  This paper is concerned with the applications of local features of the
quaternion Hardy function. The feature information can be provided by the polar
form of the quaternion Hardy function, such as the local attenuation and local
phase vector. By using the generalized Cauchy-Riemann equations of local
features, four various kinds of edge detectors are newly developed. The
experiment results show that the amplitude-based edge detectors perform the
envelope of test images while the phase-based edge detectors give the detail of
the test images. Our proposed algorithms greatly outperform existing schemes.
