For some datasets, such as the SDSS (York et al. 2000), the data release includes an atlas of pre-cut postage stamps. For other applications, such as in relatively shallow galaxy-galaxy or cosmic shear/flexion studies, fields will be relatively uncrowded and thus simple application of widely used packages such as SExtractor (Bertin & Arnouts, 1996) can be used.

When fields are crowded, however, and contain a wide range of brightnesses and sizes, the catalog generation becomes more complicated. It has been noted by Rix et al. (2004) that in general, a single set of SExtractor parameters is insufficient for detection of all the objects of interest within an image; setting the source detection threshold too low will result in excessive blending near bright objects, whereas a high threshold results in a failure to detect fainter sources. Rix et al. describe a two-pass strategy for object detection and deblending involving an initial (“cold”) pass to identify large, bright objects, followed by a lower-threshold (“hot”) pass to pick up dimmer objects. Their final catalog consists of all the objects detected in the cold run, plus any objects detected in the hot run that do not lie within the isophotal area of any object 