Table 7.

Summary of some secondary histogram parameters

Parameter	Derivation	Relationship to image features
Mean of positive pixels (MPP)	Considers only pixels greater than 0	Reduces the impact of dark objects on the mean histogram value
Proportion of positive pixels (PPP)	The fraction of pixels in the filtered image with values greater than 0	Reflects the number of objects (positive or negative) highlighted by the filter
Variance	SD2	Approximately linear relationship with the number of objects highlighted but approximates an exponential relationship with their mean intensity difference compared with background
Kurtosis reciprocal	1/(kurtosis + 3)	Approximates a linear relationship with number of objects highlighted. Reduced by intensity variations amongst highlighted objects
Normalized SD	ln(SD)/ln(pixel number)	Relates SD to the potential variability for the region size