  We present an astrometry and photometry catalogue of globular cluster (GC)
candidates detected with HST WFPC2 in a sample of 19 early-type galaxies,
appropriate for comparison to the low-mass X-ray binary (LMXB) populations
observed with Chandra. In a companion paper, we present the Chandra data and
investigate the relation between these populations. We demonstrate that,
although there is little evidence of a colour-magnitude correlation for the
GCs, after estimating mass and metallicity from the photometry, under the
assumption of a single age simple stellar population, there is a significant
positive correlation between mass and metallicity. We constrained [Z/H] =
(-2.1+/-0.2)+(0.25+/-0.04)log M, with a 1-sigma intrinsic scatter of 0.62 dex
in metallicity. If GCs are bimodal in metallicity this relation is consistent
with recent suggestions of a mass-metallicity relation only for metal-poor
clusters. Adopting a new technique to fit the GC luminosity function (GCLF)
accounting for incompleteness and the Eddington bias, we compute the V-band
local GC specific frequency (Sn) and specific luminosity (Sl) of each galaxy.
We show that Sl is the more robust measure of the richness of a GC population
where a significant fraction is undetected due to source detection
incompleteness. We find that the absolute magnitude of the GCLF turnover
exhibits intrinsic scatter from galaxy to galaxy of ~0.3mag (1-sigma), limiting
its accuracy as a standard distance measure.
