Blur 
Bias 

Click 3 points on dish edge to define each circle mask.
Drag to adjust.
Double click to copy the first circle somwhere else.
Press 'Enter' to count.
Press 'Delete' to undo.


Blur determines the radius(px) of the noise reduction.
This should be some fraction of the size of a colony.

Bias separates smudges from cells.
If cells are being ignored, decrease the value.
If smudge is being counted, increase the value.