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2.7. High Quality Imaging

Typically the prime limiting factor in making an accurate analysis of a CMD is image crowding, due to overlapping stellar images. There is basically no way to ``correct'' for crowding in a CMD, so all that can be done is to estimate the size of the uncertainties that result from crowding, from incompleteness analysis (e.g. Tolstoy 1998), and apply these to any results from the interpretation of the CMD. Using HST significantly reduces crowding problems, and in certain cases, such as dwarf irregular galaxies, excellent seeing from the ground will also be sufficient to overcome severe crowding problems.