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We develop a procedure for quantitative measurements on the intrinsic properties of faint galaxies allowing for the effect of the complex Hubble Space Telescope (HST) point spread function (PSF). In this, we generate simple model images, convolve them with the PSF and compare the results with the observed image of the individual object. Model parameters are then estimated from the observed images by maximizing the likelihood function, which is the probability of observing each image for any set of model parameters. Using realistic simulations of HST Wide Field Camera (WFC) images we show that we can measure unbiased sizes and magnitudes down to which we can identify and catalog a magnitude limited sample. Using simulations of WFC images we show that we can identify pure-disk from pure-bulge like galaxies in images which are more than one-magnitude brighter. To fit more realistic disk+bulge models, parameters which are not well constrained by these faint images are fixed by the mean trend seen for the brighter galaxies. Statistical results from fits to HST Medium-Deep Survey faint galaxy images are presented.
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