the local lens properties within the area of the Gaussians. The first reference point in each Gaussian is its centre of light (yellow dots). The two reference points that are further required are the end points of the axes of the elliptical isocontour (brown, white dots).