Correction curves

Choosing one

Correction curve sits in the options column, above the divider, because it applies to every file you save rather than to one frame.

SaltPrint ships with several, named for what they do rather than for a process — the same process behaves differently in different hands. Pick one and watch the preview. They're a starting point, not an answer.

Making your own

• Curve Builder Wizard… — the guided job, and the honest answer: print a 21-step target, expose and process it, photograph or scan the result, and it builds a curve from what actually happened. It saves as it goes, so you can stop after the printing and come back days later. Full detail on the curve target page.
• Manual Curve… — shape one by hand, with Shadows, Midtones and Highlights as the handles. Useful when you know what you want changed and don't need to measure it.
• Import curve file… — bring in a curve you already have, including ones exported from other software.

A curve and a coloured scale are two levers, not two answers

They work on the same problem from opposite ends, and you can use either, both, or neither.

• A correction curve changes the tones in the file. It's precise, it costs nothing to try, and it can only work with the range your negative is physically able to produce.
• A coloured tonal scale changes how the negative blocks UV. It can extend that physical range — which is why a colour sometimes rescues a print no curve could — but it's coarse, and what it does depends on your printer and your process.

Use a curve on its own if plain black already gives you the range and you only need to redistribute it. Use a colour on its own if the negative simply isn't dense enough and you don't yet want to measure anything. Use both together — the usual end point — when you've found the colour that gives your process the most to work with, then measured a curve to place the tones inside it.

The order matters. A measured curve describes the whole chain that produced it: your printer, your paper, your chemistry and the scale colour selected when you printed the target. Change the colour afterwards and the curve describes something you're no longer doing. Settle the colour with a test sheet first, then measure the curve — otherwise you'll measure twice.

Managing the ones you've made

Correction Curve ▸ Manage curves… lists your curves and lets you rename or delete one.

• The name is yours. Curves you make are called what you call them, and that name is never translated — switch the app to French and your curve keeps its name. Name them after what they describe: the paper, the process, the date you measured them.
• Deleting sends the file to the Trash or Recycle Bin, not into nothing. A curve costs a printed target, a contact print and a scan, so a mis-click is recoverable — go and fish it out.
• The built-in curves aren't yours to rename or delete. They're always there as a starting point.