Context. The chromospheric Hα spectral line is a strong line in the spectrum of the Sun and
other stars. In the stellar regime, this spectral line is already used as a powerful tracer of …

The strong chromospheric absorption lines Ca ii H & K are tightly connected to stellar
surface magnetic fields. Only for the Sun, spectral activity indices can be related to evolving …

Abstract Information regarding edges is essential for many fields of image processing. A
classical edge detection method, such as the Canny algorithm, uses the gradient of an …