this invention relates to a method for increasing the range of values representing a color image which exhibit a linear response . to increase the linear range , look - up tables are formed which straighten the toe and shoulder regions of film &# 39 ; s three density vs log exposure curves up to a prescribed limit . the values of the minimum densities for the piece of film containing the image are determined . the representative values of the image are then aligned with the input values of the look - up tables by a relative shift of the image values and the table values so that the minimum density values of the image equal the minimum density values in the look - up tables . the color density image is then processed through the look - up tables to increase its linear range .