You just need to understand the difference between pixels per inch (ppi) and drops per inch (dpi). Each photo has a given number of pixels, and the print size will then dictate the number of pixels per inch in the final print. When you send a print job to the printer, the driver will convert to the native ppi for that printer (generally 300 ppi for Canon and 360 ppi for Epson). The the printer determines how many "dots" of each color ink to "spit" onto each pixel to give it the proper color. That's why printer specs can state, for example, up to 1500 dpi, because it can "spit" up to 5 dots of ink for each pixel at 300 ppi. If you do any sharpening of a photo and send it to the printer at a higher ppi than the printer is expecting, the driver will remove pixels and you may lose some of the sharpening effect. So, before sharpening in the the last step of post processing, you should resize the picture to the final print size (in inches) and the printer's native ppi (usually 300 or 360). After that apply sharpening and send it to the printer. Hope this is useful.