Base-ratio images for representative snapshots during the event. Each EUVI 171 Å image is divided by the corresponding pre-event image taken at 18:39:45 UT. The resulting ratios are scaled into the range 0.2–1.8 for each frame. The pixel size is not rescaled, so that the solar radius differs slightly, because it is smaller by  ≈5% for STB. The temporal evolution is shown in the movies in the online edition (movie3.mpg, movie4.mpg).