  A photometric study of 22 disk galaxies at redshifs z=0.5-2.6 is conducted,
using deep NICMOS J and H band and STIS open mode observations of the HDF-S
NICMOS parallel field. Rest-frame B-profiles and (U-V) color profiles are
constructed. A number of disks show steeper decrease of luminosity than
exponential, referring to disk truncation. Shape of the luminosity profiles
does not vary with redshift, but galactic sizes decrease significantly. (U-V)
colors and color gradients suggest more intense and centrally concentrated star
formation at earlier epochs. On the basis of (U-V) color and chemical evolution
models, the disks at z~2.5 have formed between z=3.5-7. The studied parameters
are idependent of absolute B luminosity within the sample.
