A computer system having a printer driver to convert received data into print data according to a user's printing order is provided that enhances printing speed by minimizing the amount of print data that is generated by compressing and converting image data. The printer driver has a determining part to determine whether the received data is image data; an image analysis part to divide the image data into one or more detail areas according to the amount of change between pixel data constituting the image data, and to select a best appropriate compression program applied for each detail area from a plurality of compression programs; a compressing part to compress each detail area by using the best appropriate compression program in the plurality of compression programs; and a converting part to convert compressed data from the compressing part into the print data.