As I've said, I send 360ppi to my Epson and have done so all the way back to the 1994 Epson Stylus Color printer. For smaller prints for which I have more data than 360ppi, I sometimes upsample to 720ppi.
I don't know the Mac OS, but on Windows, the Graphics Device Interface (GDI) is basically concerned with screen draws. There is obviously the printer function calls necessary to facilitate printing, but the actual data handling and conversion is done by the driver (more a full featured program in Epson's Case). The Windows GDI printer calls are
here. The only thing that comes into play is the DeviceCapabilities function call the application makes to populate the INTERNAL printing dialog boxes. One value it can request is DC_ENUMRESOLUTIONS in which it passes back the resolutions capable by the printer. However, I've never seen an application actually use this function and instead requires you to go into the into the Epson printer properties box, not part of GDI,...something like this:
As we are all aware, Epson does not present an option to change 'resolution' directly, but based on combination of settings like Media Type, Print Quality and Finest Detail checkbox affect a change in printer quality indirectly to 720x720, 1440x720, 2880x1440, etc.
Question: You are saying if I write a program that issues a DeviceCapabilities function call to the Epson printer, it will report back 360 and 720, 1440 or whatever depending on the printer model?
DWORD
DeviceCapabilities(
_In_ LPCTSTR pDevice,
_In_ LPCTSTR pPort,
_In_ WORD
DC_ENUMRESOLUTIONS,
_Out_ LPTSTR pOutput,
_In_ const DEVMODE *pDevMode
);
Jeff, unfortunately, on the the Windows platform I don't see how one could save the image to PDF without specifically giving the application a resolution setting or printing to PDF which also entails setting the output parameters. There does not seem to be a method on Windows to use printing settings for the Epson and then save as PDF instead except maybe printing to a FILE port and looking at the printer output.
Finally, someone mentioned a 359pp, 360ppi, 361ppi test resulting in some aliasing artifacts. Has this test been done at 239,240,241 or 479,480,481 to see if the same occurs?