You are now offered to choose a segmentation algorithm ("segmenter") amongst the currently implemented ones.
The choice is actually quite limited. Apart from the '''Manual segmentation''', you will find 3 segmenters, but they are all based on [http://en.wikipedia.org/wiki/Blob_detection#The_Laplacian_of_Gaussian LoG segmentation]. They are described in detail elsewhere, but here is what you need to know.
* The '''Log segmenter''' applies a plain LoG segmentation on the image. All calculations are made in the Fourier space, which makes it optimal for intermediate spot sizes, between ≈5 and ≈20 pixels in diameter.
In our case, let us just use the '''Dog segmenter'''.