AltProcessDensitone is a trim tool. It assumes the process was calibrated once — typically with StepWedgeDensitone and a step wedge — and keeps it on target as conditions drift: temperature, developer aging, paper batch, humidity.
1. Print as usual
Make a real print through your current correction curve. No wedge, no test
target: the print you were making anyway is the calibration data. Note which
.acv you used — the whole method depends on knowing it.
2. Scan the dry print
Fixed scanner settings: RAW with a straight curve, no auto-exposure, no auto-levels, no sharpening, the same every time — Scanning a Print for Measurement. Get the whole print in frame, including a little of the paper margin and the coating border if there is one: those are what the app prefers for the white and black anchors.
3. Load the pair and check the registration
Load the source image (the positive the negative was made from) and the scan. Registration is automatic; verify it in Overlay and Diff and drag corners if needed.
Fill in Method and Paper while you are here; they name the exports and go into the ICC profile description.
4. Load the active curve
Load the .acv that was applied when this negative was made. This is what
makes the output a replacement curve: the measured error is composed with
the curve that produced the print.
5. Judge the measurement before you trust it
- Coverage — the status pill and the statistics panel report how much of the tone scale the image exercised. A high-key portrait says nothing about deep shadows, and those tones are left on your current curve rather than invented.
- Endpoints — white and black points carry their provenance. estimated in red means the image had no highlights or no shadows to read.
- Confidence — per-bin in the table, and as grey bands on the graph.
- Preview — the honest gut check: current print on the left, the simulated corrected print on the right.
6. Export and reprint
⌘E writes the replacement .acv. Regenerate the negative through it and
print. Small corrections converge quickly. ⌘S saves the .apdt session
beside the scan so the measurement is reproducible — put the darkroom
context that decided this print (exposure, humidity, coating batch) in the
inspector’s Notes first, and it travels with the session and prints on
both reports.
File → Close Session then hands the window an empty canvas for the next sheet while keeping your curve, Method and Paper, and analysis settings.
7. Repeat with the next print
Each print you make is another data point. Correcting from the print you just made — rather than from a wedge you printed last month — is what keeps a process on target through a season.
When to go back to a wedge
Drift correction keeps a good curve good; it does not establish one. Print a wedge and use StepWedgeDensitone when you:
- change paper stock or manufacturer
- change chemistry formula, dilution, or process entirely
- see a large measured error, or coverage too low to correct with confidence
- have no idea which curve produced the print you are holding