  We developed an automated method for sunspot detection using digital
white-light solar images to achieve a performance similar to that of visual
drawing observations in sunspot counting. To identify down to small, isolated
spots correctly, we pay special attention to the accurate derivation of the
quiet-disk component of the Sun, which is used as a reference to identify
sunspots using a threshold. This threshold is determined using an adaptive
method to process images obtained under various conditions. To eliminate the
seeing effect, our method can process multiple images taken within a short
time. We applied the developed method to digital images captured at three sites
and compared the detection results with those of visual observations. We
conclude that the proposed sunspot detection method has a similar performance
to that of visual observation. This method can be widely used by public
observatories and amateurs as well as professional observatories as an
alternative to hand-drawn visual observation for sunspot counting.
