The parameter *brief* (with its actual uncertainty *sbrief*)
is the mean effective surface brightness, i.e. the mean surface
brightness inside the effective aperture (the circular aperture
enclosing one-half the total flux). This mean surface brightness
is expressed in *B*-.

Two equivalent measurements of brief were derived: i) from the apparent diameter enclosing a mean surface brightness of 20.75 (Dressler et al. 1987), ii) from the mean surface brightness inside the effective isophote (elliptical isophote enclosing one-half the total flux) measured by Lauberts & Valentijn (1989; LV).

where , is the standard deviation,
is the correlation coefficient and *n* the number of galaxies
used for the comparison.

Similarly we have:

where *m*'(LV) is the *average blue central surface brightness
within half total Blight* (noted in LV) , from Lauberts &
Valentijn (1989). The correction for inclination is in good agreement
with the predicted one
(see RC3 p50, Rel.71). The final value

Another estimate of the mean surface brightness is *bri*25, the mean surface
brightness inside the isophote .

This brightness must be corrected for inclination
effect (Bottinelli et al. 1995). We then obtain the corrected mean
brightness *bri*25:

where

Notations are those used for the calculation of *ai* (Sect. 7).

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