Examples of images from the HDUV (left two panels; F275W and F336W) and ancillary data (right two panels; F435W and F160W) in the GOODS-south field. The images are 0.5 arcmin on a side. Note the flat background in the WFC3/UVIS data, which was only achieved after subtraction of the sky dark. Clearly, the surface density of sources decreases to shorter wavelengths as the average galaxy exhibits a relatively red color, and sources at z ≳ 1.7 start to disappear from the UV imaging due to the Lyman break (see Figure 2). The low number density of UV-bright sources and the very high incidence of cosmic rays make it particularly challenging to align such UV imaging data (see Section 4.5).