Printing, and how SaltPrint knows about your printer

Choosing a printer

The printer dropdown in the print-size block lists the printers your system has installed. SaltPrint asks the OS for that list — macOS and Windows each have their own way of being asked — and starts on your system default printer, the same one your other applications would use.

Choosing a printer here is not the same as printing to it. It's how SaltPrint knows which printer's margins to use when it works out how large the image can be on your paper. Pick the one you'll actually print the negative on, even if you press Print later from somewhere else.

If you select a printer, and later that printer is gone — unplugged, removed, renamed — SaltPrint keeps it in the list rather than quietly switching you to another. Swapping it silently would change the margins, and therefore the size of every print you make, without saying a word. A printer in the list that isn't installed is telling you something.

Where the margin number comes from

No desktop printer prints to the edge of its own paper. Every one keeps an unprintable margin, and it differs by model, by paper size and sometimes by tray.

So SaltPrint asks. On macOS it reads the printable area the print system reports for that printer and sheet; on Windows it asks the printer's driver through the graphics layer for the same thing. Both are the OS's own answer, not a guess and not a lookup table we maintain.

That answer can be confidently wrong. When a printer isn't properly mapped — no driver installed, a generic queue, a network printer the system hasn't fully learned about — the OS falls back to a generic description and returns a plausible-looking margin that has nothing to do with your hardware. It doesn't report an error. Measured here: three different printers returned byte-identical margins from a generic driver, in silence.

Which is why SaltPrint shows you the number, says where it came from, and lets you replace it. If you know your printer's real margin, type it.

Measure it once, with a ruler

The reliable way to settle this takes one sheet of plain paper:

• Set Fit the sheet, choose your paper, and print any image on ordinary paper — not film; this is a measurement, not a negative.
• Measure the white border on all four sides with a ruler.
• Type what you measured into the margin field.

From then on the size SaltPrint reports is the size you'll get. Worth doing once per printer.

If you must guess, guess large. Erring generous costs you a little image size. Erring small clips the edges off your negative, and you find out after the chemistry.

Pressing Print

The Print button sends the current negative to the system print dialog at the size the print-size block reports. From there it's your printer's own dialog — the same one you know — where the paper type, quality and ink settings live.

Those settings are the driver's, not SaltPrint's. This matters more than it sounds: for transparency film you generally want the media type and quality your film maker recommends, and none of that is something SaltPrint sets or can see. Set it in the print dialog as you would for any other application.

You can also skip the button entirely. The saved TIFF is an ordinary file — print it from whatever application you prefer. Just make sure that application doesn't rescale it, or the size SaltPrint calculated stops being the size that lands on the film.

What SaltPrint does not know

Worth being explicit:

• It doesn't know which inks your printer has. It writes a colour value and the driver decides what to lay down to make it. A "yellow" negative is a request, not an ink selection — which is exactly why the test sheets exist instead of advice.
• It doesn't know your printer's true resolution. There's no portable way to ask, so the DPI box takes your word and warns when the file is heading somewhere expensive. See print size.
• It doesn't know whether the print came out right. Nothing does, until you look at the paper.