Use TOTAL pixels, not dpi. Otherwise you may get into a situation where your image is a nice 600 dpi --- but only two inches across. Almost all paint and graphic conversion programs can adjust the display or preferred dpi of an image, and instruct a printer as to how to interpret the pixels into the desired image space. So, in short...look at the size you need and multiply by the dpi you need then render at the resulting numbers, x pixels by y pixels.