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In this work,we determine the parameters of spiral structure for a sample of face-on spiral galax-ies.In practice,the solution to this problem is a hard task because of the diversity of observed characteris-tics associated with spiral structure,such as the number of arms,their shape,arm contrast,etc.We study spiral structure in galaxies based on an analysis of photometric cuts perpendicular to the arm direction.The method is based on an approximation of these slices with an analytical function and derivation of the parameters of spiral structure(arm width,asymmetry,pitch angle)using the fitted parameters from this approximation.The algorithm has been applied to a sample of 155 galaxies selected from the Sloan Digital Sky Survey in different passbands.In this paper,we only consider the results on arm width:most spirals exhibit an increase in their width with galactocentric distance.Only 14 per cent of galaxies in our sample show an opposite trend or have an almost constant arm width at all radii.