The Archival Pure Parallel Project processed and combined with state-of-the-art tools about 2,000 WFPC2 images, primarily in the wide UBVI filters, obtained in parallel with other HST instruments. The
Holwerda et al. examined 32 HST/WFPC2 archival fields of 29 spiral galaxies (Sab and later) for their paper The Opacity of Spiral Galaxy Disks. IV. Radial Extinction Profiles...