# Internal extinction: ai

The dust extinction within galaxies in the B-band, `ai [mag]` is
computed after Bottinelli
et al. 1995, A&A296, 64.

This formula is a function of the morphological type, `t`,
and of the apparent flattening, `logr25`.

where m_{0} is the corrected magnitude and m_{i} is the
observed one;

`R` is the axis ratio derived from logr25

`k` is the bulge to disk ratio and depends on morphological type as follows: `k=0.754*10`^{(-0.2*t)},
`if k >1 then k=1` (Simien and de Vaucouleurs)

`K` is the coefficient `dlogD/db` (where `D` is the isophotal diameter at surface brightness `b`).
It depends on the morphological type `t` as:

`K = 0.12-0.007*t if t < 0.`

`K = 0.094 if t >= 0.`

and `C` is defined as `(dlogD/dlogR)` and has the fixed value of 0.04