  We present direct measurements of the limb-darkened intensity profiles of the
late-type giant stars HR5299, HR7635, and HR8621 obtained with the Navy
Prototype Optical Interferometer (NPOI) at the Lowell Observatory. A triangle
of baselines with lengths of 18.9 m, 22.2 m, and 37.5 m was used. We utilized
squared visibility amplitudes beyond the first minimum, as well as triple
amplitudes and phases in up to 10 spectral channels covering a wavelength range
of ~650 nm to ~850 nm. We find that our data can best be described by
featureless symmetric limb-darkened disk models while uniform disk and fully
darkened disk models can be rejected. We derive high-precision angular
limb-darkened diameters for the three stars of 7.44 mas +/- 0.11 mas, 6.18 mas
+/- 0.07 mas, and 6.94 mas +/- 0.12 mas, respectively. Using the HIPPARCOS
parallaxes, we determine linear limb-darkened radii of 114 R$_\odot \pm $13
R$_\odot$, 56 R$_\odot \pm $4 R$_\odot$, and 98 R$_\odot \pm $9 R$_\odot$,
respectively. We compare our data to a grid of Kurucz stellar model
atmospheres, with them derive the effective temperatures and surface gravities
without additional information, and find agreement with independent estimates
derived from empirical calibrations and bolometric fluxes. This confirms the
consistency of model predictions and direct observations of the limb-darkening
effect.
