  The Hubble Space Telescope has obtained some of its well-deserved impact by
producing stunning three-color (RGB) pictures from three-band imaging data.
Here we produce a new RGB representation of the $I$, $V$, and $B$ bandpass
images of the HST Ultra Deep Field (HUDF). Our representation is based on
principles set forth elsewhere (Lupton et al 2004, PASP, 116, 133--137). The
principal difference between our RGB representation of the data and the more
traditional representation provided by the Space Telescope Science Institute is
that the (necessarily) nonlinear transformation between data values and RGB
values is done in a color-preserving (i.e., hue- and saturation-preserving)
way. For example, if one of the image pixel values saturates the dynamic range
of the RGB representation, all three of the R, G, and B values in the
representation are truncated such that the hue and saturation of the pixel is
the same as it would have been if the pixel had had lower flux but the same
astronomical color. This, in effect, makes the bright parts of the
representation an informative color map, not "whited out" as they are in
traditional representations. For the HUDF, this difference is seen best in the
centers of bright galaxies, which show significant detail not visible in the
more traditional representation.
