  The Sunrise Chromospheric Infrared spectroPolarimeter (SCIP) has been
developed for the third flight of the SUNRISE balloon-borne stratospheric solar
observatory. The aim of SCIP is to reveal the evolution of three-dimensional
magnetic fields in the solar photosphere and chromosphere using
spectropolarimetric measurements with a polarimetric precision of 0.03\%
(1$\sigma$). Multiple lines in the 770 and 850 nm wavelength bands are
simultaneously observed with two 2k$\times$2k CMOS cameras at a frame rate of
31.25 Hz. Stokes profiles are calculated onboard by accumulating the images
modulated by a polarization modulation unit, and then compression processes are
applied to the two-dimensional maps of the Stokes profiles. This onboard data
processing effectively reduces the data rate. SCIP electronics can handle large
data formats at high speed. Before the implementation into the flight SCIP
electronics, a performance verification of the onboard data processing was
performed with synthetic SCIP data that were produced with a numerical
simulation modeling the solar atmospheres. Finally, we verified that the
high-speed onboard data processing was realized on ground with the flight
hardware by using images illuminated by natural sunlight or an LED.
