Fig. 3. An illustration of the methodology employed to estimate the diffusion coefficient values of bulk sperm (D value). The processed image showing diffused bulk sperm is divided into small rectangular zones (gray rectangles) of 29.5–31.5 µm width. The average light intensity of each rectangular zone (I value) and the location of its center along the length of the channel (x value) are recorded. The I values are normalized (called I_n values and shown in the figure) using the intensity value of the corresponding sample (I_o value). The x values as X coordinates and I_n values as Y coordinates are supplied to the MATLAB curvefitting toolbox. The D value is obtained by curve-fitting Eqn 6 to the I_n–x data. Not all I_n and x values are shown for the sake of clarity. erf, error function.