convenience all density values of the image have been normalized between 0 and 1 0 being white and 1 being black on the same scale of density values the print densities of the digital processor are d 0 0 d 1 0 30 d 2 0 50 d 3 0 80 and d 4 1 0 at start an instruction 30 is issued to generate a 4 by 4 assigned density value array fig4 a from the scanned input data according to a prescribed tone reproduction curve logic function generator such as illustrated in fig1 this instruction represents the input to output density transformation including any desired tone enhancement adjustments the result of the instruction is a 4 by 4 array of assigned density values which are stored in the memory of processor 20 fig5 and serves as the starting point the remaining sequence is indicated by the directional arrows then an instruction 32 is issued to compare the assigned density arrray fig4 a with a print density table figure 4b stored in memory and generate the computed density array fig4 c each entry of the array is a computed individually if an entry of the assigned density array happens to be exactly one of the print density values then this density value will be taken as the computed density value this is the case of the assigned density value located at the row 1 and column 1 1 1 location of the array fig4 a.