An image forming system comprising: a controller, provided with a list creation means for creating a display list by analyzing PDL data, a decompression means for decompressing compressed image data, a first drawing means for executing drawing processing based on the image data, and a print data creation means for creating the print data based on the image data, for sending to a printer; and a rasterization accelerator, provided with a second drawing means for executing drawing processing, and a first compression means for compressing the image data drawn by the second drawing means, for sending the image data to the controller; the image forming system being characterized in that: the rasterization accelerator comprises a determination means adapted to determine based on information of the display list created by the list creation means, whether to execute or not the compression of the image data by the first compression means, and a compression method in case of executing the compression by the first compression means; wherein compression processing of the image data by the first compression means includes lossless compression processing, lossy compression processing, and binarization processing; wherein the information of the display list comprises information of whether to execute or not the drawing processing by the first drawing means after executing the drawing processing by the second drawing means; and wherein with respect to image data for which the drawing processing is not to be executed by the first drawing means the determination means is further arranged to determine to use the lossy compression processing in the image data compression by the first compression means. a controller, provided with a list creation means for creating a display list by analyzing PDL data, a decompression means for decompressing compressed image data, a first drawing means for executing drawing processing based on the image data, and a print data creation means for creating the print data based on the image data, for sending to a printer; and a rasterization accelerator, provided with a second drawing means for executing drawing processing, and a first compression means for compressing the image data drawn by the second drawing means, for sending the image data to the controller; the image forming system being characterized in that: the rasterization accelerator comprises a determination means adapted to determine based on information of the display list created by the list creation means, whether to execute or not the compression of the image data by the first compression means, and a compression method in case of executing the compression by the first compression means; wherein compression processing of the image data by the first compression means includes lossless compression processing, lossy compression processing, and binarization processing; wherein the information of the display list comprises information of whether to execute or not the drawing processing by the first drawing means after executing the drawing processing by the second drawing means; and wherein with respect to image data for which the drawing processing is not to be executed by the first drawing means the determination means is further arranged to determine to use the lossy compression processing in the image data compression by the first compression means. the rasterization accelerator comprises a determination means adapted to determine based on information of the display list created by the list creation means, whether to execute or not the compression of the image data by the first compression means, and a compression method in case of executing the compression by the first compression means; wherein compression processing of the image data by the first compression means includes lossless compression processing, lossy compression processing, and binarization processing; wherein the information of the display list comprises information of whether to execute or not the drawing processing by the first drawing means after executing the drawing processing by the second drawing means; and wherein with respect to image data for which the drawing processing is not to be executed by the first drawing means the determination means is further arranged to determine to use the lossy compression processing in the image data compression by the first compression means.