Raster image processor is decisive in modern digital printing machines. Three random number generators were examined for their applicabilities to raster image processor. Results show that random number generator should be carefully selected in terms of the screen cell size adopted: linear congruential generator (LCG) is the best for the screen cell size of 8 × 8 or 16 × 16; multiplicative congruential generator (MCG) is most desirable when the screen cell size equals to 6 × 6 or 12 × 12; in the case of 24 × 24 screen cell size, either LCG or MCG is optimum. The workflow of raster image processor was optimized according to our results. These findings are helpful to improve the performance of digital press that is equipped with raster image processor.