Since the Zernike moments are defined over the unit circle, two steps
were required to convert a rectangular region of each image to a unit
circle for calculation of Zernike moments. First, the `center of
fluorescence' (analogous to the center of mass) for each image was
calculated and used to define the center of the pixel coordinate
system. Second, the x and y coordinates were divided by 150 (this
corresponds to the size of an average cell at the magnification used
in these experiments). Only pixels within the unit circle of the
resulting normalized image, f(x,y), were used for subsequent
calculations. The Zernike moments, Z_{nl}, for an image were then
calculated using
Zernike moments through degree 12 were calculated (Z_{nl} such that in Equation 2.4) using the code in Section 5.2.1 (p. ). Since the moments themselves are complex numbers and are sensitive to rotation of the image, the magnitudes of the moments were used as features (i.e. |Z_{nl}|) [21]. This provided 49 descriptive features for each image.