  Direct imaging of circumstellar disks requires high-contrast and
high-resolution techniques. The angular differential imaging (ADI) technique is
one of them, initially developed for point-like sources but now increasingly
applied to extended objects. This new field of application raises many
questions because the disk images reduced with ADI depend strongly on the
amplitude of field rotation and the ADI data reduction strategy. Both of them
directly affect the disk observable properties. Our aim is to characterize the
applicability and biases of some ADI data reduction strategies for different
disk morphologies. A particular emphasis is placed on parameters mostly used
for disks: their surface brightness, their width for a ring, and local features
such as gaps or asymmetries. We first present a general method for predicting
and quantifying those biases. In a second step we illustrate them for some
widely used ADI algorithms applied to typical debris disk morphologies:
inclined rings with various inner/outer slopes and width. Last, our aim is also
to propose improvements of classical ADI to limit the biases on extended
objects. Simulated disks seen under various observing conditions were used to
reduce ADI data and quantify the resulting biases. These conclusions
complements previous results from NaCo L' real-disk images of HR4796A. ADI
induces flux losses on disks. This makes this technique appropriate only for
low- to medium-inclination disks. A theoretical criterion is derived to predict
the amount of flux loss for a given disk morphology, and quantitative estimates
of the biases are given in some specific configurations. These biases alter the
disk observable properties, such as the slopes of their surface brightness or
their radial/azimuthal extent. Additionally, this work demonstrates that ADI
can very easily create artificial features without involving astrophysical
processes.
