A (large) subset of the full data set will be used in this exercise. The original data set contained 16, 16, 24 and 16 exposures, in y, b, v and u, respectively. Each exposure contained four separate images, PC, WF2, WF3 and WF4. Each image contained 800x800 pixels. In this exercise, we will intend to process the PC and the WF3 images, in filters y, b and v. Subimages of size 512x512 will be used. We will use 12 images for each filter. The full data set is available locally. Each group will process a different data set, and the result must be combined from all groups, in order to derive CMD and metallicity information.