It seems that the defauld DPI of 'PS' device is 1000, however a plots with xsize 7 inches and ysize 3 inches is only 18.Mb under bits = 8 So it should not be a bitmap, but also should not be vector graphics as it is too large than as expected. My question is How can I control the memory cost of a EPS file generated by 'PS'? Such a eps plots generated by MATLAB is only 30 kb.