This is the end-to-end loop for calibrating one process/paper combination. For the scanning setup every step of it depends on, see Scanning a Print for Measurement.
1. Print and scan a step wedge
Print a step wedge (21, 31 or 51 steps are the usual choices) through your digital-negative process, using your standard chemistry, paper and exposure. Let it dry fully — alt-process prints dry down, and a damp print measures darker than it will ever look again.
Scan with fixed settings: RAW with a straight curve, no auto-exposure, no auto-levels, no sharpening — see Scanning a Print for Measurement. Use the same settings for every wedge you ever measure. All readings are normalized to the wedge’s own lightest and darkest patch, so consistency matters far more than absolute accuracy.
2. Load and orient
Drop the scan onto the canvas. Use the toolbar rotate buttons if it came in sideways; the geometry follows the rotation and the file on disk is not touched.
3. Set the layout, detect, then verify
In the inspector’s Measurement section, set Cols, Rows and Steps to the wedge you printed, then click Detect Corners. (Use Detect Corners and Steps instead when you do not know the layout — it predicts all of it and overwrites the pickers.) Then check:
- The outline hugs the printed wedge — drag the corner handles if not.
- The grid matches your wedge — the Cols / Rows / Steps pickers, with canonical layouts one click away.
- The cell order — the toolbar’s axis toggle and corner picker decide which corner is step 0 and which way the numbering runs. Detect Corners and Steps predicts both; correct them here if your wedge runs the other way.
Nudge any circle that landed on a dust speck or a coating defect.
4. Record what you printed
Fill in Method and Paper, and put the details you will want in six months into Notes — exposure time, humidity, coating batch, developer dilution. All three are saved with the session and printed on the reports; the notes field is what turns a folder of scans into a usable record.
5. Smooth the readings
Pick a smoothing mode and window in the Processing section — enough to tame scanner noise, not so much that real tonal structure disappears. Watch the Normalized series on the graph and the Δ column in the table as you change it.
6. Compose with the active curve
If the negative was printed through an existing .acv, load it in the
Curve section. This is what makes the export a replacement curve
rather than a correction to stack on top.
7. Export
- Export → Save Adjusted Curve… — the corrected
.acvfor Photoshop - Export → Generate PDF Report… — the sheet for the darkroom notebook
- Export → Generate CSV Report… — the numbers for a spreadsheet
- Export → Export ICC Profiles… — for soft-proofing the next image before you print it
8. Save the session
⌘S writes a .wdge beside the scan. The session is autosaved anyway, but
a named file is what lets you come back to this exact measurement — and
re-export from it — months later.
9. Verify with a second print
Make the wedge again through the new curve and measure it the same way. The steps should now land evenly across the tonal range: σ (residual) drops, the Δ column goes green, and the shaded band between Raw and Target on the graph collapses toward nothing.
Then stop printing wedges
Once the base curve is dialled in, day-to-day drift — temperature, developer aging, paper batch, humidity — can be corrected from ordinary prints with AltProcessDensitone instead of printing a fresh wedge each time. Come back to a wedge when you change paper stock, chemistry or process.