avg intensity within R I_{a}(R) = \frac{∫_{0}^{R} I(r)2πrdr}{πR^{2}}

at the Petrosian radius R_{P} I(R_{P}) = η (\frac{∫_{0}^{R_{P}} I(r)2πrdr}{πR_{P}^{2}} )

F_{P} = ∫_{0}^{kR_{P}} I(r)2πrdr

C = \frac{r_{90}}{r_{50}}