  High-sensitivity imaging of ultracold atoms is often challenging when
interference patterns are imprinted on the imaging light. Such image noises
result in low signal-to-noise ratio and limit the capability to extract subtle
physical quantities. Here we demonstrate an advanced fringe removal algorithm
for absorption imaging of ultracold atoms, which efficiently suppresses
unwanted fringe patterns using a small number of sample images without taking
additional reference images. The protocol is based on an image decomposition
and projection method with an extended image basis. We apply this scheme to raw
absorption images of degenerate Fermi gases for the measurement of atomic
density fluctuations and temperatures. The quantitative analysis shows that
image noises can be efficiently removed with only tens of reference images,
which manifests the efficiency of our protocol. Our algorithm would be of
particular interest for the quantum emulation experiments in which several
physical parameters need to be scanned within a limited time duration.
