An initial step: Similar to a singl

An initial step: Similar to a single-resolution edge detection method, the first step of this method starts
with Sobel edge detection and followed by the Canny edge detection. However, this time a large
value of smoothing parameter of the Canny edge detection is used (i.e.
√
10). A large value
of smoothing parameter is used because in an initial step we only need to roughly estimate the
boundary of the algae in an image. The true boundary will be detected in the next refinement step.