A newly developed isochrone synthesis algorithm for the photometric evolution of galaxies is described .
Two initial mass functions , IMFs , in particular , the recent IMF determined by Kroupa , Tout , and Gilmore , three photometric transformations , and a 1-Gyr-burst star formation rate , SFR , are used to compute the B - V and V - K color index evolution .
Non-negligible differences are observed among model results .

In the framework of the galaxy count model by Colín , Schramm , and Peimbert a simple merging scenario is considered to account for the excess of galaxies observed in the blue band counts .
The excess is explained by the number and luminosity evolution of a group of galaxies called interacting , I .
It is assumed that the number of I galaxies increases as ( 1 + z ) ^ { \eta } due to mergers .
Moreover , it is proposed that their characteristic luminosity increases as ( 1 + z ) ^ { 3 } due to starbursts driven by galaxy-galaxy collision and decreases as ( 1 + z ) ^ { - \eta } due to the change in the size of the galaxies .
Not much number evolution is needed to account for the excess ; for example , a model with \eta = 4.0 predicts that about 17 % of the galaxies at z = 0.4 are interacting .
Number evolution models with a rather high value of \eta fit better the data ; in particular , the model with \eta = 4.0 predicts that about 13 % of the galaxies have z > 0.7 in the 21.0 < m _ { b _ { J } } < 22.5 interval , this contrasts with the upper bound of 5 % obtained with the sample of 78 galaxies by Colless et al .
The excess of high redshift galaxies can not be simply explained by changing reasonably the parameters of the luminosity function of I galaxies .
This result could indicate that mergers are not the whole story .
Our best-fit model produces the following values for the parameters of the local luminosity function of galaxies : \alpha = -1.20 , M ^ { * } = -20.7 , and \phi ^ { * } = 1.66 \times 10 ^ { -3 } Mpc ^ { -3 } ( h = 0.5 ) .